Medical cannabis eases chronic pain only slightly, and dizziness comes with it

Chronic pain is one of the most common reasons people seek treatment, and medical cannabis is increasingly offered as an option for it. Yet patients and clinicians have lacked a clear, honest accounting of what cannabis actually delivers: how much pain relief, whether daily functioning and sleep improve, and what side effects come along for the ride. This review set out to answer exactly that question by gathering every randomised trial of medical cannabis or cannabinoids for chronic pain, covering both cancer related and non-cancer pain, and weighing benefits against harms in one place.

The researchers swept eleven databases and trial registries up to January 2021 for randomised trials comparing medical cannabis or cannabinoids against any non-cannabis control, with at least one month of follow-up. They found 32 trials covering 5174 adult patients, 29 of which used a placebo comparison. The cannabis was taken orally in 30 trials and applied topically in 2; none of the included trials studied inhaled cannabis. Most trials (28) involved chronic non-cancer pain and 4 involved cancer related pain, with follow-up ranging from 1 to 5.5 months. Paired reviewers independently assessed each trial for bias, and the certainty of every finding was formally graded.

Compared with placebo, non-inhaled medical cannabis probably produces a small increase in pain relief: about 10% more patients achieved at least the minimally important 1 cm improvement on a 10 cm pain scale. Oral cannabis also delivered a very small improvement in physical functioning (a 4% difference in patients reaching a meaningful gain, high certainty) and a small improvement in sleep quality (a 6% difference, high certainty). It did not improve emotional, role or social functioning. On the harms side, it raised the risk of transient cognitive impairment by 2%, vomiting by 3%, drowsiness by 5%, impaired attention by 3% and nausea by 5%, but not diarrhoea. Dizziness rose by 9% in trials under 3 months and by 28% in trials of 3 months or longer.

This is one of the most comprehensive syntheses of randomised cannabis trials for chronic pain, and the moderate to high certainty of its main findings puts it well above the usual back-and-forth of single studies. It confirms that cannabis is not inert for pain, but it also sizes the benefit as small to very small, which complicates the more enthusiastic claims made for medical cannabis. The findings fed directly into an accompanying BMJ Rapid Recommendation. Open questions remain: inhaled cannabis was not covered, follow-up stopped at 5.5 months, and the sharp rise in dizziness over longer use deserves further study.

If you live with chronic pain and have wondered whether medical cannabis is worth exploring, this gives you a realistic picture rather than a marketing one. The honest summary is that non-inhaled cannabis helps some people a little: a modest gain in pain relief, a small lift in sleep quality and a very small one in physical functioning, with mood and social life unchanged. Against that sit genuinely common side effects, particularly dizziness and drowsiness, which grew more likely the longer people used it. This is a reason to go in with expectations set at small benefit and real trade-offs, and to discuss both sides with whoever manages your pain.