The number of Australians using medicinal cannabis has increased over the past five years. About 700,000 Australians have used cannabis for their health in the past year.
And from 2022, sales of medicinal cannabis have increased fourfold. But the majority of prescription products on the Australian market are not registered in the Management of Therapeutic Products. This means they have not been rigorously tested.
So, is medicinal cannabis safe? And is it really effective?
Us new researchpublished today in Lancet Psychiatry, is the largest review ever to examine the safety and effectiveness of medicinal cannabis for mental health and substance use disorders.
These make up six of the first ten reasons Cannabis is specifically prescribed for: anxiety, sleep disorders, post-traumatic stress disorder (PTSD), insomnia, depression and attention deficit hyperactivity disorder (ADHD).
But we found little evidence that medicinal cannabis effectively treats these conditions. And while most side effects were mild to moderate, some serious safety questions remain.
What evidence was available?
Between 1980 and 2025, we found 54 randomized controlled trials that examined whether medicinal cannabis reduced or treated mental health disorders (including psychotic disorders, anxiety, insomnia, anorexia and PTSD) or substance use disorders (including cannabis and the opioid, cocaine). This type of testing is the gold standard for understanding the immediate effects of a drug.
The most common cannabinoid evaluated was cannabidiol (CBD), followed by tetrahydrocannabinol (THC) and a combination of THC and CBD.
CBD is non-intoxicating and usually safewhile THC is psychoactive, and is associated with impairments in the short term, such as paranoia, and in the long term, such as the development of a cannabis use disorder.
Cannabis can help people quit cannabis
We found that cannabis medicines were no more effective than a placebo in treating symptoms of psychotic disorders (such as schizophrenia), anxiety, PTSD, anorexia or opioid use disorder.
However, there have been promising findings that medicinal cannabis may be effective in reducing cannabis use among people with cannabis use disorder.
While this may sound strange, the drugs largely consisted of an oil-based combination of CBD and THC that was taken orally. As these drugs reduce cravings, patients may use less cannabis than they usually do. So, for people who regularly smoke high-THC cannabis, using medicinal cannabis can reduce their risk for related health problems, such as lung disease.
But there are limitations
We must be cautious when interpreting the positive findings.
For example, some evidence suggests that medicinal cannabis could help treat symptoms associated with tic or Tourette syndrome, insomnia and autism spectrum disorder. But only a small number of studies focused on these conditions, and many were of low quality.
In randomized controlled trials, we don’t want participants to know whether they consume the drug or the placebo. But as cannabis is often intoxicating, participants may not know what they have been given and this may introduce bias.
Some of these studies also reported conflicts of interest, which may have influenced their results. Therefore, it may be too early to tell whether medicinal cannabis is effective in treating these conditions.
How about security?
The combined data showed that cannabis medicines were associated with mild side effects such as nausea, dry mouth and fatigue.
But the risk of serious side effects, such as a psychotic episode, was not greater among those taking cannabis medicine or placebo.
The data alone seems to suggest that cannabis medicines are relatively safe. But this may not be reflected in actual usage.
The average duration of treatment in these studies was only five weeks – and we know that regular cannabis use can cause long-term damage.
A review of 2024 I establish about a quarter of those who use medicinal cannabis will develop a cannabis use disorder. This is it similar in the percentage among those who use cannabis for non-medical purposes.
The cannabis medicines used in these studies were also low in THC. However, data from the TGA shows that Australians have access to a wide range of cannabis medicines often high in THC. Chronic use of high THC cannabis has been connected at greater risk of worsening mental health symptoms, particularly among young people.
So what does this mean?
Similar reviews have been conducted sometime. But many focus on a smaller number of health conditions and have not combined data to reveal a single estimate.
Reviews have also typically drawn conclusions about cannabis as a mental health treatment when it was used to treat other conditions, such as chronic pain.
However, our findings are largely consistent with previous reviews: there is little evidence that medicinal cannabis is an effective treatment for mental health and substance use disorders.
Currently, there is a mismatch between research evidence on medicinal cannabis – mostly short-term trials and CBD formulations – and actual use, which is longer term and often uses high-THC products.
We need more research into cannabis medicines, particularly for conditions with limited alternative treatments, and follow-up over longer periods.
As conducted by the TGA a review of the prescription of medical cannabis in Australiathese findings should inform future regulations. Long-term use of these drugs could lead to harm and delay the use of more effective treatments.
The takeaway
For those who believe their medicinal cannabis is beneficial for these conditions, our review is not meant to contradict your experience.
However, we encourage you to regularly discuss your situation with a doctor and, if possible, consider evidence-based alternative treatments.
