Legal, policy changes can lead to shifts in use of medical marijuana

The findings, published online in the journal Drug and Alcohol Dependence, suggest a possible "participation elasticity" that could inform future discussions around medical marijuana provisions at both the state and federal level. Medical marijuana is legal to varying degrees in 23 states and the District of Columbia.

In one finding, researchers determined that medical marijuana use in the states of Colorado, Montana and Michigan rose dramatically in 2009 when the federal government announced that it was making medical marijuana prosecutions a low priority. (In the previous administration, the federal government prosecuted medical marijuana users along with recreational users, since marijuana was -- as it is today -- against federal law.) By contrast, medical marijuana participation rose little in states the expressly prohibited dispensaries, such as Alaska, Rhode Island and Vermont.

The federal policy change led to an increase in the number of medical marijuana dispensaries, which may have led to an increase in medical marijuana participation. When Colorado and Montana responded with regulations aimed at limiting dispensaries, their numbers fell, as did the number of medical marijuana registrants in these states.

"At one point, it seemed like there were more dispensaries than Starbucks in some cities," says study author Brian Fairman, PhD, a postdoctoral fellow in the Bloomberg School's Department of Mental Health. "Then when the number of dispensaries dropped, so did the number of registrants. Interestingly, after Colorado legalized recreational marijuana use, the rates of medical marijuana participation held steady, perhaps because sales taxes are lower for medical marijuana, so it's more affordable."

California became the first state to allow medical marijuana use in 1996. Since then, another 22 states and the District of Columbia approved medical marijuana use. An estimated 2.7 million people use medical marijuana, according to data based on a household survey from the U.S. National Survey on Drug Use and Health. However, state registries log only about 440,000 medical marijuana users, in part because registration is voluntary in some states, including California, so many patients do not register.

The rules governing the practice vary from state to state, with some allowing dispensaries and some not and some only allowing cannabis that is ingested (versus smoked or inhaled). Most patients who use medical marijuana do so for pain relief.

For this analysis, only 13 states, along with the District of Columbia, with medical marijuana registries that had data available over time were included. The states analyzed were Alaska, Arizona, Colorado, Connecticut, Hawaii, Michigan, Montana, Nevada, New Jersey, New Mexico, Oregon, Rhode Island and Vermont.

Other findings include:

• Among the eight states that report differences by age, medical marijuana patients under the age 18 make up less than 1 percent of medical marijuana patients. However, since June 2013 the number of minor patients in Colorado has increased significantly, possibly due to parents moving to the state to take advantage of the state's dispensary market.
• In most states with available data, medical marijuana participants tend to be in their 50s, which is consistent with the "baby boomer" generation that had high rates of marijuana use during the mid-1970s. However, Colorado and Arizona have larger proportions of medical marijuana participants between the ages of 18 and 30.
• In states that report differences in medical marijuana by gender, men are more likely than women to register for medical marijuana, -- between 60 and 70 percent are men -- but there is evidence that women may be catching up over time.

The benefits of medical marijuana are little understood, largely because there is scant research, which is complicated by required clearance from the U.S. Drug Enforcement Administration.

"Marijuana policy is at a crossroads," Fairman says. "It's especially important that policymakers and the public understand what might contribute to trends in medical marijuana use, considering the number of people who seek it for chronic pain and also how it might interplay with recreational use as more states legalize recreational marijuana."

"Trends in registered medical marijuana participation across 13 U.S. states and District of Columbia" was written by Brian J. Fairman, PhD.

The author acknowledges funding support by the National Institutes of Health under the Ruth L. Kirschstein National Research Service Award (T32DA007292) from the National Institute on Drug Abuse.