Scant evidence exists on the efficacy of medicinal cannabis in the TGA’s most-used approval category, Australian researchers say.

The TGA issued 112,000 approvals under Special Access Scheme Category B last year for ‘category 5’ products — those where cannabidiol comprises <2% of cannabinoid content, the rest typically tetrahydrocannabinol (THC).

But a TGA-commissioned study, published in Drug and Alcohol Review this month, found only six randomised controlled trials and nine observational studies on the medicinal cannabis products captured by category 5.

Only four studies were high quality, the researchers said, while the strongest THC concentration in the studies — 22% of total product weight — was weaker than what some Australian doctors were prescribing.