Cannabis legalization made it harder to keep patients enrolled in medical cannabis research
After Canada legalized recreational cannabis, retention in a prospective medical cannabis study dropped significantly, with patients who could access cannabis elsewhere less likely to stay enrolled.
Quick Facts
What This Study Found
Legalization of non-medical cannabis was associated with significantly lower odds of study retention (AOR 0.28, 95% CI 0.18-0.41). Baseline opioid use also predicted dropout, while higher psychological health scores and anti-seizure medication use predicted staying in the study.
Key Numbers
1,011 participants; 287 patient-years of data; 72% retained at 3 months; 41.4% at 6 months; post-legalization retention AOR 0.28; opioid use AOR 0.62; anti-seizure medication AOR 1.91
How They Did This
The Tilray Observational Patient Study followed 1,011 Canadian medical cannabis patients across multiple sites from 2016 to 2019. Kaplan-Meier survival analysis and logistic regressions assessed factors associated with retention at 3 and 6 months.
Why This Research Matters
High dropout rates threaten the validity of cannabis research. Understanding why patients leave studies is critical for designing future trials that produce reliable evidence on medical cannabis benefits and harms.
The Bigger Picture
This study reveals an ironic challenge: legalizing cannabis for recreational use may actually undermine the medical research needed to understand cannabis as medicine, as patients no longer need to stay in studies to access the product.
What This Study Doesn't Tell Us
Convenience sample limits generalizability. Self-reported cannabis use data. Industry-sponsored study (Tilray). Cannot fully separate legalization effects from other temporal factors.
Questions This Raises
- ?How can researchers design studies that retain participants when cannabis is freely available?
- ?Does dropout bias systematically overestimate or underestimate medical cannabis benefits?
- ?Would compensating participants adequately solve the retention problem?
Trust & Context
- Key Stat:
- 72% drop in retention odds after recreational legalization
- Evidence Grade:
- Multi-site prospective study with survival analysis, though convenience sampling and industry sponsorship limit generalizability.
- Study Age:
- Published in 2021 using data from 2016-2019.
- Original Title:
- The impact of non-medical cannabis legalization and other exposures on retention in longitudinal cannabis research: a survival analysis of a prospective study of Canadian medical cannabis patients.
- Published In:
- Journal of cannabis research, 3(1), 34 (2021)
- Authors:
- Lucas, Philippe(11), Boyd, Susan(4), Milloy, M-J(17), Walsh, Zach
- Database ID:
- RTHC-03302
Evidence Hierarchy
Enrolls participants and follows them forward in time.
What do these levels mean? →Frequently Asked Questions
Why did patients drop out after legalization?
The study suggests patients no longer needed to stay enrolled in a medical cannabis study to access cannabis, since they could buy it legally through recreational dispensaries or the illicit market.
What kind of patients stayed in the study?
Patients with higher psychological health scores and those using anti-seizure medications were more likely to remain enrolled, possibly because they were more motivated by medical outcomes rather than just access.
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Cite This Study
https://rethinkthc.com/research/RTHC-03302APA
Lucas, Philippe; Boyd, Susan; Milloy, M-J; Walsh, Zach. (2021). The impact of non-medical cannabis legalization and other exposures on retention in longitudinal cannabis research: a survival analysis of a prospective study of Canadian medical cannabis patients.. Journal of cannabis research, 3(1), 34. https://doi.org/10.1186/s42238-021-00089-7
MLA
Lucas, Philippe, et al. "The impact of non-medical cannabis legalization and other exposures on retention in longitudinal cannabis research: a survival analysis of a prospective study of Canadian medical cannabis patients.." Journal of cannabis research, 2021. https://doi.org/10.1186/s42238-021-00089-7
RethinkTHC
RethinkTHC Research Database. "The impact of non-medical cannabis legalization and other ex..." RTHC-03302. Retrieved from https://rethinkthc.com/research/lucas-2021-the-impact-of-nonmedical
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.