Objectives: To determine the relative contributions of tetrahydrocannabinol (THC) and cannabidiol (CBD) to patients’ self-ratings of efficacy for common palliative care symptoms. Design: This is an electronic record-based retrospective cohort study. Model development used logistic regression with bootstrapped confidence intervals (CIs), with standard errors clustered to account for multiple observations by each patient. Setting: This is a national Canadian patient portal. Participants: A total of 2,431 patients participated. Main Outcome Measures: Self-ratings of efficacy of cannabis, defined as a three-point reduction in neuropathic pain, anorexia, anxiety symptoms, depressive symptoms, insomnia, and post-traumatic flashbacks. Results: We included 26,150 observations between October 1, 2017 and November 28, 2018. Of the six symptoms, response was associated with increased THC:CBD ratio for neuropathic pain (odds ratio [OR]: 3.58; 95% CI: 1.32-9.68; p = 0.012), insomnia (OR: 2.93; 95% CI: 1.75-4.91; p < 0.001), and depressive symptoms (OR: 1.63; 95% CI: 1.07-2.49; p = 0.022). Increased THC:CBD ratio was not associated with a greater response of post-traumatic stress disorder (PTSD)-related flashbacks (OR: 1.43; 95% CI: 0.60-3.41; p = 0.415) or anorexia (OR: 1.61; 95% CI: 0.70-3.73; p = 0.265). The response for anxiety symptoms was not significant (OR: 1.13; 95% CI: 0.77-1.64; p = 0.53), but showed an inverted U-shaped curve, with maximal benefit at a 1:1 ratio (50% THC). Conclusions: These preliminary results offer a unique view of real-world medical cannabis use and identify several areas for future research.
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