In the US, federal law has severely restricted our ability to study any potential medical properties of cannabis. But, given some limited studies and a lot of anecdotal stories, a number of states have gone ahead and legalized medical marijuana. This has allowed some population-level studies of what’s going on in the states, but those have faced additional complications, like rules that differ from state to state and an ongoing legalization of recreational use confusing the picture.

Just how confusing all this can be was driven home this week by the release of a paper that suggests that one of medical marijuana’s greatest successes was illusory. A couple of early studies indicated that states that had legalized medical marijuana use saw drops in opioid-related deaths. The new research replicates those results but finds that the trend has reversed in recent years, with those states now seeing increased deaths. While the new study’s authors suggest the initial results were spurious, others suggest that the shifting legal landscape and changes in drug abuse may have driven the change.

What does everyone agree upon?