Doctors are commonly prescribing high-dose medicinal cannabis containing up to four times the concentration of THC tested in clinical trials, a review has found.
Researchers from Monash University evaluated the available evidence for the efficacy and safety of higher THC potency medicinal cannabis products, in line with those being prescribed in Australia. THC, or delta-9-tetrahydrocannabinol, is the main psychoactive ingredient of cannabis.
There is no upper limit for THC concentration allowed in medicinal cannabis products in Australia, with higher-dose products such as dried herb and concentrated extract, known as Category 5 products, ranging from 13% to 88% THC.
Of more than 1,000 medicinal cannabis products available, only two have undergone pre-market evaluation by drugs regulator the Therapeutic Goods Administration (TGA) for quality, safety and efficacy.
A co-author of the review, Prof Suzanne Nielsen from the Monash Addiction Research Centre, said she and her colleagues reviewed studies that assessed how effective medicinal cannabis is for a range of conditions, but found only products containing up to 22% THC had been tested.
“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” she said.
The findings were published in the journal Drug and Alcohol Review.
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Nielsen said the TGA should consider setting THC concentration limits at or below the levels naturally occurring in the cannabis plant, at about 35%, “or even at 22% in line with what has been tested in trials”. Health warnings and better labelling of the products should also be considered, she said, along with improved screening and monitoring of harms.
“It’s also not clear how well consumers understand the products that they are using,” she said.
According to TGA data, chronic pain and anxiety drive the majority of prescriptions, with Category 5 products making up half of all approvals.
This is despite research that has found medicinal cannabis is no more effective than placebo at reducing anxiety symptoms, Dr Jack Wilson, with the University of Sydney’s Matilda Centre for Research in Mental Health and Substance Use, said.
“As for chronic pain, a 2018 review concluded that there was low quality evidence that cannabis may be associated with small reductions in pain,” Wilson said. “Further research is needed, particularly studies that include real-world doses and products.”
Nielsen said, historically, prescribed medicinal cannabis tended to be in the form of oral oils, but in recent years approvals had dramatically pivoted toward high-THC smoked or vaporised dried flower.
This “doesn’t really match where the evidence is for what works,” she said. “And actually, there’s very limited evidence in general for medicinal cannabis, but particularly for these high-concentration THC products and inhaled forms.”
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A spokesperson for the TGA told Guardian Australia that 27 cases involving medicinal cannabis had been voluntarily reported to its adverse events database so far in 2026, though a report is not proof that the product caused the adverse symptoms.
An analysis of 614 medicinal cannabis adverse event reports to the TGA between mid-2022 and mid-2025 found that half were related to Category 5 products. They included acute harms such as psychosis, cannabis hyperemesis syndrome (cycles of nausea, vomiting and abdominal pain after long-term use), and suicidal behaviour.
Wilson said he is concerned the products might delay or replace the use of evidence-based treatments. “The regular consumption of THC is also associated with a greater risk of short- and long-term harms, possibly making the patient’s condition even worse,” he said.
A 2025 review of cannabis prescribing by the Australian Health Practitioner Regulation Agency (Ahpra) found concerns from medical regulators that “profits are being prioritised over patient safety in some medicinal cannabis prescribing practices”.
The Ahpra review identified some practitioners who had individually issued more than 10,000 prescriptions for high-strength THC medicinal cannabis products in six months, and highlighted cases of consultations lasting just a few seconds.
Wilson said with the rise of telehealth clinics and direct-to-consumer marketing, “suppliers are clearly prioritising profit over the health of patients”.
Guardian Australia has contacted the Royal Australian College of General Practitioners for comment.
