Medical cannabis was proposed as a solution to the U.S. opioid overdose crisis since a study by Bachhuber et al. found that from 1999 to 2010, states with medical cannabis laws had slower increases in deaths from opioid overdose.
However, a new study shows that the original findings failed to hold over the longer term, after researchers extended the analysis through 2017. Moreover, the association between state medical cannabis laws and opioid overdose mortality reversed from −21% to +23%, and it remained positive even after accounting for recreational cannabis laws.
The researchers say there is no evidence to suggest that either broader (recreational) or more restrictive (low-tetrahydrocannabinol) cannabis laws were associated with changes in opioid overdose mortality. Also, it is unlikely that medical cannabis—used by about 2.5% of the U.S. population—has large conflicting effects on opioid overdose mortality.
If the endpoint of the current analysis had been between 2008 and 2012, say the researchers, results would have been comparable to Bachhuber et al. But by 2013, the association had become equivocal; and by 2017, it had reversed to such a degree that a study conducted that year “might have led some to conclude that medical cannabis laws were compounding opioid overdose mortality.”
Under the study model, states with highly restrictive medical cannabis laws would be expected to have a weaker association than states with comprehensive laws, and states with recreational cannabis would be expected to have a stronger association. But the results did not support this. After adjusting for more and less restrictive types of cannabis law, states with comprehensive laws still had a positive association with opioid overdose mortality.
Research into the therapeutic potential of cannabis should continue, concluded the study authors, but anticipating reductions in opioid overdose deaths by enacting medical cannabis laws is not warranted.
Source: Proceedings of the National Academy of Sciences, June 10, 2019