Researchers involved in a federally funded review of scientific literature on the effectiveness of cannabis products to treat chronic pain found evidence to support short-term benefits.

The review, which will be updated on an ongoing basis, was conducted by researchers from the Oregon Health & Science University (OHSU) and published June 6 in the Annals of Internal Medicine. It was funded by the Agency for Healthcare Research and Quality, one of 12 agencies within the U.S. Department of Health and Human Services.

Specifically, OHSU reviewers found evidence to support that two FDA-approved synthetic products made of 100% THC provided interim benefits in treating neuropathic pain—caused by damage to peripheral nerves, such as diabetic neuropathy resulting in pain described as burning and tingling, according to an OHSU news release. Those products were dronabinol (under the trade name Marinol) and nabilone (Cesamet).

Dronabinol and nabilone are used to treat nausea and vomiting caused by cancer chemotherapy, according to the National Institute of Health (NIH).

Another product, nabiximols, which was approved in 2010 as a botanical drug in the United Kingdom (and is not available in the U.S.), also showed evidence of some clinical benefits for neuropathic pain, according to OHSU reviewers. Nabiximols (Sativex) is an extract sold as a mouth spray and contains a 1-to-1 ratio of THC and CBD. It’s used for treatment of neuropathic pain from multiple sclerosis and for intractable cancer pain, according to NIH.

Nabiximols was developed by GW Pharmaceuticals, a manufacturer that also developed Epidiolex. When Epidiolex was approved by the U.S. Food and Drug Administration in June 2018 for the treatment of seizures associated with two rare forms of epilepsy that affect young children, it became the first plant-derived cannabinoid prescription medicine.

The OHSU abstract of the published review notes that the study had significant limitations and that evidence on other products was insufficient or lacking. In addition, OHSU reviewers said they needed more research to make conclusions on long-term effects.

“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. “With so much buzz around cannabis-related products, and the easy availability of recreational and medical marijuana in many states, consumers and patients might assume there would be more evidence about the benefits and side effects.”

She added, “Unfortunately, there is very little scientifically valid research into most of these products. 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.”

OHSU reviewers searched more than 3,000 studies in the scientific literature as of January 2022, and said they landed on a total of 25 with scientifically valid evidence—18 randomized controlled studies and seven observational studies of at least four weeks.

FDA-approved dronabinol and nabilone showed the most benefit among the products studied, according to OHSU reviewers.