A new working paper from the National Bureau of Economic Research contains some inconvenient news for the rosy worldview of those who claim that marijuana is a completely harmless drug.

The paper reviews data on opioid and marijuana use and makes two key findings — first, that “medical marijuana, particularly when available through retail dispensaries, is associated with higher opioid mortality.” The second finding is that data “for recreational marijuana, while less reliable, also suggest that retail sales through dispensaries are associated with greater death rates relative to the counterfactual of no legal cannabis.”