Robert MacCoun, a professor of law and a senior fellow at the Freeman Spogli Institute for International Studies, relays the potential risks and benefits of legalizing marijuana. His research focuses on drug policy, and he has written extensively about the effects of marijuana from a legal and health perspective.

California, Massachusetts and Nevada all legalized marijuana in the last election. Does this mean the legalization movement has reached a tipping point?  

If Hillary Clinton had won the election, it would probably feel that way, not because she’s a legalization advocate, but because she’d have bigger fish to fry and would probably continue President Obama’s laissez-faire approach. With the Trump administration’s new cabinet, all bets are off. Still, one in five Americans now live in a state where recreational use of marijuana is legal, and that’s a big market. And as the market grows, the industry’s lobbying clout grows.

What are the health risks post-legalization?

That depends on how much consumption levels increase. There are good reasons to expect marijuana prices to fall, which will increase consumption. Because many people use marijuana without health consequences, I worry less about an increase in the number of people using marijuana than about an increase in the number who use it one or more times daily. There is growing evidence that heavy marijuana use is associated with an increased risk of psychosis. We don’t know if it is a true cause-and-effect relationship; let’s hope it is not. But I think the biggest health threat is dependence, which for marijuana is something like getting stuck in the La Brea tar pits — your world just gets smaller and smaller as you get more dysfunctional.

Robert MacCoun, PhD

How can legalizing states combat these risks?

The good news is that legalization makes possible all sorts of regulatory options that weren’t available under prohibition. States should insist that no marijuana products are to be packaged in a way that entices children. Doses should be standardized, and there should be accurate labeling about the THC content. States should discourage products with high levels of THC, and perhaps encourage products with higher levels of cannabidiol (CBD), an ingredient that seems to counteract some of the harmful effects of THC.

The bad news is that the state ballot initiatives didn’t do much more than give lip service to public health and safety, and industry entrepreneurs are pushing back hard against state regulators. I think the industry is being foolish here — they’ve won eight states but still have 42 states to go. I don’t think they realize how quickly a backlash could emerge if those eight states show rising rates of various adverse outcomes.

Could there be any positive health effects of marijuana use?

Absolutely. There are plenty of lines of evidence suggesting medical benefits for some patients. Intriguingly, several new studies suggest that medical marijuana states may be experiencing reduced levels of opioid use and opioid overdoses. The Catch 22 is that the DEA decided not to reschedule marijuana because there isn’t enough rigorous evidence, but there isn’t enough rigorous evidence because the Feds have made such studies almost impossible to conduct.

Some of the biggest health benefits of marijuana will occur if it turns out that marijuana use is a substitute for binge drinking. There are both physiological and economic reasons to think that might be the case, but while some studies show substitution, others show complementarity. For a researcher, one big benefit of legalization is that it is going to help us finally answer a lot of these research questions.