Forty five percent of GPs have had at least one patient who has experienced a negative effect from medicinal cannabis in the last six months, according to a Healthed survey with 845 respondents so far.

Anxiety was the most common side effect attributed to medicinal cannabis, cited by 29% of GPs – but others included pain, cough, headaches, aggressive behaviour and more.

GPs also mentioned patients experiencing dry mouth, fatigue, vomiting, dizziness, confusion, demotivation and changes in appetite, as well as exacerbation of underlying mental health issues.

The results come after the TGA released data which showed 615 adverse events had been reported in the three years up to June 2025. These included 76 reports of anxiety, 65 reports of headache and more than 50 reports each for psychotic disorder, cough and nausea.

Somnolence (35 reports), paranoia (34 reports), hallucination (32 reports), pain (28 reports) and abdominal discomfort (27 reports) were also on the list, and were corroborated by GPs in Healthed’s survey. There were also 14 reports of suicidal ideation or behaviour to the TGA.

The data was released following a Freedom of Information request by the ABC, with the TGA noting that the adverse events do not prove causality, stating that the associations are suspected but “the symptom may be related to the underlying illness or to other factors,” and there may be no relationship, explaining that “it may be a coincidence that the adverse event occurred when the medicine was taken.”

Adverse events likely even more prevalent

Still, many are concerned.

The TGA itself has said that adverse events are likely under reported.

“Although adverse events associated with medicinal cannabis products are required to be reported to the TGA, it is highly likely that there is considerable under reporting due to the potential stigma associated with use, concerns over losing access, prescribers and patients not being clear on which adverse events may potentially be associated with medicinal cannabis product use, and a lack of effective regulatory controls,” the TGA’s consultation paper on safety and regulatory oversight of unapproved medicinal cannabis products explains.

Gold Coast based GP Dr Bryce Joynson, an experienced adult and paediatric cannabis prescriber and clinical educator on neurodiversity and endocannabinoid medicine, says that while cannabis is very safe compared with many other drugs, there are harms associated with it, including the risk of dependency and potential medication interactions. These are being exacerbated by unscrupulous business practices of some online clinics, he notes.

“Psychiatrists are worried about THC induced psychosis because patients are using large amounts of unregulated cannabis. And they might be combining it with benzodiazepines, opiates, amphetamines, antidepressant. And they’re adding it in with all of their other things without any proper medical oversight,” Dr Joynson says.

“Patients who are prescribed a high amount of THC dried herb can be at increased risk of developing side effects of therapy, as it can blunt the endocannabinoid receptors — and you may need escalating doses of THC to activate those receptors next time,” he says.

Dependency on THC can lead to worsening of the very symptoms cannabis was prescribed for, such as insomnia, chronic pain and mental health issues, he adds.

“More education around the benefits of CBD and minor cannabinoids such as CBG and CBN and responsible prescribing/use of THC is required, for patients and medical professionals,” he says.

How policy is playing a role

University of Sydney researchers Rose Cairns and Nicholas Buckley say there is some evidence that the loosening of restrictions around cannabis may be linked with increasing mental health concerns. For example, they note Canadian research that found schizophrenia associated with cannabis use increased by nearly three times after cannabis was legalised there, while ED presentations for anxiety also increased.

Their research published in the Medical Journal of Australia this year documented a rise in calls about cannabis poisoning.

“Best practice would involve new cannabis medicines being prescribed only by a person’s usual GP or specialist. This would typically require considerable time to advise on risks and benefits, and assess for drug interactions, or contraindications (where use is advised against), such as if someone has a history of psychiatric illness or substance use,” Cairns and Buckley write.

Dr Joynson points out that the dubious business models of many vertically integrated online clinics are putting vulnerable patients at particular risk.

“A huge proportion of these patients are suffering from mental health conditions or chronic pain. They are very vulnerable populations to begin with, and they actually need the most support and care from their practitioners,” he says.

However, it is certainly not going unnoticed. AHPRA is cracking down on inappropriate prescribing, and the TGA’s review of safety and regulatory oversight is currently open, with submissions due on 7 October.