United States marijuana legalization and opioid mortality epidemic during 2010-2020 and pandemic implications.

Background: The hypothesis that marijuana availability reduces opioid mortality merits more complete testing, especially in a country with the world's highest opioid death rate and 2nd highest cannabis-use-disorder prevalence.

Methods: The United States opioid mortality rate was compared in states and District of Columbia that had implemented marijuana legalization with states that had not, by applying joinpoint methodology to Centers for Disease Control and Prevention data. Variables included race/ethnicity and fentanyl-type opioids (fentanyls).

Results: After the same rates during 2010-2012, the opioid mortality rate increased more rapidly in marijuana-legalizing than non-legalizing jurisdictions (2010-2020 annual pairwise comparison p = 0.003 for all opioids and p = 0.0004 for fentanyls). During the past decade, all four major race/ethnicities in the U.S. had evidence for a statistically-significant greater increase in opioid mortality rates in legalizing than non-legalizing jurisdictions. Among legalizing jurisdictions, the greatest mortality rate increase for all opioids was in non-Hispanic blacks (27%/year, p = 0.0001) and for fentanyls in Hispanics (45%/year, p = 0.0000008). The greatest annual opioid mortality increase occurred in 2020, the first year of the COVID-19 pandemic, with non-Hispanic blacks having the greatest increase in legalizing vs. non-legalizing opioid-death-rate difference, from 32% higher in legalizing jurisdictions in 2019 to more than double in 2020.

Conclusions: Instead of supporting the marijuana protection hypothesis, ecologic associations at the national level suggest that marijuana legalization has contributed to the U.S.'s opioid epidemic in all major races/ethnicities, and especially in blacks. If so, the increased use of marijuana during the 2020-2022 pandemic may thereby worsen the country's opioid crisis.