Alongside chronic pain, mental health conditions are among the most common reasons people turn to marijuana for medical use. However, a comprehensive review of cannabis research spanning the past 45 years finds little to no high-quality data supporting its effectiveness for these medical conditions.
Published in the Lancet journal, the meta-analysis found cannabinoids (a type of medicinal cannabis) had no meaningful benefit or significant impact on primary outcomes for anxiety, PTSD, psychotic disorders (including schizophrenia), anorexia nervosa, OCD, opioid use disorder, cocaine use disorder, bipolar disorder, ADHD, and tobacco use disorder. To date, this is the largest and most comprehensive systematic review and meta-analysis of data from randomised control trials (RCTs) on the effectiveness and safety of cannabinoids for the treatment of mental disorders and SUDs. The team of researchers in Australia reviewed 54 trials involving 2,477 participants, considering a wide range of conditions, formulations and types of cannabinoids.
The study found that the use of medicinal cannabis for common psychiatric conditions like anxiety, PTSD, and depression was ineffective. Interestingly, they found it did have some impact (though small and the evidence was deemed low-quality by the study’s authors) on conditions like insomnia, autism and tic or Tourette’s syndrome. One of the study’s authors, Jack Wilson, a postdoctoral research fellow at the Matilda Centre for Research in Mental Health and Substance Use at the University of Sydney, says, “We clearly need to do more research on cannabis medicines.” “In the absence of evidence at this time, the routine use of medical cannabis products really should be rarely justified for the treatment of mental health disorders,” he told NPR.
He isn’t the only cannabis researcher echoing these sentiments. Ryan Vandrey, a professor of psychiatry and behavioural sciences at Johns Hopkins University School of Medicine who studies cannabis, says, “It’s embarrassing how little we have done in terms of data collection, given how widely this is available as a therapeutic”. Regarding the study, he says, “Though done well, a review of this nature invariably comes with major limitations. It collapses data across different products, doses, routes of administration, patient populations, and so on — and excludes findings from long-term observational studies and other sources of evidence. “So it can be challenging to draw firm conclusions, especially when there are not that many actual studies or patients being evaluated,” he says.
This study closely follows another substantial review, published earlier this month in JAMA Internal Medicine. That study adopted a broader methodological approach — including observational research and other study designs beyond randomised controlled trials — yet reached a similar conclusion: there is little convincing evidence that cannabinoids substantially treat mental health conditions. It also issued a caution regarding vulnerable populations, highlighting particular concerns for adolescents, young adults, individuals at risk of substance use disorders, and those living with bipolar disorder or psychotic conditions. This is not a new warning — the association between early cannabis use and increased risk of psychosis is among the more well-established findings in the field.
Whilst the research has technical limitations, like most research studies, its findings can’t be overlooked nor understated. The fact remains that in many countries where medicinal cannabis is loosely regulated, and its advocates are calling for even laxer controls (including NZ) due to the supposed benefits, the science states otherwise.
As the study’s authors noted, due to limited evidence of effectiveness and a higher risk of all-cause adverse outcomes, the routine use of these medicines for mental disorders and SUDs is rarely justified. It is time for laws, policies, and even politicians to keep pace with the science.
*Written by Family First staff writers*
