The researchers thus observed no particular benefit for several conditions for which the use of cannabis for medical purposes could be justified, such as anxiety disorders, psychotic disorders, anorexia, post-traumatic stress syndrome or even opioid use disorder.
“For several of the conditions for which cannabis is often used currently, the scientific data from this type of study indicates that we are not capable of detecting a therapeutic effect,” summarized Doctor Didier Jutras-Aswad, a specialist in the effects of cannabis in humans, particularly in terms of mental health, at the University of Montreal Hospital Center.
That being said, he adds, “this does not prevent a given person from being able to see a benefit from the use of a substance like cannabis in their very specific context. So, I also think we have to be careful.”
“We cannot deny the fact that people can have subjective experiences with a substance like cannabis, which can provide them, in this given context, with certain benefits,” said Dr. Jutras-Aswad.
Not surprisingly, the meta-analysis found that the use of medical cannabis could help reduce the intensity of withdrawal for patients who wish to reduce their consumption of the substance.
The researchers report a “decrease in autistic traits in people with autism spectrum disorder,” but emphasize that “the level of certainty of the data regarding this reduction in autistic traits was very low, and the two studies that provided data on this outcome were at high risk of bias.”
They also observed a reduction in insomnia symptoms and some data indicated an improvement in sleep duration. This was also the “only beneficial effect of cannabinoids for which the level of certainty was moderate”, according to measurements carried out using a device, they write.
Finally, cannabinoids appeared to reduce the severity of tics in patients with Tourette syndrome, but only if they received a combination of cannabidiol and THC.
Severe lack of data
The authors of the meta-analysis looked at 54 studies carried out between 1980 and 2025, which included a total of just under 2,500 participants. These studies evaluated cannabinoids as first-line treatment for mental or substance use disorders.
The authors found no double-blind randomized trials ― the gold standard for scientific research ― on the issue, highlighting a gaping gap in evidence.
“We barely have around sixty studies to get our teeth into,” lamented Doctor Jutras-Aswad. Despite the fact that it is widely used, despite the fact that many people report positive effects of this substance, despite the fact that we talk a lot about cannabis in our therapeutic arsenal, the level of evidence, the quality of evidence, the number of studies, is extremely limited.
One of the main findings of all this, he adds, “is that despite all the hubbub around cannabis, then the fact that we talk about it a lot, then that it is widely used rightly or wrongly, the data, the science is not there”.
“Science is not yet following the parade,” said Doctor Jutras-Aswad, who heads the department of psychiatry at the CHUM.
The authors of the study agree, noting that “the lack of evidence regarding the effectiveness of these treatments contrasts with the dramatic increase in their use in some regions, suggesting that regulatory oversight of the use of cannabinoids for medical purposes should be strengthened.”
“We regularly see that healthcare professionals feel ill-prepared when they have to tackle these treatments,” they point out.
“We probably have people who could benefit from cannabis for certain indications for therapeutic purposes and who do not have access to it because the medical profession is not yet fully trained or adequately trained,” confirmed Doctor Jutras-Aswad.
In addition, the Australian researchers continue, “it may be necessary to rethink public health messages regarding these drugs to minimize the negative or positive attitudes traditionally associated with non-medical use, both of which can lead to expectancy or placebo effects.”
They note that many people often report self-treating their health problems using non-medical cannabis products.
“Cannabis is one of the most widely used substances, so there are plenty of subjective or self-reports of people using cannabis for different reasons, with benefits or sometimes harm to themselves,” said Dr. Jutras-Aswad.
The study shows, however, its authors recall, that “only a small portion of cannabis-based products and dosage forms have been evaluated for their effectiveness and safety.”
“Messages aimed at the general public regarding cannabinoids for medical use should (therefore) emphasize the importance of the products tested,” conclude the Australian researchers.
The findings of this meta-analysis were published by the medical journal Lancet Psychiatry.
