The cannabis-policy landscape is undergoing dramatic change. Although many jurisdictions have removed criminal penalties for possessing small amounts of cannabis and more than half of U.S. states allow physicians to recommend it to patients, legalizing the supply and possession of cannabis for nonmedical purposes is a very different public policy. Since the November 2016 election, 20% of the U.S. population lives in states that have passed ballot initiatives to allow companies to sell cannabis for any reason and adults 21 or older to purchase it. Although other states may move toward legalization, uncertainty abounds because of the federal prohibition on cannabis. The Obama administration tolerated these state laws; it’s unclear what the Trump administration will do.

There is also tremendous uncertainty about the net effect of cannabis legalization on public health.1 Most adults who occasionally use cannabis find it pleasurable and don’t experience substantial problems. There is a growing body of research on the medical benefits of consuming cannabis flowers or extracts,1,2 and legalization should make it easier to study the therapeutic potential and allow access for patients who could benefit.

…

Fourth, given the dearth of information about the consequences associated with high-potency cannabis products and our inability to measure cannabis impairment, risk-averse policymakers may consider initially limiting access to certain types of products or imposing a cap on products’ THC content. Another option, offered by Stanford social psychologist Robert MacCoun and others, is to tax cannabis according to THC content, thereby giving jurisdictions a lever to nudge users toward lower-potency products.