During the past 2 decades, nearly half of U.S. states implemented policies that sanction marijuana use for medical purposes. Researchers have been hard put, however, to draw firm conclusions about the policies’ public health ramifications. Now, NIDA-supported researchers have found that providing legal and practical access to marijuana may have both positive and negative impacts.

Image Legalized medical marijuana dispensaries are associated with both positive and negative impacts on public health.

Economists Dr. David Powell and Dr. Rosalie Pacula at the RAND Corporation, in Santa Monica, California, and Dr. Mireille Jacobson at the University of California, Irvine (UC-I) studied three medical marijuana policies (see Recommended, Not Prescribed). They found that the policies, despite their common motivation, have had varied, and sometimes offsetting, indirect effects on substance use and related problems. The most striking finding was that legally protected marijuana dispensaries (LMDs) were associated with lower rates of dependence on prescription opioids, and deaths due to opioid overdose, than would have been expected based on prior trends. On the other side of the ledger, however, LMDs also were associated with higher rates of recreational marijuana use and increased potency of illegal marijuana.

The Opioid Connection

Between 2004 and 2014, seventeen states provided legal protection to dispensaries. In these states, patients who meet eligibility requirements for medical marijuana had ready and safe access to the drug. In contrast, patients in states that allowed doctors to recommend marijuana but did not have LMDs may have turned to illicit or quasi-illicit sources, and feared legal jeopardy, to obtain the drug.

Dr. Powell and his co-investigators compared rates of opioid-related treatment admissions and mortality rates in states with and without LMDs using data from the annually compiled Treatment Episodes Data Set (TEDS) and the National Vital Statistics System, respectively. Their analysis revealed that states with LMDs had lower opioid-overdose mortality rates and fewer admissions to treatment for opioid addiction than they would have had without the dispensaries. The estimated sizes of the reductions were 16 to 31 percent in mortality due to prescription opioid overdoses, and 28 to 35 percent in admissions for treatment of opioid addiction. This latter reduction was steeper, up to 53 percent, among patients who entered treatment independently of the criminal justice system. The researchers also noted a trend whereby the longer LMDs were in place, the more the incidence of opioid-related problems declined.

To account for these findings, the RAND/UC-I team speculates that some patients with chronic pain may find that marijuana affords valuable analgesia with more acceptable side effects than opioids. LMDs will make it easier for such patients to obtain and use marijuana, and so reduce their reliance on opioids to manage their pain. Another possible explanation, the researchers suggest, is that where LMDs exist, recreational drug users may find marijuana simpler and less risky to divert than prescription opioids. Both scenarios could reduce a population’s exposure to opioid medications and the associated problems of overdose and addiction.

A Downside of Availability

Using data from the TEDS and the Longitudinal Survey of Youth, the researchers found that LMDs were also associated with higher:

Recreational marijuana use by adults

Treatment admissions for marijuana use and dependence among adults and youth

Potency of illegal marijuana

Dr. Pacula explains the last finding: “The marijuana available in dispensaries can have THC [tetrahydrocannabinol, the psychoactive ingredient in marijuana] content well above 20 percent—even higher in the concentrates—as opposed to the 3 percent to 5 percent that is typical of the wild plant.” To compete, illegal marijuana dealers have apparently begun to increase the THC content of their products. This development is troubling, Dr. Pacula says, because “Higher potency may result in increased impairment, with potential implications for drugged driving and drug-induced psychoses.”

The Bigger Picture

Dr. Pacula characterizes her team’s findings as intriguing and says that any indication that a policy might mitigate the ongoing surge in opioid dependence and mortality deserves attention. However, she cautions that it is premature to conclude that LMDs will have a beneficial effect going forward.

First, LMDs’ effects on substance use will depend on the overall regulatory context in which they function. That context is changing, as some states have recently passed medical marijuana laws that impose tighter safeguards against misuse than pertained during the period studied by the RAND/UC-I team. For example, some states require that physicians who recommend marijuana and patients who obtain the drug register and certify that they have a bona fide physician-patient relationship. Other states allow only a limited number of dispensaries or require dispensaries to report marijuana sales in the state prescription drug-monitoring programs. Such requirements may reduce some physicians’ readiness to recommend the drug and make it harder for people to divert marijuana from LMDs for self-treatment of pain or for recreational use.

Second, LMDs’ association with increased use of recreational marijuana is likely to offset, at least partially, any opioid-related benefits. Dr. Pacula notes that many people are looking for affordable substances that they can use to get high. “When marijuana becomes readily available, this population will misuse it, and problems can ensue.” The problems could be exacerbated if the relationship between LMDs and higher potency marijuana continues to hold—potentially setting the stage for more injuries and deaths in motor vehicle and other accidents.

Dr. Pacula points out, as well, that marijuana policies may indirectly influence use of substances besides opioids. While the scientific evidence regarding the relationship between marijuana and alcohol use remains mixed, the evidence regarding the link between marijuana and tobacco use is quite clear: Users of marijuana generally also use tobacco. So, Dr. Pacula says, “Any assessment of the overall net benefit of LMDs needs to consider impacts not just on marijuana and opioids, but also on tobacco and other substances that generate disease and mortality.”

More Research Is Needed

Dr. Pacula says, “It would be valuable to repeat this study in 4 or 5 years, when states’ recent, often more restrictive, medical marijuana laws can be evaluated. We need to give the data on marijuana and opioid use time to catch up with the policies that have been enacted.” She expects that such an analysis would produce different results and shed additional light on how LMDs and other medical marijuana policies, singly and together, shape population behaviors, substance abuse, and other public health outcomes.

Dr. Bethany Deeds, health science administrator in NIDA’s Epidemiology Research Branch, says, “This work analyzes several years of data and thus looks through a large window at the effects of marijuana dispensaries. The researchers used advanced statistical methods, like difference-in-differences models and synthetic control models, and measured the social environments and mechanisms behind the laws in sophisticated ways to yield robust findings.”

Dr. Deeds continues, “The RAND report is one piece of evidence on the social, behavioral, and public health impacts of new marijuana policies. Although medical marijuana dispensaries may correlate with a reduction in opioid misuse, there are other consequences to consider.”

Dr. Pacula concurs. “Before we finalize any decisions, we need to consider how all the policies in place and under consideration will work together, and know how they will affect public health overall, and not simply with respect to a single drug of abuse.”

Recommended, Not Prescribed Federal regulations prohibit most physicians from prescribing marijuana, but nearly half of the states permit doctors to recommend the drug for certain medical conditions. Beyond that commonality, however, these states’ policies vary widely. The lists of qualifying conditions differ from state to state. So, too, do the legal protections offered to marijuana vendors and customers, requirements for the registration of distributors and patients, and the regulation of marijuana home cultivation. Few policies enable physicians to control the quantity, potency, or frequency of marijuana purchases or how patients take it, which further increases variability in how medical marijuana is used and affects patients. Dr. Pacula and colleagues compared rates of marijuana and prescription opioid-related use and problems, from 1999 and 2014, in states that allowed and didn’t allow physicians to recommend marijuana, and in states with and without policies that: Established LMDs.

Required physicians and/or patients to register to prescribe and use marijuana.

Allowed home cultivation of marijuana plants. The results linked LMDs to decreased opioid-related treatment admissions and overdose deaths, and to increased recreational marijuana use and treatment admissions. Neither of the other two policies was consistently associated with these outcomes.

This work was supported by NIH grant DA032693.

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