The implementation of medical marijuana policies did not have any significant associations with hospitalizations related to marijuana dependence or abuse. However, it was associated with a 23% reduction in hospitalizations related to opioid dependence or abuse and a 13% reduction in hospitalizations related to OPR overdose . In Table 2, the first column for each outcome variable evaluates the indicator of medical marijuana dispensaries. Relative to generic implementation of medical marijuana legalization, the operation of medical marijuana dispensaries had comparable associations with hospitalizations related to opioid dependence or abuse and OPR overdose . The second column for each outcome variable reports results including both the indicator of medical marijuana policy and the indicator of medical marijuana dispensaries. Medical marijuana dispensaries alone did not have any independent associations with any hospitalization outcomes after indicators for medical marijuana policy implementation were also included in the regressions. In Table 3, we explored if any policy effects could be detected in the periods prior to the implementation year of medical marijuana policies. We found no evidence that hospitalization rates of any category differed between states adopting and non-adopting medical marijuana policies in the pre-policy periods. Table 3 also assesses the presence of dynamic policy effects after the implementation year. We found that the reduction in hospitalizations related to opioid dependence or abuse was most salient after 1 year of policy implementation , whereas the reduction in hospitalizations related to OPR overdose was observed in the third year after policy implementation . With respect to other policy and socioeconomic covariates, uninsured rate was associated with increased OPR overdose hospitalizations. Other covariates including marijuana decriminalization,weed trimming tray prescription drug monitoring program, and pain management clinic regulations were generally not associated with any hospitalization outcomes.

Using state-level administrative hospitalization data during 1997–2014, we found no convincing evidence that the implementation of medical marijuana policies was associated with a subsequent increase in marijuana-related hospitalizations. This result was robust to the key policy dates defined in different ways. In conjunction with the studies that demonstrated negative or null associations of medical marijuana policies to substance abuse treatment admissions , suicide rates , and crime rates , our study counters the arguments about the severe health consequences that legalizing medical marijuana may bring to the public health. It should be noted that this study does not necessarily contradict some prior research that reported an increase in marijuana use prevalence in association with medical marijuana policies . It just appears that, even if legalization resulted in an increase in the prevalence, it did not contribute to the severe health consequences that concern the public the most. Whether such findings hold in the long term needs further monitoring and investigations. This study demonstrated significant reductions in OPR-related hospitalizations associated with the implementation of medical marijuana policies. These findings were supported by the recent studies that reported reduced prescription medications , OPR overdose mortality , opioid positivity among young and middle aged fatally injured drivers , and substance abuse treatment admissions in association with medical marijuana legalization. The mechanisms for the causal connections between marijuana and OPR are not clear. As mentioned earlier, using marijuana can lead to either an increase or a reduction in OPR use depending on the use purposes and the underlying assumptions. This study appears to support the hypothesis that patients prescribed with OPR substitute OPR with marijuana, but it is not directly testable in our data. An alternative explanation for the results reported in this study is that states with medical marijuana legalization may also have tough OPR prescription regulations.

However, this hypothesis was not supported by the null associations of OPR prescription regulations estimated in this study. Future empirical evaluations are warranted to explore the use pattern of OPR and marijuana and substantiate the substituting and gateway effects of the two drugs. Consistent with prior research , policy effects reported in this study were not static. We found reductions in OPR-related hospitalizations immediately after the year of policy implementation as well as delayed reductions in the third post-policy year. Nonetheless, the availability of medical marijuana dispensaries was not independently associated with hospitalizations as suggested by other studies . A possible interpretation is that only 1 state in our data legalized medical marijuana but did not have operating medical marijuana dispensaries; a few other states opened medical marijuana dispensaries within only 1–2 years after the legalization of medical marijuana. The lack of variations in policy adoption and timing limited our ability to detect independent effects of detailed policy provisions of medical marijuana legalization. The 300% increase in hospitalization rates related to marijuana is striking. In contrast, the past-month prevalence of marijuana use increased at a much slower rate from 6% in 2002 to 7.5% in 2013 . It is unclear what factors have been driving the huge discrepancies between the trends of use prevalence and the trends of hospitalization rates. Although quite a few states legalized medical marijuana or decriminalized marijuana, this study suggested that they did not contribute to the rise of marijuana-related hospitalizations. One alternative hypothesis is the escalation in marijuana potency , which has tripled from 4% in 1995 to 12% in 2014 in the U.S. . Nonetheless, empirical evidence again did not find any associations between the potency increase and the legalization of medical marijuana . Studies to understand the growing market share of high-potency marijuana and its associations with marijuana-related hospitalizations are urgently needed. The unprecedented increase in OPR-related hospitalization rates and other related health outcomes has become a major public health crisis.

Compared to the limited research on marijuana, OPR abuse and overdose epidemic has been relatively well studied. Despite lack of evidence in this study, prescription drug monitoring programs and pain management clinic regulations have shown promises to tackle the OPR crisis in some other studies . If the causal relationship indicated in this study can be substantiated in future research, medical marijuana legalization and regulation may be considered as an alternative strategy to reduce OPR-related hospitalizations without aggravating the adverse consequences related to marijuana. Our study was subject to several limitations, most of which were related to the data used. First, some states included hospitalization records in the SID from non-community hospitals such as psychiatric facilities and Veterans Affairs hospitals, but some states did not . States may also vary on ICD-9-CM coding practice particularly for drug dependence, abuse, and overdose cases. The coding of opioid dependence or abuse may include heroin cases. The inclusion of state fixed effects should to some extent alleviate these biases in the reporting. Second, the aggregate SID data represented the total number of discharges but not the total number of patients because a patient may be admitted to hospital more than once in a year. The public-use SID were not available before 1997 and not all states participated in the SID during the study period. The findings may not be generalizable to the states that were excluded from this study. Particularly, the results may be inapplicable to California, which has the longest history of medical marijuana legalization as well as the largest population of registered medical marijuana patients and the largest number of medical marijuana dispensaries. Third, although no statistical differences in hospitalization rates between states adopting and non-adopting medical marijuana policies were revealed before policy implementation,cannabis grow setup we cannot rule out policy endogeneity issues that may be caused by time-varying unobserved factors and were not captured by the two-way fixed effects models. In addition, we were not able to examine detailed policy provisions of medical marijuana legalization such as home cultivation and requirement of patient registry because of small sample size and lack of variations. We were not able to assess OPR-related policies that were adopted by a few states most recently, such as requirements of following OPR prescribing guidelines and mandatory checking prescription drug monitoring program data by providers. This limitation, however, is unlikely to influence the study findings significantly because these policies were not adopted until the very end of the study period or after the study period. Finally, the study findings do not apply to recreational marijuana legalization. In fact, the findings are likely to alter if marijuana for recreational purpose is indeed a gateway drug to OPR. Examinations on the most recent regulations of recreational marijuana are warranted.The United Nations recently estimated that the global illegal drug trade is worth at least US$350 billion annually, and illegal drug use remains a major threat to community health and safety.In addition to the range of harm associated with the direct health effects of drugs, including fatal overdose, illegal drug use is also one of the key global drivers of blood-borne disease transmission, in particular HIV infection. Illegal drug markets also contribute to community concerns, such as high rates of violence in settings where the trade proliferates.

In response to the health and social concerns associated with illegal drug use, several UN conventions were organised to control the possession, consumption and manufacture of illegal drugs.As a result, during the last several decades, most national drug control strategies have prioritised drug law enforcement interventions to reduce drug supply, despite recent calls by experts to explore alternative models of drug control, such as systems of drug decriminalisation and legal regulation. Some unintended consequences of this approach, such as record incarceration rates, have been well documented. In addition, a small number of studies assessing aspects of drug supply, measured through indicators of drug price, purity/potency and seizures, have been undertaken to describe the global relationship between these indicators over the long term. However, systematic evaluation of these relationships is still needed to elucidate patterns of drug supply. The present study, therefore, sought to systematically identify international data from publicly available illegal drug surveillance systems to assess long-term estimates of illegal drug supply.The primary outcomes of interest were long-term patterns of illegal drug supply, measured through indicators of price and purity/potency for three major illegal drugs: cannabis, cocaine and opiates . While data on amphetamine-type stimulants exist in some countries , this class of drugs was not included given inconsistent data collection and classification, and fluctuating surveillance periods and overall data quality. A secondary outcome of interest was data on illegal drug seizures in major illegal drug source regions and, major destination markets, as identified by the United Nations Office on Drugs and Crime . These secondary outcome data were used as an additional proxy measure to assess the availability of illegal drugs in specific regions, as has been carried out previously. All outcomes were systematically identified through publicly available illegal drug surveillance systems. Linear-by-linear association trend tests were carried out on annual estimates of all outcomes of interest. Price and purity estimates represent median values for each year, while estimates for seizures represent crude totals of quantity seized. All price estimates are expressed in 2011 USD and are, where possible, adjusted for purity. An online search of surveillance systems monitoring illegal drugs using two a priori defined inclusion criteria was carried out. Search terms included the following: drugs, illicit, illegal, price, purity, potency, surveillance system, government data, longitudinal, annual, estimate. Inclusion/exclusion criteria were as follows: only surveillance systems that included continuous longitudinal assessments of these outcomes of interest for at least 10 years were included because we specifically sought to assess the long-term impact of enforcement-based supply reduction strategies on illegal drug price and purity/ potency. Finally, data extraction was restricted to 1990 and onwards to focus on patterns of supply during recent decades. Data were obtained through online searches of registries of surveillance systems , governmental reports and peer-reviewed publications, through referrals from experts in the field, and through data requests to relevant organisations including the UNODC. All authors had complete access to all data and all had final responsibility to submit for publication. Ethics approval was not required given that we relied exclusively on publicly available data.We identified seven government surveillance systems that met inclusion criteria. Of these, 3 reported on international data, 3 on data from the USA and 1 on data from Australia. One of the longest running surveillance system identified, the US-based Marijuana Potency Monitoring Project, is funded by the US National Institutes of Health and was established in 1975, while the most recent surveillance system was established in 2001 .