Colleen Barry is a professor at the Johns Hopkins Bloomberg School of Public Health and co-director of the Johns Hopkins Center for Mental Health and Addiction Policy Research.

While opioid pain relievers offer critical benefits to certain patients, such as those with cancer-related pain, the rise of opioid prescriptions has had devastating public health consequences. The C.D.C. recently urged physicians to be very cautious in prescribing these drugs.

Meanwhile, access to medical marijuana has expanded rapidly — 24 states and D.C. have legalized its broad medical use — and chronic or severe pain is the most common condition reported among those using it. On it's face, this might seem to mirror the rise in prescription opioid use.

Medical marijuana might be safer for chronic pain management than opioids but more research is needed.

But using state-level death certificate data from 1999 to 2010, my colleagues and I found that the annual rate of opioid overdose deaths decreased substantially — by 25 percent on average — following the passage of medical marijuana laws, compared to states that still had bans.

Could medical marijuana be a safer alternative to opioids for chronic pain management? If so, it would potentially reduce harms from opioid medicines.

Our study opened the door to that possibility, but it did not establish the causal mechanisms by which marijuana might influence overdose deaths and was conducted before the massive surge in heroin use and related overdose deaths.

Our study should also not be used to tout the use of marijuana to treat opioid addiction, a particularly upsetting misinterpretation, as the limited evidence available points to the opposite being true: Quitting marijuana may strengthen recovery for individuals with opioid use disorders. Further research is needed.

Similarly, we don't know whether the legalization of marijuana for recreational purposes will have an impact — positive or negative — on nonmedical use of opioids and heroin. Again, evidence is lacking and will likely depend on how recreational marijuana is regulated. But we do know that marijuana dependence has been linked to numerous other negative health consequences independent of opioids.

And if the opioid crisis has taught us anything, it should be that careful regulation, stringent oversight and ongoing evaluation are all absolutely essentially to establishing an environment that protects the public’s health.



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