Despite the hype around cannabis products, there is “very little scientifically valid research into most of these products” according to a new systematic review by researchers at Oregon Health & Science University. Reviewers searched more than 3,000 studies in the scientific literature and found only 25 with scientifically valid evidence—18 randomised controlled studies and seven observational studies of at least four weeks. A review of these 25 studies concluded there was “insufficient evidence for the long-term pain-relieving effect of cannabis”. This is consistent with a 2020 review by psychiatrists at the University of Melbourne, which concluded “the evidence is too weak’ to prove cannabis helps anxiety, depression or insomnia”.
“Many reviews were unable to provide firm conclusions on the effectiveness of medical cannabis, and results of reviews were mixed. Mild adverse effects were frequently but inconsistently reported, and it is possible that harms may outweigh benefits.”
“In general, the limited amount of evidence surprised all of us,” said lead author Marian S. McDonagh, Pharm.D., emeritus professor of medical informatics and clinical epidemiology in the OHSU School of Medicine.
“Unfortunately, there is very little scientifically valid research into most these products,” she said. “We saw only a small group of observational cohort studies on cannabis products that would be easily available in states that allow it, and these were not designed to answer the important questions on treating chronic pain.”
Researchers found many of the products now available at U.S. dispensaries have not been well studied.
“For some cannabis products, such as whole-plant products, the data are sparse with imprecise estimates of effect and studies had methodological limitations,” the authors write.
This situation makes it very difficult to for health professionals to safely guide patients.
Pro-cannabis advocates greatly overstate the supposed ‘health’ benefits of cannabis, yet there is simply very little evidence for the benefits of the drug. There are major gaps in knowledge that put in doubt the efficacy and safety of medical cannabis.
Before any drug is approved and released to the wider population, it must typically undergo a lengthy review process involving extensive research and ongoing clinical trials. This simply has not been done for most cannabis products. In fact, since cannabis products vary significantly in chemical make-up, it means no two cannabis products are the same.
“Cannabis products vary quite a bit in terms of their chemical composition, and this could have important effects in terms of benefits and harm to patients,” said co-author Roger Chou, M.D., director of OHSU’s Pacific Northwest Evidence-based Practice Center. “That makes it tough for patients and clinicians since the evidence for one cannabis-based product may not be the same for another.”
Yes, researchers did find some evidence to support a short-term benefit in treating some neuropathic pain caused by damage to peripheral nerves. This research involved only two cannabis products. Both products also lead to notable side effects including sedation and dizziness, according to the review.
The harms of medical cannabis may outweigh any claimed benefits.