A new study by the Stanford School of Medicine titled ” Association between medical cannabis laws and opioid overdose mortality has reversed over time” questions the findings of a widely cited 2014 study that showed states that had legalized medical cannabis experienced fewer deaths from opiate overdoses. The researchers used the same methods as the 2014 study, but found the positive results did not hold up when the time period was extended from 1999-2010 to 1999-2017.
In fact, they found states who had recently passed medical cannabis laws — in the additional seven years, 32 states passed medical cannabis law, including seventeen who passed high CBD laws — actually saw an increase in opioid overdose deaths. Additionally, researchers found no correlation between the level of cannabis restrictions and overdose deaths when comparing states with more restrictive medical cannabis laws to states with recreational cannabis.
However, the researchers said if they had stopped their analysis at 2012, the 2014 findings would have held. They say it was not until 2013 the results became “equivocal.” According to the paper, by 2017 the findings had reversed such that if a study was conducted that year, one could conclude medical cannabis laws contributed to higher opiate mortality rates.
The study was funded by a grant from the National Institute of Health, the Veterans Health Administration, and the Stanford Department of Psychiatry and Behavioral Sciences.
“We find it unlikely that medical cannabis — used by about 2.5% of the US population — has exerted large conflicting effects on opioid overdose mortality. A more plausible interpretation is that this association is spurious. Moreover, if such relationships do exist, they cannot be rigorously discerned with aggregate data. Research into therapeutic potential of cannabis should continue, but the claim that enacting medical cannabis laws will reduce opioid overdose death should be met with skepticism.” — Excerpt from the study
The authors go on to say the 2014 results were widely misinterpreted due to the common assumption that correlation equals causation. They believe that perhaps other factors, such as increased naloxone availability, lower incarceration rates, and better insurance and health services, may have contributed to the lower opioid death rates, not medical cannabis access.
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