In a systematic review of the scientific literature, researchers find weak evidence that cannabis has clinical benefits


The evidence for the effectiveness of cannabis-related products for treating chronic pain is surprisingly thin, according to a new systematic review of the evidence by researchers at Oregon Health & Science University.

The federally funded exam, which will be updated regularly, was published today in the Annals of Internal Medicine.

Researchers have found evidence to support short-term benefit in the treatment of neuropathic pain – caused by peripheral nerve damage, such as diabetic neuropathy resulting in pain described as burning and tingling, involving two synthetic, FDA-approved products containing 100% tetrahydrocannabinol, or THC: dronabinol (under the trade name Marinol) and nabilone (Cesamet). Both products also cause notable side effects, including sedation and dizziness, according to the review.

Another product, a sublingual spray of equal parts THC and cannabidiol, or CBD, extracted from the cannabis plant, known as nabiximols, has also shown evidence of some clinical benefit for neuropathic pain, although that this product is not available in the United States. side effects, such as nausea, sedation and dizziness.

“In general, the limited amount of evidence surprised us all,” said lead author Marian S. McDonagh, Pharm.D., professor emeritus of medical informatics and clinical epidemiology at the School of Medicine at OHSU. “With so much buzz surrounding cannabis-related products and the easy availability of recreational and medical marijuana in many states, consumers and patients alike might assume there would be more evidence about benefits and side effects.

“Unfortunately, there is very little scientifically valid research on most of these products,” she said. “We have seen only a small group of observational cohort studies of cannabis products that would be readily available in states that allow it, and these were not designed to answer the important questions on the treatment of chronic pain.

Voters in Oregon, Washington and 20 other states have legalized marijuana for medical and recreational use, but researchers have found that many products currently available in US dispensaries have not been well-researched.

“For some cannabis products, such as whole plant products, data are sparse with imprecise effect estimates and the studies had methodological limitations,” the authors write.

This situation makes it difficult to refer patients.

“Cannabis products vary widely in chemical composition, which could have important effects in terms of benefit and harm to patients,” said co-author Roger Chou, MD, director of Pacific Northwest Evidence-based Practice Center at OHSU. “This makes it difficult for patients and clinicians, as the evidence for one cannabis product may not be the same for another.”

The live exam, including a visual summary of the results, will also be shared on a new web-based tool launched by OHSU and the VA Portland Health Care System earlier this year to help clinicians and researchers assess the latest evidence. regarding the health effects of cannabis. Known as Systematically Testing the Evidence on Marijuana, or STEM, the project includes “clinician briefs” to help healthcare workers translate clinical implications.

“This new living evidence review is exactly the type of resource clinicians need to clarify for patients what areas of potential promise, which cannabis formulations have been studied, and most importantly, key knowledge gaps,” said co-author Devan Kansagara, MD. , MCR, Professor of Medicine at OHSU School of Medicine and VA Portland Staff Physician.

Reviewers searched over 3,000 studies in the scientific literature in January this year and landed a total of 25 with scientifically valid evidence – 18 randomized controlled studies and seven observational studies of at least four weeks duration.

The effects of cannabis and related products are based on their ability to mimic the body’s own endocannabinoid system. The system is made up of nervous system receptors and enzymes that regulate bodily functions and can affect the sensation of pain. In the evidence review, the researchers sorted the product types into high, comparable, and low ratios of THC to CBD and compared their reported benefits and side effects.

Dronabinol and nabilone fall into the high THC/CBD ratio category, with 100% THC (without CBD), showing the most benefit of the products studied, with a meta-analysis of the six randomized controlled studies showing benefit statistically valid for relieving neuropathic pain compared to a placebo.

“Honestly, the best advice is to talk to your GP about possible treatments for chronic pain,” McDonagh said. “If you want to consider cannabis, you need to talk to your doctor about it.”

In addition to McDonagh, Chou, and Kansagara, co-authors included Benjamin J. Morasco, Ph.D., Jesse Wagner, MA, Azrah Y. Ahmed, BA, and Rongwei Fu, Ph.D.

The project was funded by the Agency for Health Care Research and Quality of the US Department of Health and Human Services, contract number 75Q80120D00006. The statements contained in the report should not be interpreted as an endorsement by the AHRQ or the Ministry of Health and Social Services.


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