The claim that medical cannabis laws reduce opioid deaths reversed when extended through 2017
Replicating a landmark 2014 study through 2017, the previously reported association between medical cannabis laws and reduced opioid deaths reversed from -21% to +23%, suggesting the original finding was likely spurious.
Quick Facts
What This Study Found
Extending the Bachhuber et al. (2014) analysis from 2010 to 2017 using identical methods, the association between medical cannabis laws and opioid overdose mortality reversed from -21% to +23%. Neither recreational cannabis laws nor low-THC cannabis laws were associated with opioid mortality changes.
Key Numbers
Original finding (1999-2010): -21% opioid mortality. Extended finding (1999-2017): +23% opioid mortality. Medical cannabis used by about 2.5% of US population. Neither recreational nor low-THC laws showed association.
How They Did This
Replication and extension of Bachhuber et al. (2014) using the same state-level panel regression methods through 2017. Analyzed associations between medical cannabis law adoption and opioid analgesic overdose mortality rates.
Why This Research Matters
The original 2014 study was widely cited by the cannabis industry and advocates as evidence that medical cannabis reduces opioid deaths. This reversal demonstrates the danger of drawing causal conclusions from ecological correlations.
The Bigger Picture
This is a cautionary tale about cherry-picking time periods in policy research. The opioid crisis has its own trajectory driven by factors far more powerful than cannabis access, making it implausible that cannabis policy explains large swings in overdose mortality.
What This Study Doesn't Tell Us
Ecological (state-level) analysis cannot capture individual-level substitution. The reversal itself does not prove medical cannabis increases opioid deaths. The authors interpret the association in both directions as likely spurious.
Questions This Raises
- ?Why did the association reverse?
- ?Is it because more states adopted cannabis laws during the most severe phase of the opioid crisis?
- ?Can individual-level studies better capture cannabis-opioid substitution effects?
Trust & Context
- Key Stat:
- Association reversed from -21% to +23% with extended data
- Evidence Grade:
- Strong: direct replication using identical methods with extended data, published in PNAS.
- Study Age:
- Published in 2019.
- Original Title:
- Association between medical cannabis laws and opioid overdose mortality has reversed over time.
- Published In:
- Proceedings of the National Academy of Sciences of the United States of America, 116(26), 12624-12626 (2019)
- Authors:
- Shover, Chelsea L(2), Davis, Corey S(3), Gordon, Sanford C, Humphreys, Keith
- Database ID:
- RTHC-02293
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Does this mean medical cannabis increases opioid deaths?
No. The authors argue that neither the original negative association nor the reversed positive association is likely causal. With only 2.5% of the population using medical cannabis, it is implausible to have large effects on population-level opioid mortality.
Should we stop researching cannabis for pain?
No. Individual-level research on cannabis as an opioid alternative should continue. What should stop is the claim that state-level cannabis laws have been proven to reduce opioid overdose deaths.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-02293APA
Shover, Chelsea L; Davis, Corey S; Gordon, Sanford C; Humphreys, Keith. (2019). Association between medical cannabis laws and opioid overdose mortality has reversed over time.. Proceedings of the National Academy of Sciences of the United States of America, 116(26), 12624-12626. https://doi.org/10.1073/pnas.1903434116
MLA
Shover, Chelsea L, et al. "Association between medical cannabis laws and opioid overdose mortality has reversed over time.." Proceedings of the National Academy of Sciences of the United States of America, 2019. https://doi.org/10.1073/pnas.1903434116
RethinkTHC
RethinkTHC Research Database. "Association between medical cannabis laws and opioid overdos..." RTHC-02293. Retrieved from https://rethinkthc.com/research/shover-2019-association-between-medical-cannabis
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.