Medicinal Cannabis THC Levels: Australians Prescribed High Doses 2026

Medicinal cannabis with very high THC levels is being regularly prescribed to Australians, with concentrations up to four times higher than those tested in clinical trials. A review by Monash University researchers found that while clinical evidence supports products containing up to 22% THC, many prescribed products range from 13% to 88% THC, raising serious safety concerns.

High THC Prescriptions: The Evidence Gap

The review, published in the Drug and Alcohol Review, evaluated randomized controlled trials (RCTs) for medicinal cannabis efficacy across various conditions. Researchers discovered that only products with up to 22% THC had been rigorously tested, yet Australian prescribers commonly offer category 5 products—dried herb and concentrated extracts—with THC levels reaching 88%.

Professor Suzanne Nielsen from the Monash Addiction Research Centre highlighted the mismatch: “When we looked at the randomised control trial evidence, which is the strongest evidence that we have to see if a product works for a particular condition, we saw there is a real mismatch between the evidence we have to draw on and the products being prescribed and used.”

Why THC Concentration Matters

THC (delta-9-tetrahydrocannabinol) is the primary psychoactive component of cannabis. Higher concentrations increase the risk of adverse effects, including anxiety, paranoia, cognitive impairment, and dependency. With no upper limit in Australia, patients may be exposed to unnecessary harms without proven added benefit.

TGA's Regulatory Gaps

Of more than 1,000 medicinal cannabis products available, only two have undergone pre-market evaluation by the Therapeutic Goods Administration (TGA) for quality, safety, and efficacy. This lack of oversight means most products are prescribed off-label without robust evidence.

Comparison: Clinical Trial THC vs. Prescribed THC

Recommendations for Safer Use

Professor Nielsen and her colleagues suggest the TGA should consider setting THC concentration limits at or below naturally occurring levels (about 35%), or even at 22% in line with trial evidence. They also call for improved health warnings, better labelling, and enhanced screening and monitoring of harms.

• Set maximum THC limits based on clinical evidence
• Mandate clear labelling of THC content
• Implement routine patient monitoring for adverse effects
• Increase pre-market evaluation of medicinal cannabis products

Key Takeaways for Patients and Prescribers

Patients using medicinal cannabis should ask their doctor about the THC concentration and whether it aligns with clinical trial evidence. Prescribers should consider starting with lower-THC products and titrating carefully, while monitoring for side effects.

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