A Cannabis-Spray Brachial-Plexus Trial Met Statistical but Not Its Assumed Clinical Threshold

A brachial-plexus-avulsion pain trial found a statistically significant advantage for THC:CBD spray but did not meet the prespecified level assumed for clinical significance. Those are separate judgments about the same pain comparison.

The review reports a small between-group difference

The study involved central neuropathic pain after brachial plexus avulsion, an injury affecting nerves serving the upper limb. The review’s table lists 48 randomized participants, with 45 completing the trial. It reports a difference of approximately 0.58 points versus placebo on a 0–10 pain measure during the assessed period, with p = 0.005.

Statistical evidence does not determine useful magnitude

A p-value concerns compatibility with a statistical null under the analysis assumptions. It does not state how large or useful a benefit is to patients. The review specifically notes that the pain difference failed to satisfy the study’s a priori assumed level for clinical significance. Both observations belong in the result: evidence of a difference, and a difference smaller than the trial’s assumed clinical target.

Keep the threshold in its proper role

Failure to reach that assumed magnitude does not prove that no participant valued any relief. Equally, a favorable p-value does not establish a broadly important average benefit or justify describing the treatment as highly effective. The finding concerns a defined THC:CBD oromucosal spray, a specific nerve-injury population and a short trial. It cannot be transferred automatically to other neuropathies or cannabis preparations. A treatment-evidence appraisal should report the scale, between-group magnitude and clinical threshold together, rather than letting statistical significance stand in for the size of the effect.

Related analysis: the broader findings and limitations of this research.

Research cited

The study observations discussed here are reported in the supplied review: Überall (2020). A Review of Scientific Evidence for THC:CBD Oromucosal Spray (Nabiximols) in the Management of Chronic Pain. Journal of Pain Research.