The scant evidence for cannabis to treat mental health conditions highlights a research gap

Along with chronic pain, mental health conditions are some of the top reasons people use marijuana for medical purposes.

But an extensive review of cannabis studies over the past 45 years has concluded that there is no high-quality evidence that it is effective.

The findings, published in the Medical Journal Lancet Psychiatry The extent to which the general public’s consumption of cannabis hinders scientific research.

The new analysis represents the largest attempt to systematically analyze all data from randomized controlled trials on cannabis and mental health. A group of researchers in Australia reviewed more than 50 clinical trials, looking at many conditions, formulations and types of cannabinoids.

The analysis found no evidence that cannabis can help with symptoms of anxiety, post-traumatic stress disorder or depression — the psychological conditions that medical marijuana users often cite when asked why they take the drug.

Insomnia, autism and tic or Tourette syndrome had more supportive data, although the evidence was considered “low quality” by the authors.

“We clearly need a lot more research on cannabis,” says Jack Wilson, a postdoctoral research fellow at the Matilda Center for Mental Health and Substance Use at the University of Sydney, who led the review. “In the absence of evidence at this time, the routine use of medical cannabis products should rarely be justified for the treatment of mental health disorders,” he told NPR.

The findings aren’t entirely surprising to cannabis researchers who know firsthand how challenging it can be to conduct and fund well-controlled trials. For more than 50 years, marijuana has been listed as a Schedule 1 drug by the Drug Enforcement Administration, although President Trump recently indicated that he wants the federal government to loosen that designation.

Even as many states have moved to legalize medical and recreational marijuana, this has not resulted in large investments in high-quality studies that medicine relies on when evaluating treatments.

Because d Lancet Psychiatry The paper had strict criteria for which studies could be considered, and the final analysis included data from only about 2,500 patients. And for some conditions, such as depression, there is no single trial.

“It’s a shame how little we’ve done in terms of data collection, given that it’s so widely available as a treatment,” says Ryan Windry, a professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine who studies cannabis.

Although well done, a review of this nature always comes with major limitations, he says. It excludes data from different products, doses, routes of administration, patient populations, etc. – and excludes findings from long-term, observational studies and other sources of evidence.

“So it can be challenging to draw firm conclusions, especially when many real studies or patients are not evaluated,” he says.

Lancet Psychiatry The study comes on the heels of another major review published earlier this month JAMA Internal Medicine.

It took a broader view—considering other types of studies, not just controlled trials—but reached similar conclusions about the lack of evidence for treating mental health conditions.

It also warns of “significant risks” in vulnerable groups, including teenagers and young adults, those at risk of substance use disorders, as well as people with bipolar disorder or psychotic disorders. There is a well-documented link between cannabis use at a young age and an increased risk of mental illness.

“What we wanted to do was show that marijuana is not one thing because it’s such a complex substance,” says Dr. Devan Kansagara, MD, professor of medicine at Oregon Health & Science University and the Portland VA.

Kinsgara, who runs a Department of Veterans Affairs-funded project to synthesize the evidence on cannabis, says doctors should talk to their patients who use marijuana, while acknowledging that there are still big gaps in our knowledge.

One take-home message from their work is the emphasis on dosage—that high-THC products such as gummies and concentrates, especially for those with serious mental illness, seem to carry the greatest risks.

Choosing a low-dose THC product is “a way to closely balance the benefits and harms,” ​​he adds.

Cannabis can have “a wide variety of physiological effects” depending on the compound, although some of its nuances are lost. Lancet Psychiatry study, says Ziva Cooper, a professor of psychiatry who directs the UCLA Center for Cannabis and Cannabinoids.

For example, he says the review indicates that “cannabinoids as a whole have not been shown to be beneficial for anxiety,” but the picture changes when you look at specific compounds in the plant, such as cannabidiol, or CBD, that have shown promise.

“We have to be open to integrating other types of data that aren’t necessarily from placebo-controlled studies,” Cooper says.

Wandre has been involved in several research studies that have “shown significant clinical benefits to patients with anxiety and depression,” he says. Neither included Lancet Psychiatry analysis because they do not meet the criteria.

“There’s a subset of people with anxiety, depression or PTSD who can realize a lot of benefit when they start using a cannabis product for that purpose,” Wandre says. “Now we’re also seeing some patients try it and really have no effect. And some patients try it and get worse.”