A review by Monash University researchers has found that doctors in Australia are frequently prescribing high-dose medicinal cannabis containing up to four times the concentration of THC tested in clinical trials. THC (delta-9-tetrahydrocannabinol) is the main psychoactive ingredient in cannabis.
There is no upper limit for THC concentration in Australian medicinal cannabis products. Higher-dose products—known as category 5 products, including dried herb and concentrated extract—range from 13% to 88% THC. Of more than 1,000 available medicinal cannabis products, only two have undergone pre-market evaluation by the Therapeutic Goods Administration (TGA) for quality, safety, and efficacy.
Evidence mismatch
Professor Suzanne Nielsen, co-author of the review from the Monash Addiction Research Centre, said the research team examined studies assessing medicinal cannabis effectiveness for various conditions. They found that only products containing up to 22% THC had been tested in randomised controlled trials. “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.
Calls for regulation
Nielsen said the TGA should consider setting THC concentration limits at or below levels naturally occurring in the cannabis plant—about 35%—or even at 22% in line with trial-tested products. She also recommended health warnings, better labelling, and improved screening and monitoring of harms. “It’s also not clear how well consumers understand the products that they are using,” she added.
According to TGA data, chronic pain and anxiety drive most prescriptions, with category 5 products making up half of all approvals. However, research has found medicinal cannabis is no more effective than placebo for reducing anxiety symptoms, according to Dr Jack Wilson from the University of Sydney’s Matilda Centre for Research in Mental Health and Substance Use. “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.”
Shift to high-THC inhaled forms
Nielsen noted that prescriptions historically tended to be oral oils, but approvals have 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.”
Adverse events and profit concerns
A TGA spokesperson told Guardian Australia that 27 cases involving medicinal cannabis had been voluntarily reported to its adverse events database so far in 2026 (note: as per source), though a report is not proof that the product caused the symptoms. An analysis of 614 adverse event reports between mid-2022 and mid-2025 found half were related to category 5 products, including acute harms such as psychosis, cannabis hyperemesis syndrome, and suicidal behaviour.
Wilson expressed concern that the products might delay or replace 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 review identified practitioners who had individually issued more than 10,000 prescriptions for high-strength THC products in six months and highlighted cases of consultations lasting just seconds.
Wilson said with the rise of telehealth clinics and direct-to-consumer marketing, “suppliers are clearly prioritising profit over the health of patients.”
The president of the Royal Australian College of General Practitioners, Dr Michael Wright, supported these concerns. “Profits can’t be prioritised over patient safety,” he said. “Online cannabis clinics operating as businesses create conflicts of interest, fragment care and put patients at risk.” Wright called for a review of medicinal cannabis product categories and noted an increase in psychosis presentations at hospitals after use. “There’s no clinical need for THC concentrations to be this high,” he said. “For issues such as chronic pain and insomnia there are effective, evidence-based therapies already available.”
