English Assignment 2

World Psychiatry 19:2 - June 2020 179

FORUM – ASSESSING THE PUBLIC HEALTH EFFECTS OF THE LEGALIZATION OF RECREATIONAL CANNABIS USE

Assessing the public health impacts of legalizing recreational cannabis use: the US experience

Wayne Hall1,2, Michael Lynskey2

1University of Queensland Centre for Youth Substance Abuse Research, Brisbane, Australia; 2National Addiction Centre, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK

The sale of cannabis for adult recreational use has been made legal in nine US states since 2012, and nationally in Uruguay in 2013 and Canada in 2018. We review US research on the effects of legalization on cannabis use among adults and adolescents and on cannabis-related harms; the impact of legalizing adult recreational use on cannabis price, availability, potency and use; and regulatory policies that may increase or limit adverse effects of legalization. The legalization of recreational cannabis use in the US has substantially reduced the price of cannabis, increased its potency, and made cannabis more available to adult users. It appears to have increased the frequency of cannabis use among adults, but not so far among youth. It has also increased emergency department attendances and hospitalizations for some cannabis-related harms. The relatively modest effects on cannabis use to date probably reflect restrictions on the number and locations of retail cannabis outlets and the constraints on commercialization under a continued federal prohibition of cannabis. Future evaluations of legalization should monitor: cannabis sales vol- umes, prices and content of tetrahydrocannabinol; prevalence and frequency of cannabis use among adolescents and adults in household and high school surveys; car crash fatalities and injuries involving drivers who are cannabis-impaired; emergency department presentations related to cannabis; the demand for treatment of cannabis use disorders; and the prevalence of regular cannabis use among vulnerable young people in mental health services, schools and the criminal justice system. Governments that propose to legalize and regulate cannabis use need to fund research to monitor the impacts of these policy changes on public health, and take advantage of this research to develop ways of regulating can- nabis use that minimize adverse effects on public health.

Key words: Cannabis, legalization, recreational use, public health impacts, cannabis potency, cannabis-related harms, emergency department attendances, vulnerable young people

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Cannabis is globally the most widely used illicit drug under international con- trol. In 2017 it was estimated to be used by 188 million adults (range 164-219 million) worldwide or 3.8% of the global adult population1. Cannabis use is more com- mon in North America and high-income countries in Europe and Oceania2. Its use has increased in some low- and middle- income countries, but remains low in Asia1.

The inclusion of cannabis in the same schedules of the international drug con- trol treaties as heroin, cocaine and am- phetamines has been controversial, and public campaigns to legalize its use have been ongoing since the late 1960s3. The route to legalization of adult use in the US began with citizen-initiated referenda that legalized the medical use of cannabis, initially for serious illnesses like cancer, but progressively under liberal regulations that allowed the supply of cannabis by re- tail commercial cannabis “dispensaries”. These changes helped to reduce public opposition to the legalization of adult can- nabis use, which was first achieved by the passage of referenda in two states with

some of the most liberal medical cannabis laws, Colorado and Washington State, in 20124.

Combinations of arguments attracted public support for recreational cannabis legalization in the US, as indicated by cit- izen-initiated referenda5. The first is that cannabis use is common among young adults and causes less harm than alcohol, tobacco and opioids6,7. The second is that making cannabis use a criminal offence causes more harm than cannabis use it- self, because some users are arrested and receive criminal records. The third is that these criminal laws disproportionately affect cannabis users in minority popula- tions, such as African Americans and Lati- nos. The fourth is that legalization of adult use is a better social policy than criminali- zation because: a) it eliminates the illicit market; b) it enables cannabis use to be regulated to minimize adolescent access and protect adult cannabis consumers – e.g., by controlling the tetrahydrocan- nabinol (THC) content of cannabis prod- ucts and reducing levels of contaminants – such as fungi, heavy metals and pesti- cides – found in illicitly produced canna-

bis; c) it reduces the costs of policing the prohibition of cannabis use (freeing police resources to address more serious crimes); and d) it enables governments to raise rev- enue by taxing the sale of cannabis prod- ucts5.

In principle, adult cannabis use could be legalized in a range of different ways8. Individuals could be allowed to grow can- nabis for their own use and gift it to others. They could be allowed to form cannabis growers’ clubs that produce cannabis solely for their members’ use. The govern- ment could create a monopoly in cannabis production and sales in order to minimize the promotion of cannabis use, as some US states and Canadian provinces have done with alcohol. The government could license non-profit cooperatives or chari- table cooperatives that produce and sell cannabis without making a profit. Finally, governments could allow the commer- cialization of cannabis production and sale under a for-profit model like that used for alcohol8.

Since 2012, eleven US states and the nation states Canada and Uruguay have passed legislation that has made it legal

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for adults to produce, process and use can- nabis. Nine US states, Uruguay and Cana- da now permit legal retail cannabis sales as well. In Washington DC and Vermont, it is legal for adults to grow cannabis for their personal use and to give it to friends, but it remains illegal to sell it8-10.

The creation of a legal cannabis market is more radical than the policy changes during the 1970s, which removed criminal penalties or imprisonment for personal use and possession, but left the supply of cannabis to the illicit market. Legalization permits the establishment of a legal canna- bis industry that has an interest in promot- ing cannabis use and, unlike policies that legalize medical cannabis use, it allows adults to use cannabis for any purpose.

Most US states that have legalized retail cannabis sales have followed Colorado and Washington State1 in using the same regulatory approach as for alcohol, i.e. li- censing companies to produce and sell cannabis for a profit11,12. States differ in whether they separately license growers, processers, suppliers and retail sellers or whether they allow licensees to perform all of these roles (“vertical integration”)13,14.

All states have set the same minimum legal purchase age for cannabis as for al- cohol, i.e. 21 years. Many have limited the quantity of cannabis that an adult can legal- ly carry to 28.5 g15,16. In most states, canna- bis products are taxed on their sale price17, but tax rates vary between states1. Drug- impaired driving is an offence in all states that have legalized cannabis (and in many US states that have not), but states differ in how they have enforced this law13.

In 2013, Uruguay became the first na- tion to legalize adult cannabis use. It did so by allowing adults to use cannabis if they registered with the state and used one of three ways to obtain cannabis18: they could grow their own cannabis, join a cannabis growers’ club that would pro- duce enough cannabis for its members, or purchase cannabis (produced under gov- ernment licence) from pharmacies19,20. The policy was introduced in phases. In the first, registered cannabis users were allowed to grow their own cannabis. In the second, cannabis growers’ clubs were licensed. In the third, a small number of pharmacies were licensed to supply can-

nabis to registered users1. The Uruguayan model is still in the early

stage of implementation. So, it is difficult to assess whether it has achieved its goals. Some have argued that the model is too re- strictive to undermine the illicit cannabis market20,21. So far only 6,965 persons have registered to grow their own cannabis and there are 115 cannabis clubs with 3,406 reg- istered members. Only 16 pharmacies (from a total of 1,200) supply cannabis, and 34,696 persons1 have registered to purchase can- nabis from pharmacies22. The total of 45,067 registered cannabis users comprise just under half the estimated number of can- nabis users in Uruguay. We do not yet know what proportion of registered and unregis- tered cannabis users still purchase cannabis from the illicit market.

In October 2018, Canada became the second nation to legalize the sale of canna- bis to adults23,24. The goals of legalization were to eliminate the illicit cannabis mar- ket and regulate the production and sale of cannabis to protect public health and minimize youth uptake25. The federal gov- ernment licenses and regulates cannabis producers; advertising of cannabis is not permitted; and cannabis products must be sold in plain packaging with health warn- ings. The minimum legal purchase age is 18 (unless a provincial government sets a higher one), and it is an offence to drive while impaired by cannabis.

Provincial governments in Canada reg- ulate wholesale and retail cannabis sales in the same way as they regulate alcohol26. Provinces with an alcohol retail monopo- ly can use the same regulatory approach for cannabis, and retail cannabis sales are allowed in provinces that licence for-prof- it retailers of alcohol. The Canadian feder- al government collects taxes on cannabis and shares these revenues with provincial governments. The sale of edible cannabis products and cannabis extracts began in October 2019, with taxes based on their THC content.

As is the case with Uruguay, Canadian policy is still at an early stage of imple- mentation. So, it is too early to evaluate its impact. The remainder of this paper ac- cordingly focuses on the impacts to date of the legalization of recreational cannabis use in the US.

HOW HAS RECREATIONAL LEGALIZATION AFFECTED CANNABIS MARKETS IN THE US?

The legalization of recreational can- nabis use in the US has had a number of effects. First, it has been followed by a sub- stantial decrease of the retail price of can- nabis17. Second, it has allowed adults to obtain a regular supply of cannabis with- out risk of criminal penalty. Third, it has produced a major diversification of the cannabis products for sale27. In addition to cannabis flower, cannabis retail outlets also sell high-potency cannabis extracts (wax, shatter), edible cannabis (e.g., gum- my bears, candy and chocolates), and can- nabis infused beverages17. These products presumably meet the needs of a broader range of adult consumers than the illicit market primarily catered to, namely, daily or near daily cannabis smokers17. The in- creased availability and marketing of can- nabis, and more publicly visible canna - bis use by adults, may make cannabis use more socially acceptable and enable more adults to use cannabis for a longer period of their lives than has been the case under prohibition.

Cannabis prices have fallen steeply in the US states that have legalized its recre- ational use17,28,29. Prices no longer need to include a premium to compensate illicit producers and sellers for the risks of being arrested or imprisoned or subjected to vi- olence by other illicit market participants. Legal cannabis production is no longer small scale and clandestine, allowing growers to increase the scale of produc- tion, reduce their costs, and pass these on to consumers in the form of lower prices. If states allow licensees to grow, process and sell cannabis wholesale and retail, as in Colorado, then cannabis production can become even more efficient29.

Most US legalization states have im- posed taxes on the retail price of cannabis products29. This method of taxing canna- bis has had two consequences: state can- nabis tax revenue has declined as retail prices have fallen; and cannabis produc- ers and retailers have had an incentive to increase the THC content per gram of product to reduce prices and increase profits29. Taxes may have contributed to

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the increased sale of cannabis extracts with a THC content of 70% or more (21% of all sales in some states). The increase in cannabis potency presumably satisfies the preferences of daily cannabis users (who account for most sales). A cap on THC content or a minimum unit price or tax based on THC content would reduce this incentive8, but so far no US state has adopted any of these policies.

Cannabis prices may decline further. Lo cal regulations have restricted up to now the number and location of retail outlets in some states to the larger cities30. Cannabis prices are likely to fall much further if legal- ization of adult use becomes US national policy, because this would allow cannabis production on a larger scale, potentially per- mit the establishment of inter-state com- merce, facilitate the increase in multi-state operations, allow the development of US- based multinational companies via merg- ers and acquisitions, and attract large scale investment from the alcohol, tobacco and finance industries.

Historical experiences with the regula- tion of alcohol and tobacco31,32 suggest that, in the short term, increasing access to more potent cannabis products at a lower price is likely to increase the frequency of cannabis use among current users. In the longer term, a profit-seeking legal canna- bis industry is likely to attempt to increase the number of cannabis users, and the reg- ularity of their use, in order to maximize its profits. This will involve a combination of promotional activities (e.g., media adver- tising, price discounts, and discounts for regular purchasers) that aim to increase the number of daily cannabis users and the proportion of adults who use cannabis. There is considerable uncertainty about how much and how soon such promotion- al activities will succeed. Experience with alcohol suggests, however, that the larger the proportion of the population that uses cannabis, and the more often they do so, the larger will be any adverse public health impacts of cannabis legalization31.

In the remainder of this paper, we re- view evidence on the public health effects to date of the legalization of recreational cannabis use in the US. As an early adop- ter, the US is likely to influence the policies adopted in other countries that decide to

legalize cannabis use. Moreover, the US collects survey data on patterns of canna- bis use in the population and health data on cannabis- and alcohol-related harms. As Canada and Uruguay proceed to im- plement cannabis legalization, similar high quality survey33,34 and other data will be collected to assess the public health impacts of legalization in these countries.

WHAT ADVERSE HEALTH EFFECTS MAY INCREASE AFTER CANNABIS LEGALIZATION?

We summarize here the adverse effects that may increase if harmful patterns of cannabis use, especially daily use, increase as a result of legalization. The content is based on reviews of the evidence on the adverse health effects of cannabis35-37 and analyses of health outcomes that should be monitored after cannabis legalization 38-40.

Acute effects

Car accidents may increase if more can- nabis users drive, or drive more often, while impaired, or if cannabis users who drive use more potent cannabis products36,37. More cannabis users may present to emer- gency departments with acute psychologi- cal distress and psychotic symptoms if they use more potent cannabis products such as extracts36. Adverse effects of cannabis on fetal development36,37 may increase if more women use cannabis during pregnancy, as appears to be the case in the US41.

Relationships between cannabis use and the use of alcohol, tobacco and opioids will substantially affect the public health impacts of cannabis legalization38,40,42. The public health burdens of these drugs could be reduced if cannabis becomes a substi- tute, while their impact could be amplified if there is more concurrent use of cannabis and these drugs38,40.

Chronic effects

More frequent use of potent cannabis may increase the prevalence of cannabis

dependence, i.e. more cannabis users will experience impaired control over their cannabis use despite such use harming them43. The 9% risk of dependence among lifetime users in the US in the early 1990s may increase in those who use more po- tent cannabis products44.

Daily cannabis users have impaired co- gnitive performance that appears to be re- versed by abstinence45. Adolescents and young adults who are regularly intoxicat- ed during their schooling have poorer ed- ucational attainment46. Cannabis-related cognitive impairment may also occur in older adults who regularly use cannabis for recreational purposes47.

Daily cannabis use is associated with an increased risk of psychotic symptoms or a diagnosis of a schizophreniform psycho- sis in prospective epidemiological stud- ies48,49. These risks are higher in those who begin cannabis use in adolescence, those who use it more often and for longer48, and those who use strains with high THC and/ or low cannabidiol50. Psychotic symptoms occur two years earlier on average in regu- lar cannabis users51, and persons with a psychosis who continue to use cannabis have more frequent episodes and longer periods of hospitalization for their illness- es52. In major European cities, an associa- tion has been reported between average cannabis potency and the incidence of psychosis53.

Heavy cannabis users can develop a hyperemesis syndrome54, with severe ab- dominal pain and cyclical vomiting. The syndrome is most often reported by daily cannabis users in the absence of any other medical cause55. It is relieved by hot bath- ing56, resolves when users abstain from using cannabis, and may recur if they re- start cannabis54. A small number of deaths have been attributed to complications of this syndrome57.

Case series and a case-control study58 suggest that heavy cannabis smoking may increase cardiovascular disease risk in young heavy cannabis smokers59-61. Mid- dle-aged men who have had a myocardial infarction may experience angina if they smoke cannabis62, and are at increased risk of a recurrence if they are cannabis users63-65.

Cannabis-only smokers report more

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cough, sputum and wheezing than per- sons who do not smoke cannabis66-71, and these symptoms remit if they quit72. How- ever, cannabis smokers do not appear to be at higher risk of chronic obstructive pul- monary disease72,73.

Systematic reviews have not found an association between cannabis use and head or neck cancer74, or lung cancer75. By contrast, a meta-analysis of three studies76 found a small increase in risk of testicular cancer among high-frequency cannabis users and in those who had used cannabis for ten or more years.

HEALTH EFFECTS OF LEGALIZING RECREATIONAL CANNABIS USE IN THE US

State level legalization of recreational cannabis use for adults was only imple- mented about five years ago in Washington State and Colorado, the US jurisdictions with the longest experience of a legal re- gime to date. This is probably too short a period to judge the full effects of legaliza- tion. It has taken time to produce depend- able supplies of cannabis within states that have legalized, and there are a limited number of retail outlets available in a rela- tively small number of locations in these states1. For these reasons, evaluations of the first five or so years after legalization may provide a poor indication of the im- pacts of cannabis use on public health when the industry develops over a decade or more42,77.

Effects on cannabis use

If experience with alcohol and tobacco is a reasonable guide, we would expect de- clines in cannabis prices to be followed by increases in the frequency of use among existing users31,32,78. There is some evi- dence of increased frequency of use in re- sponse to the relatively small declines in cannabis prices that occurred under pro- hibition79. It is more difficult to estimate how much cannabis use may increase when cannabis prices fall by 30-50%80.

Household survey data suggest that lower cannabis prices have increased the

frequency of use among adult cannabis users in US states that have legalized rec- reational cannabis78,81,82. Surveys in Colo- rado and Washington State have found mixed evidence on the impacts of can- nabis legalization on adolescent cannabis use. There was an increase in cannabis use among students after legalization in Washington State, but a decrease among adolescents in Colorado83,84. No changes in cannabis use were reported among youth in two surveys in Washington State conducted the year before and the year after legalization of recreational use was implemented84. Darnell and Bitney85 did not find changes in youth cannabis use in Washington State between 2002 and 2016. Anderson et al86 failed to find an increase in youth cannabis use in the Youth Risk Behavior Surveys in the four years before and the three years after the legalization of recreational use. Dilley et al87 reported very similar results in analyses of Youth Risk Behaviour Surveys in Washington State.

Cerdá et al81 recently compared trends in regular past 30 day cannabis use and cannabis use disorders among adoles- cents and young adults in US states that have and have not legalized recreational cannabis use, using data from the US drug household survey, the National Survey on Drug Use and Health. They found sugges- tive evidence of a small increase in these outcomes among 12-17 year olds, but did not find any similar effects among those aged 18-25 years. They were cautious in interpreting the former, because they es- timated that the small increases could be due to unmeasured confounders. This was a less plausible explanation for simi- lar increases observed in regular cannabis use and cannabis use disorders among adults 26 years and older81.

Effects on cannabis-related hospitalizations

Cannabis-related hospitalizations have increased in Colorado after recreational cannabis use was legalized. These increas- es have been in addition to earlier increases that occurred after the legalization of medi- cal cannabis use88. After cannabis legali-

zation in Colorado there have also been increases in hospitalizations for cannabis abuse and dependence89, motor vehicle accidents and injuries related to cannabis abuse90, and head injuries attributed to an increase in falls91.

An increase in emergency department presentations for hyperemesis in Aurora, Colorado was reported after medical can- nabis use was legalized in 2000, and a fur- ther increase after recreational use legali- zation92. A 46% increase in the incidence of cyclic vomiting was reported between 2010 and 2014 in the Colorado State Inpa- tient Database93.

An increase in cannabis-related emer- gency department presentations has been reported after legalization in Boul- der, Colorado for childhood poisonings, psychological distress in adults, severe vomiting, and severe burns in users who had attempted to extract THC from can- nabis oils using butane94.

Calcaterra et al95 analyzed trends in can- nabis- and alcohol-related presentations to a hospital network in Colorado that provid- ed emergency medical care to low-income patients in two periods: January 2009 to December 2013 and January 2014 to De- cember 2015. The rate of cannabis-related presentations increased steeply in the lat- ter period, while presentations involving alcohol were unchanged. Cannabis-related presentations were more likely to involve younger adults and more likely to lead to hospitalization, especially for psychiatric care.

In Colorado, emergency department pres- entations for mental illness with a canna- bis-related code increased five times faster than mental illness presentations without such a code between 2012 and 201488. The largest increases were for persons who re- ceived diagnoses of schizophrenia and oth er psychotic disorders, suicide and intentional self-harm, and mood disorders96.

A review of pediatric cases from 1975 to 2015 found more unintentional canna- bis ingestion by children in US states that had legalized medical and recreational cannabis use97. This increase prompted limits on package and serving sizes of ed- ible cannabis products in 201798. Despite these changes, pediatric hospital visits and calls to poison centres for cannabis

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ingestion increased after 2017. Similar increases in accidental poisoning among children and adolescents were reported in Massachusetts before and after the legalization of medical cannabis use, de- spite the use of child-proof packaging and warning labels99.

Effects on road crashes

Studies of the effects of cannabis legali- zation on traffic accidents have produced mixed findings.

Chung et al100 reported an increase in the rate of patients admitted to Colorado hospitals for traumatic injury who were cannabis-positive between 2012 and 2015, in the absence of any corresponding in- crease in neighbouring states that had not legalized cannabis.

However, Aydelotte et al101 did not find greater changes in traffic fatality rates in Washington State and Colorado using Fa- tality Analysis Reporting System (FARS) data than in neighbouring states that had not legalized cannabis. Sevigny102 ana- lyzed FARS data (1993-2014) using data imputation to address the large amount of missing data, and did not find an impact of legalization on cannabis-positive driv- ing among people involved in a fatal crash. Lane and Hall103 found a short-term in- crease in traffic fatalities in both US states that had legalized the commercial sale of cannabis (i.e., Colorado, Washington State and Oregon) and their neighbouring juris- dictions.

Treatment seeking for cannabis use disorders

Darnell and Bitney85 compared trends in treatment seeking for cannabis use dis- orders in the Treatment Episode Data Set in Washington State in the first two years after legalization with trends in a synthet- ic cohort comprising a weighted sample of other US states that had not legalized cannabis. Treatment demand declined in Washington State after legalization, but at the same rate as it declined in states that had not legalized cannabis.

MONITORING THE FUTURE PUBLIC HEALTH IMPACT OF CANNABIS LEGALIZATION

There are a number of reasons why the effects of cannabis legalization to date may underestimate its full impacts on public health in the longer term.

First, the commercialization of the can- nabis industry is incomplete in the US. While cannabis remains prohibited under US federal law, there are also prohibitions on inter-state commerce in cannabis and investment by the alcohol, tobacco and finance industries. It is difficult for canna- bis businesses to use banks or to advertise cannabis, because it remains an illegal commodity. National cannabis legaliza- tion would remove these constraints and allow the full commercialization of the cannabis industry under constitutional protections including the “commercial freedom of speech”.

Second, it is too soon to evaluate the ef- fects of cannabis legalization in Canada and Uruguay. Both countries are still imple- menting their models, so it will take time for legalization to become fully operation- al.

Third, even after legalization is fully im- plemented, one would expect a delay be- tween any increases in cannabis use and the detection of increased problems re- lated to regular cannabis use in the health care system. The following section discuss- es indicators that should be monitored to evaluate the longer-term public health im- pacts of cannabis legalization.

Potential indicators of future cannabis-related harm

Studies of the public health impacts of legalization should monitor trends in acute harms that are likely to increase if more adults use more potent cannabis prod- ucts more often. These include: car crash fatalities and injuries involving cannabis- impaired drivers; emergency department attendances for myocardial infarctions, acute coronary syndromes and strokes in young adults58,104-106, and cyclic vomiting in young adults.

Treatment seeking for cannabis depen- dence should also be monitored. It is un- certain how legalization may affect it. One would expect a decline in treatment seek- ing among adult cannabis users who will no longer be legally coerced into treat- ment as an alternative to imprisonment. Adolescents with cannabis use problems may still be arrested107 and coerced into treatment, and their numbers may in- crease if courts use treatment as an alter- native to their criminal prosecution if they are caught using cannabis.

Legalization may also reduce treatment seeking among persons with cannabis prob- lems if increased access to legal and cheap cannabis products reduces the economic costs of cannabis use and social pressure from families and friends to stop using can- nabis. On the other hand, legalization of adult use may reduce the stigma attached to problem cannabis use and thereby en- courage earlier treatment seeking, e.g. if education campaigns increase public rec- ognition of cannabis use disorders and en- courage users to seek treatment.

The US national treatment data108 will provide useful information on these trends. These data could be expanded to include information from new treatment entrants on: reasons for seeking treatment; the type and amounts of cannabis used; usual routes of administration; and where they obtained their cannabis (to assess how many prob- lem users are still using the illicit market).

A major research priority should be to improve assessments of the role that can- nabis-impaired driving plays in fatal motor vehicle accidents. This research should as- sess the degree to which cannabis is a sub- stitute for alcohol among young men, and the extent to which it reduces other types of alcohol-related harm, such as suicides and assaults.

It will be important to monitor any ef- fects that cannabis legalization has on to- bacco smoking and alcohol use among adolescents and young adults. With the decline in youth tobacco use, suggestive evidence has emerged of a “reverse gate- way effect”, in which initiation of cannabis smoking has increased tobacco smoking among young adults109.

The social distributional effects of can-

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nabis legalization should also be examin- ed. One major motivation for cannabis le- galization has been to eliminate the un- equal enforcement of criminal penalties against minority cannabis users. Legaliza- tion has reduced arrests, but it is too early to assess its impact on rates of incarcera- tion and minority differentials in imprison- ment. It will also be important to see if mi- norities are over-represented among prob- lem cannabis users who seek treatment110.

Research should also monitor any ad- verse health effects that cannabis legali- zation has on cannabis users over the age of 50. US surveys report an increase in use among this age group since legaliza- tion111,112, probably for a combination of medical and quasi-medical reasons (e.g., to assist with sleep, control pain, stimulate appetite). Older users may be at higher risk of some adverse health effects, such as car crashes, cardiovascular disease and cognitive impairment.

We need more rigorous evaluations of the public health impacts of cannabis le- galization42. Comparisons of differences between states in time series data on vari- ous causes of hospitalization and death are of limited value because they are not able to test alternative explanations of state level differences77. We also need large prospective studies of the effects of these policy changes on the use of canna- bis and other drugs and their impact on health outcomes in individuals42.

CONCLUSIONS

The legalization of recreational canna- bis use in Canada, Uruguay and an increa- sing number of states in the US is a large scale policy experiment whose effects may not be known for a decade or more. So far legalization has not produced large in- creases in cannabis use among youth in the US. As expected, it has increased regular cannabis use among adult users. It has also increased acute cannabis-related presenta- tions to emergency departments in adults and children for physical and mental health problems related to cannabis use (e.g., psy- chological distress, vomiting syndromes, and accidental poisonings in children). Studies of the effects of the legalization on

motor vehicle crashes are inconsistent. There are limited data on the impacts on treatment seeking for cannabis use dis- orders.

It would be unwise to assume that the modest effects of cannabis legalization observed to date will predict its longer- term effects. The legalization of cannabis markets has already substantially reduced the price of cannabis and increased its potency, and prices are likely to fall fur- ther if legalization becomes national pol- icy in the US. Legalization on the limited scale to date has increased regular can- nabis use among adults and it may have increased cannabis use disorders among adult users, although the evidence on this issue is insufficient. In the longer term, experience with alcohol suggests that more liberal regulation that provides legal access to cheaper, more potent canna- bis products will increase the number of regular users and probably the number of new cannabis users. There is considerable uncertainty about by how many and how soon this may occur.

Future evaluations of the public health impacts of cannabis legalization should assess its effects on: attitudes towards can- nabis use in young people; the frequency of cannabis use in high-risk youth and young adults (e.g., those who seek help for mental health problems and those in the criminal justice system); cannabis-related car crashes and emergency department attendances for cannabis-related prob- lems; treatment seeking for cannabis use disorders and its outcomes; and persons seeking treatment for mental disorders.

Research should also assess how legal- ization affects the use and harms of alco- hol and tobacco and other drug use (e.g., opioids) among youth and young and older adults. In the longer term we need to assess the effects of legalization on the duration of cannabis use in adulthood, because it is likely that legalization will ex- tend the duration of cannabis use beyond the late 20s, the age at which most users desisted under prohibition113. There is some suggestive evidence that the dura- tion of cannabis use has already increased among recent birth cohorts114.

These evaluations should inform the design of policies to reduce cannabis-re-

lated harm after legalization. These may include: tighter regulation of youth ac- cess to cannabis; using taxes to discour- age heavy cannabis use (e.g., by setting minimum prices for cannabis products, imposing potency caps, and basing can- nabis taxes on THC content115); consum- er-tested health warnings about the risks of cannabis use, especially daily cannabis use, such as cognitive impairment and can- nabis dependence; and research to de- velop more effective ways of discouraging adolescents from starting cannabis use116.

ACKNOWLEDGEMENTS

The authors would like to thank S. Yeates for her assis- tance in searching the popular and scientific literature and in preparing this paper for publication.

REFERENCES

1. United Nations Office on Drugs and Crime. World drug report 2019. Vienna: United Nations, 2019.

2. Peacock A, Leung J, Larney S et al. Global sta- tistics on alcohol, tobacco and illicit drug use: 2017 status report. Addiction 2018;113:1905-26.

3. Room R, Fischer B, Hall WD et al. Cannabis pol- icy: moving beyond stalemate. Oxford: Oxford University Press, 2010.

4. Kilmer B, MacCoun RJ. How medical marijuana smoothed the transition to marijuana legaliza- tion in the United States. Annu Rev Law Soc Sci 2017;13:181-202.

5. Felson J, Adamczyk A, Thomas C. How and why have attitudes about cannabis legalization changed so much? Soc Sci Res 2019;78:12-27.

6. Degenhardt L, Whiteford HA, Ferrari AJ et al. Global burden of disease attributable to illicit drug use and dependence: findings from the Global Burden of Disease Study 2010. Lancet 2013;382:1564-74.

7. Global Burden of Disease 2016 Risk Factors Col laborators. Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabol- ic risks or clusters of risks, 1990-2016: a system- atic analysis for the Global Burden of Disease Study 2016. Lancet 2017;390:1345-422.

8. Caulkins J, Kilmer B, Kleiman M et al. Consider- ing marijuana legalization: insights for Vermont and other jurisdictions. Santa Monica: RAND Corporation, 2015.

9. Garvey T, Yeh BT. State legalization of recrea- tional marijuana: selected legal issues. Wash- ington: Congressional Research Office, 2014.

10. US Government Accountability Office. State marijuana legalization, DOJ should document its approach to monitoring the effects of legali- zation. Washington: US Government Account- ability Office, 2015.

11. Hall WD. Alcohol and cannabis: comparing their adverse health effects and regulatory re- gimes. Int J Drug Policy 2017;42:57-62.

12. Room R. Legalizing a market for cannabis for

World Psychiatry 19:2 - June 2020 185

pleasure: Colorado, Washington, Uruguay and beyond. Addiction 2014;109:345-51.

13. Pardo B. Cannabis policy reforms in the Amer- icas: a comparative analysis of Colorado, Wash- ington, and Uruguay. Int J Drug Policy 2014;25: 727-35.

14. Wallach PA, Hudak J. Legal marijuana: com- paring Washington and Colorado. Washington: Brookings Institution, 2014.

15. Quinn S. Alaska allows recreational marijuana as legalization campaign spreads. Reuters, Feb- ruary 24, 2015.

16. Wallach PA. Washington’s marijuana legaliza- tion grows knowledge, not just pot. Washing- ton: Brookings Institution and the Washington Office on Latin America, 2014.

17. Smart R, Caulkins JP, Kilmer B et al. Variation in cannabis potency and prices in a newly legal market: evidence from 30 million cannabis sales in Washington state. Addiction 2017;112:2167- 77.

18. Hudak J, Ramsey G, Walsh J. Uruguay’s canna- bis law: pioneering a new paradigm. Washing- ton: Center for Effective Public Management at Brookings, 2018.

19. Cerdá M, Kilmer B. Uruguay’s middle-ground approach to cannabis legalization. Int J Drug Policy 2017;42:118-20.

20. Walsh J, Ramsey G. Cannabis regulation in Uruguay: an innovative law facing major chal- lenges. J Drug Policy Anal 2016;11.

21. Ramsey G. Getting regulation right: assessing Uruguay’s historic cannabis initiative. Wash- ington: WOLA Advocacy for Human Rights in the Americas, 2016.

22. Instituto de Regulacion y Control de Cannabis. Mercado regulado de cannabis informe VII al 30/06/19. Montevideo: Instituto de Regulacion y Control de Cannabis, 2019.

23. Cox C. The Canadian Cannabis Act legalizes and regulates recreational cannabis use in 2018. Health Policy 2018;122:205-9.

24. Government of Canada. Cannabis Act (S.C. 2018, c. 16). Ottawa: Department of Justice, 2018.

25. Government of Canada. Cannabis legalization and regulation: cannabis is now legal. Ottawa: Department of Justice, 2018.

26. Watson TM, Hyshka E, Bonato S et al. Early-stage cannabis regulatory policy planning across Can- ada’s four largest provinces: a descriptive over- view. Subst Use Misuse 2019;54:1691-704.

27. Spindle TR, Bonn-Miller MO, Vandrey R. Chang- ing landscape of cannabis: novel products, for- mulations, and methods of administration. Curr Opin Psychol 2019;30:98-102.

28. Swanson A, Gamio L. How the price of pot dif- fers in 50 states and 8 major cities. Washington Post, June 22, 2015.

29. Caulkins JP, Hawken A, Kilmer B et al. Marijua- na legalization: what everyone needs to know. New York: Oxford University Press, 2012.

30. Subritzky T, Pettigrew S, Lenton S. Issues in the implementation and evolution of the commer- cial recreational cannabis market in Colorado. Int J Drug Policy 2016;27:1-12.

31. Babor T, Caetano R, Casswell S et al. Alcohol: no ordinary commodity: research and public policy, 2nd ed. Oxford: Oxford University Press, 2010.

32. Chaloupka FJ, Warner KE. The economics of smoking. In: Newhouse JP, Cuyler AJ (eds). The handbook of health economics. New York: El- sevier, 2000:1539-627.

33. Statistics Canada. Analysis of trends in the prev-

alence of cannabis use and related metrics in Canada. Ottawa: Government of Canada, 2019.

34. Statistics Canada. National cannabis survey, first quarter 2019. Ottawa: Government of Can- ada, 2019.

35. Babor T, Caulkins JP, Fischer B et al. Drug policy and the public good, 2nd ed. New York: Oxford University Press, 2018.

36. Hall WD, Renström M, Poznyak V. The health and social effects of nonmedical cannabis use. Geneva: World Health Organization, 2016.

37. National Academies of Sciences Engineering and Medicine. The health effects of cannabis and cannabinoids: the current state of evidence and recommendations for research. Washing- ton: National Academies Press for the National Academies of Sciences Engineering and Medi- cine, 2017.

38. Fischer B, Russell C, Rehm J et al. Assessing the public health impact of cannabis legalization in Canada: core outcome indicators towards an ‘index’ for monitoring and evaluation. J Public Health 2019;41:412-21.

39. Hall WD, Lynskey M. Evaluating the public health impacts of legalizing recreational canna- bis use in the United States. Addiction 2016;111: 1764-73.

40. Windle SB, Wade K, Filion KB et al. Potential harms from legalization of recreational cannabis use in Canada. Can J Public Health 2019;110:222- 6.

41. Volkow ND, Han B, Compton WM et al. Self-re- ported medical and nonmedical cannabis use among pregnant women in the United States. JAMA 2019;322:167-9.

42. Choo EK, Emery SL. Clearing the haze: the com- plexities and challenges of research on state mari juana laws. Ann NY Acad Sci 2017;1394:55- 73.

43. Budney AJ, Sofis MJ, Borodovsky JT. An update on cannabis use disorder with comment on the impact of policy related to therapeutic and recreational cannabis use. Eur Arch Psychiatry Clin Neurosci 2019;269:73-86.

44. Freeman TP, Winstock AR. Examining the pro- file of high-potency cannabis and its association with severity of cannabis dependence. Psychol Med 2015;45:3181-9.

45. Scott JC, Slomiak ST, Jones JD et al. Association of cannabis with cognitive functioning in ado- lescents and young adults: a systematic review and meta-analysis. JAMA Psychiatry 2018;75: 585-95.

46. Horwood L, Fergusson D, Hayatbakhsh M et al. Cannabis use and educational achievement: findings from three Australasian cohort studies. Drug Alcohol Depend 2010;110:247-53.

47. Auer R, Vittinghoff E, Yaffe K et al. Association between lifetime marijuana use and cognitive function in middle age: the Coronary Artery Risk Development in Young Adults (CARDIA) Study. JAMA Intern Med 2016;176:352-61.

48. Marconi A, Di Forti M, Lewis CM et al. Meta- analysis of the association between the level of cannabis use and risk of psychosis. Schizophr Bull 2016;42:1262-9.

49. Gage SH, Hickman M, Zammit S. Association between cannabis and psychosis: epidemio- logic evidence. Biol Psychiatry 2016;79:549-56.

50. Di Forti M, Marconi A, Carra E et al. Proportion of patients in south London with first-episode psychosis attributable to use of high potency cannabis: a case-control study. Lancet Psychia-

try 2015;2:233-8. 51. Large M, Sharma S, Compton MT et al. Canna-

bis use and earlier onset of psychosis: a system- atic meta-analysis. Arch Gen Psychiatry 2011; 68:555-61.

52. Schoeler T, Monk A, Sami MB et al. Continued versus discontinued cannabis use in patients with psychosis: a systematic review and meta- analysis. Lancet Psychiatry 2016;3:215-25.

53. Di Forti M, Quattrone D, Freeman TP et al. The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study. Lancet Psychiatry 2019;6:427-36.

54. Allen JH, de Moore GM, Heddle R et al. Can- nabinoid hyperemesis: cyclical hyperemesis in association with chronic cannabis abuse. Gut 2004;53:1566-70.

55. Simonetto DA, Oxentenko AS, Herman ML et al. Cannabinoid hyperemesis: a case series of 98 patients. Mayo Clin Proc 2012;87:114-9.

56. Khattar N, Routsolias JC. Emergency depart- ment treatment of cannabinoid hyperemesis syndrome: a review. Am J Ther 2018;25:e357-61.

57. Nourbakhsh M, Miller A, Gofton J et al. Can- nabinoid hyperemesis syndrome: reports of fatal cases. J Forensic Sci 2019;64:270-4.

58. Jouanjus E, Lapeyre-Mestre M, Micallef J. Can- nabis use: signal of increasing risk of serious cardiovascular disorders. J Am Heart Assoc 2014; 3:e000638.

59. Arora S, Goyal H, Aggarwal P et al. ST-segment elevation myocardial infarction in a 37-year-old man with normal coronaries – it is not always cocaine! Am J Emerg Med 2012;30:2091.e3-5.

60. Casier I, Vanduynhoven P, Haine S et al. Is re- cent cannabis use associated with acute coro- nary syndromes? An illustrative case series. Acta Cardiol 2014;69:131-6.

61. Hodcroft CJ, Rossiter MC, Buch AN. Cannabis- associated myocardial infarction in a young man with normal coronary arteries. J Emerg Med 2014;47:277-81.

62. Aronow W, Cassidy J. Effect of marihuana and placebo marihuana smoking on angina pecto- ris. N Engl J Med 1974;291:65-7.

63. Mittleman MA, Lewis R, Maclure M et al. Trig- gering myocardial infarction by marijuana. Cir- culation 2001;103:2805-9.

64. Mukamal K, Maclure M, Muller J et al. An ex- ploratory prospective study of marijuana use and mortality following acute myocardial in- farction. Am Heart J 2008;155:465-70.

65. Frost L, Mostofsky E, Rosenbloom JI et al. Mari- juana use and long-term mortality among sur- vivors of acute myocardial infarction. Am Heart J 2013;165:170-5.

66. Aldington S, Williams M, Nowitz M et al. Effects of cannabis on pulmonary structure, function and symptoms. Thorax 2007;62:1058-63.

67. Bloom J, Kaltenborn W, Paoletti P et al. Res- piratory effects of non-tobacco cigarettes. BMJ 1987;295:1516-8.

68. Moore BA, Augustson EM, Moser RP et al. Res- piratory effects of marijuana and tobacco use in a U.S. sample. J Gen Intern Med 2005;20:33-7.

69. Tan WC, Lo C, Jong A et al. Marijuana and chronic obstructive lung disease: a population- based study. Can Med Assoc J 2009;180:814-20.

70. Tashkin DP, Coulson AH, Clark VA et al. Respira- tory symptoms and lung function in habitual heavy smokers of marijuana alone, smokers of marijuana and tobacco, smokers of tobacco

186 World Psychiatry 19:2 - June 2020

a lone, and non-smokers. Am Rev Respir Dis 1987;135:209-16.

71. Taylor DR, Poulton R, Moffitt T et al. The respir- atory effects of cannabis dependence in young adults. Addiction 2000;95:1669-77.

72. Hancox RJ, Shin HH, Gray AR et al. Effects of quitting cannabis on respiratory symptoms. Eur Respir J 2015;46:80-7.

73. Kempker JA, Honig EG, Martin GS. The effects of marijuana exposure on expiratory airflow. A study of adults who participated in the U.S. Na- tional Health and Nutrition Examination Study. Ann Am Thorac Soc 2015;12:135-41.

74. Berthiller J, Straif K, Boniol M et al. Canna- bis smoking and risk of lung cancer in men: a pooled analysis of three studies in Maghreb. J Thorac Oncol 2008;3:1398-403.

75. Zhang LR, Morgenstern H, Greenland S et al. Cannabis smoking and lung cancer risk: pooled analysis in the International Lung Cancer Con- sortium. Int J Cancer 2015;136:894-903.

76. Gurney J, Shaw C, Stanley J et al. Cannabis expo- sure and risk of testicular cancer: a systematic review and meta-analysis. BMC Cancer 2015;15: 897.

77. Smart R, Pacula RL. Early evidence of the im- pact of cannabis legalization on cannabis use, cannabis use disorder, and the use of other sub- stances: findings from state policy evaluations. Am J Drug Alcohol Abuse 2019;45:644-63.

78. Pacula RL, Kilmer B, Wagenaar AC et al. Devel- oping public health regulations for marijuana: lessons from alcohol and tobacco. Am J Public Health 2014;104:1021-8.

79. Pacula RL. Examining the impact of marijuana legalization on marijuana consumption: in- sights from the economics literature. Santa Monica: RAND Corporation, 2010.

80. Kilmer B, Caulkins JP, Pacula RL et al. Altered state? Assessing how marijuana legalization in California could influence marijuana con- sumption and public budgets. Santa Monica: RAND Drug Policy Research Center, 2010.

81. Cerdá M, Mauro C, Hamilton A et al. Association between recreational marijuana legalization in the United States and changes in marijuana use and cannabis use disorder from 2008 to 2016. JAMA Psychiatry 2020;77:165-71.

82. Everson EM, Dilley JA, Maher JE et al. Post-le- galization opening of retail cannabis stores and adult cannabis use in Washington State, 2009- 2016. Am J Public Health 2019;109:1294-301.

83. Cerdá M, Wall M, Feng T et al. Association of state recreational marijuana laws with adoles- cent marijuana use. JAMA Pediatr 2017;171: 142-9.

84. Kerr WC, Ye Y, Subbaraman MS et al. Changes in marijuana use across the 2012 Washington State recreational legalization: is retrospective assessment of use before legalization more ac- curate? J Stud Alcohol Drugs 2018;79:495-502.

85. Darnell AJ, Bitney K. I-502 evaluation and benefit-cost analysis: second required report. Olympia: Washington State Institute for Public Policy, 2017.

86. Anderson DM, Hansen B, Rees DI et al. Asso- ciation of marijuana laws with teen marijuana

use: new estimates from the Youth Risk Behav- ior Surveys. JAMA Pediatr 2019;173:879-81.

87. Dilley JA, Richardson SM, Kilmer B et al. Preva- lence of cannabis use in youths after legal iza- tion in Washington State. JAMA Pediatr 2019; 173:192-3.

88. Wang GS, Hall K, Vigil D et al. Marijuana and acute health care contacts in Colorado. Prev Med 2017;104:24-30.

89. Davis JM, Mendelson B, Berkes JJ et al. Public health effects of medical marijuana legalization in Colorado. Am J Prev Med 2016;50:373-9.

90. Delling FN, Vittinghoff E, Dewland TA et al. Does cannabis legalisation change healthcare utilisation? A population-based study using the healthcare cost and utilisation project in Colo- rado, USA. BMJ Open 2019;9:e027432.

91. Sokoya M, Eagles J, Okland T et al. Patterns of facial trauma before and after legalization of marijuana in Denver, Colorado: a joint study be- tween two Denver hospitals. Am J Emerg Med 2018;36:780-3.

92. Heard K, Monte AA, Hoyte CO. Brief commen- tary: consequences of marijuana – observa- tions from the emergency department. Ann Intern Med 2019;170:124.

93. Bhandari S, Jha P, Lisdahl KM et al. Recent trends in cyclic vomiting syndrome-associated hospitalisations with liberalisation of cannabis use in the state of Colorado. Intern Med J 2019; 49:649-55.

94. Monte AA, Zane RD, Heard KJ. The implica- tions of marijuana legalization in Colorado. JAMA 2015;313:241-2.

95. Calcaterra SL, Hopfer CJ, Keniston A et al. Changes in healthcare encounter rates possibly related to cannabis or alcohol following legalization of recreational marijuana in a safety-net hospital: an interrupted time series analysis. J Addict Med 2019;13:201-8.

96. Hall KE, Monte AA, Chang T et al. Mental health-related emergency department visits associated with cannabis in Colorado. Acad Emerg Med 2018;25:526-37.

97. Richards JR, Smith NE, Moulin AK. Uninten- tional cannabis ingestion in children: a system- atic review. J Pediatr 2017;190:142-52.

98. Koski L. Retail marijuana product manufactur- ing, packaging, and labeling compliance guid- ance. Lakewood: Marijuana Enforcement Di- vision, 2017.

99. Whitehill JM, Harrington C, Lang CJ et al. Inci- dence of pediatric cannabis exposure among children and teenagers aged 0 to 19 years be- fore and after medical marijuana legalization in Massachusetts. JAMA Netw Open 2019;2: e199456.

100. Chung C, Salottolo K, Tanner A, et al. The im- pact of recreational marijuana commercializa- tion on traumatic injury. Inj Epidemiol 2019;6: 3.

101. Aydelotte JD, Brown LH, Luftman KM et al. Crash fatality rates after recreational marijuana legalization in Washington and Colorado. Am J Public Health 2017;107:1329-31.

102. Sevigny EL. The effects of medical marijuana laws on cannabis-involved driving. Accid Anal

Prev 2018;118:57-65. 103. Lane TJ, Hall W. Traffic fatalities within US

states that have legalized recreational canna- bis sales and their neighbours. Addiction 2019; 114:847-56.

104. Jouanjus E, Leymarie F, Tubery M et al. Can- nabis-related hospitalizations: unexpected serious events identified through hospital data- bases. Br J Clin Pharmacol 2011;71:758-65.

105. Wolff V, Armspach JP, Lauer V et al. Ischaemic strokes with reversible vasoconstriction and without thunderclap headache: a variant of the reversible cerebral vasoconstriction syndrome? Cerebrovasc Dis 2015;39:31-8.

106. Wolff V, Lauer V, Rouyer O et al. Cannabis use, ischemic stroke, and multifocal intracranial vasoconstriction: a prospective study in 48 con- secutive young patients. Stroke 2011;42:1778-80.

107. Plunk AD, Peglow SL, Harrell PT et al. Youth and adult arrests for cannabis possession after decriminalization and legalization of cannabis. JAMA Pediatr 2019;173:763-9.

108. US Substance Abuse and Mental Health Ser- vices Administration. N-SSATS quick statistics state profiles. Rockville: Substance Abuse and Mental Health Services Administration, Center for Behavioral Health Statistics and Quality, 2015.

109. Becker J, Schaub MP, Gmel G et al. Cannabis use and other predictors of the onset of daily cigarette use in young men: what matters most? Results from a longitudinal study. BMC Public Health 2015;15:1-10.

110. Males M, Buchen L. Reforming marijuana laws: which approach best reduces the harms of crim- inalization? A five state analysis. San Francisco: Centre on Juvenile and Criminal Justice, 2014.

111. Black P, Joseph LJ. Still dazed and confused: midlife marijuana use by the baby boom gen- eration. Deviant Behav 2014;35:822-41.

112. Han BH, Sherman S, Mauro PM et al. Demo- graphic trends among older cannabis users in the United States, 2006-13. Addiction 2017;112:516- 25.

113. Bachman J, Wadsworth K, O’Malley P et al. Smoking, drinking, and drug use in young adult- hood: the impacts of new freedoms and new responsibilities. Mahwah: Lawrence Erlbaum, 1997.

114. Terry-McElrath YM, Patrick ME, O’Malley PM et al. The end of convergence in developmental patterns of frequent marijuana use from ages 18 to 30: an analysis of cohort change from 1976- 2016. Drug Alcohol Depend 2018;191:203-9.

115. Shover CL, Humphreys K. Six policy lessons relevant to cannabis legalization. Am J Drug Alcohol Abuse 2019;45:698-706.

116. Fischer B, Russell C, Sabioni P et al. Lower-risk cannabis use guidelines: a comprehensive up- date of evidence and recommendations. Am J Public Health 2017;107:e1-12.

DOI:10.1002/wps.20735