Cannabinoids cannot be recommended for chronic pain in adult patients with advanced cancer as they are no more effective than placebo, UK researchers say.

Their systematic review and meta-analysis showed no difference in pain scores between clinically relevant cannabinoids and placebo. But it did find a higher risk of adverse events with the active agents.

Six randomised controlled trials, including phase 2 and 3 studies, were included in the review. The meta-analysis included five trials with 1442 patients taking tetrahydrocannabinol: cannabidiol or nabiximols adjunctive to an existing stable dose of opioids or placebo.

In phase 3 studies, the patients titrated medication, delivered via pump-action oromucosal spray, until they either achieved pain relief, developed adverse events or reached the maximum dose of 10 sprays a day.