Millions Use Cannabis for Mental Health. The Science Tells a Different Story.

Medical cannabis and mental health have become closely linked in public conversation, but the science has not kept pace. For years, people have turned to cannabis to manage anxiety, depression and post-traumatic stress disorder (PTSD). In some parts of the United States, doctors can formally authorise it for these conditions. Two major new studies now show that this widespread belief in its effectiveness runs far ahead of actual evidence.

The Lancet Psychiatry published a landmark review finding no reliable evidence that cannabis helps treat anxiety, PTSD or depression. The Journal of the American Medical Association (JAMA) published a separate review reaching almost identical conclusions. Both research teams warned that real-world use and clinical evidence sit on very different ground.

What the Research Found About Cannabis for Mental Health Conditions

Scientists behind the Lancet Psychiatry study analysed 54 randomised controlled trials. The research covered studies published between 1980 and 2025. These trials are the gold standard for evaluating new medicines. The findings were stark. Cannabis showed no measurable effect for anxiety disorders, PTSD, anorexia nervosa or psychotic disorders. Not a single randomised controlled trial had tested cannabis as a treatment for depression.

“For a long time, people have been using cannabis to cope with mental illness,” said Tory Spindle, a psychologist at Johns Hopkins University School of Medicine. “What is really lacking is controlled, rigorous evidence, which would be the same standards you would want for any medication.”

The JAMA review echoed those concerns and went further. Psychiatrist Deepak Cyril D’Souza of Yale University led the review. His team found that cannabis for mental health conditions can actively cause harm. Cannabis worsened manic symptoms in people with bipolar disorder. It also worsened psychotic symptoms in people with conditions such as schizophrenia.

“Both of us reached the same conclusion,” D’Souza said. “There is very little, and mostly low-quality, evidence to support any efficacy of cannabis derivatives in the treatment of mental health disorders.”

How Medical Cannabis and Mental Health Policy Got Ahead of Science

The problem partly stems from how medical cannabis has been legalised in the United States. In most countries, a new drug must complete at least one randomised controlled trial before authorities approve it. Medical cannabis skipped that process entirely.

Cannabis remains a Schedule I controlled substance at the federal level. The government classifies it as having high abuse potential and no accepted medicinal use. That classification creates significant barriers for researchers who want to study it properly. Individual states have legalised medical cannabis and set their own qualifying conditions, without waiting for clinical evidence.

Today, 40 US states and Washington DC permit medical cannabis. More than a dozen states list PTSD as a qualifying condition. A handful explicitly include anxiety and depression. Others allow them under broad categories such as “debilitating psychiatric conditions.”

“The way cannabis for medical use has been rolled out is completely backwards from how medications are typically brought to market,” Spindle said.

Jack Wilson of the University of Sydney, who led the Lancet study, was equally direct. “We all just want people to be able to access medicines that are both effective and safe for their conditions. Unfortunately, for a lot of people using medical cannabis, I don’t think that is the case.”

Why This Matters Beyond the United States

These findings carry weight far beyond American borders. Debates over cannabis legalisation are active across the world. The assumption that medical cannabis and mental health treatment naturally go together deserves serious scrutiny.

Most of the 54 trials reviewed involved fewer than 100 participants. That limits what conclusions researchers can draw. But the absence of positive evidence across more than four decades of research is a signal policymakers and patients cannot ignore.

Cannabis also complicates the picture because it is not one single substance. Different strains, doses and delivery methods produce very different effects. Most trials have not examined these variables in enough detail to produce actionable guidance on cannabis for mental health conditions.

The Takeaway

The evidence is clear. Using cannabis to manage mental health conditions has no scientific backing, and for many people it carries real risks. Anecdotal relief is not the same as a safe or effective treatment. Turning to an unproven substance can delay access to care that actually works.

“What’s happening in the real world and the medical evidence, there’s a big gap between the two,” D’Souza said.

That gap has consequences. People who turn to cannabis instead of proven mental health support may find their symptoms getting worse, not better. This is especially true for those living with bipolar disorder, schizophrenia, or other serious psychiatric conditions. Medical cannabis and mental health recovery are simply not the straightforward pairing many people assume. Anyone struggling with anxiety, depression or PTSD deserves access to treatments that have been properly tested and shown to genuinely help.

Source: scientificamerican