Withdrawal because of an adverse event was more frequent in the cannabinoid arm of the capsule trial, but the comparative estimate was imprecise. The reasons for withdrawal also differed between groups.
The counts and reasons both mattered
The 2018 review reported adverse-event withdrawals in ten of 29 cannabinoid participants and five of 31 placebo participants. The risk ratio was 2.14, with a 95% confidence interval of 0.83 to 5.51. The review characterized the evidence as low certainty.
Withdrawals in the cannabinoid group were mostly attributed to dizziness; placebo withdrawals were attributed to worsening ulcerative colitis. Both appear under the same endpoint label while describing different clinical experiences.
Retention is not one uniform biological outcome
Combining withdrawals into a total is useful for comparing treatment continuation. It does not make dizziness and disease worsening the same event or establish that either mechanism explains every discontinuation. Reasons should remain visible alongside the aggregate result.
Avoid opposite overstatements
The point estimate should not be announced as a precisely established doubling of risk, because the interval included one and was wide. Conversely, statistical uncertainty does not erase the observed tolerability problem. These short-term human data support reporting both the events and their uncertainty, not a claim of universal safety or a prediction of how one patient will respond.
Related reading: why endpoint definitions matter.
Research cited
Kafil and colleagues (2018). Cannabis for the treatment of ulcerative colitis. DOI: 10.1002/14651858.CD012954.pub2.
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