Updated Cochrane review finds moderate evidence for cannabis in chronic pain, but significant gaps remain

An updated Cochrane systematic review — widely considered the gold standard for evidence-based medicine — has concluded that there is moderate-quality evidence that cannabis-based medicines can reduce chronic pain, though the effect size is modest and must be weighed against a significant rate of side effects.

What the review found

The review analyzed 50 randomized controlled trials involving more than 9,000 participants with chronic non-cancer pain conditions. The key findings:

• Participants using cannabis-based medicines were 30% more likely to report a meaningful reduction in pain compared to placebo
• The average pain reduction was approximately 1 point on a 10-point scale — statistically significant but clinically modest
• Number needed to treat (NNT): approximately 6 patients need to be treated for one to achieve substantial pain relief beyond placebo
• Products containing both THC and CBD showed stronger effects than CBD-only preparations
• Inhaled and oral formulations showed similar efficacy

Adverse events

The review documented a significantly higher rate of adverse events in the cannabis groups:

• Dizziness was the most commonly reported side effect (reported by approximately 25% of participants)
• Drowsiness, dry mouth, and nausea were also frequently reported
• Cognitive effects including difficulty concentrating were noted in THC-containing products
• Serious adverse events were rare but occurred at a slightly higher rate than placebo

The number needed to harm (NNH) was approximately 4 — meaning for every four patients treated, one would experience an adverse event they would not have experienced on placebo. This NNH being lower than the NNT (6) is a notable finding.

What this means

The Cochrane review lands in a nuanced middle ground. Cannabis is not the miracle pain treatment that some advocates claim, but neither is it the pharmacologically empty substance that skeptics suggest.

The evidence is strongest for neuropathic pain — pain caused by nerve damage or dysfunction. Conditions like diabetic neuropathy, post-surgical nerve pain, and multiple sclerosis-related pain showed the most consistent response to cannabis-based medicines.

The evidence is weaker for musculoskeletal pain (arthritis, back pain) and fibromyalgia, conditions for which many patients currently use cannabis.

Context matters

The reviewers emphasized several important contextual points:

• Most studies were short-term (4-12 weeks). Long-term safety and efficacy data remains scarce.
• Dosing varied enormously across studies, making it difficult to establish optimal protocols
• Many studies were industry-funded, which the reviewers flagged as a potential source of bias
• The placebo response in chronic pain trials is historically high, complicating interpretation

Clinical implications

For physicians considering cannabis-based treatments for chronic pain patients, the review suggests a cautious, individualized approach: cannabis-based medicines may be reasonable as a second or third-line option for neuropathic pain in patients who have not responded to conventional treatments, provided the patient is monitored for adverse effects.

For the broader policy conversation, the review adds another data point to the slow accumulation of clinical evidence about what cannabinoids can and cannot do.