THC products provide small improvements in pain but carry side effects

A new systematic evidence review finds that cannabis products that carry relatively high levels of the psychoactive compound tetrahydrocannabinol, commonly known as THC, may provide short-term improvements in pain and function. 

However, the review found THC-based products led to an increased risk of common adverse symptoms like dizziness, sedation and nausea. 

At the same time, the review found that recent randomized controlled trials involving products mainly or only containing cannabidiol, or CBD, which does not have psychoactive properties, demonstrated almost no improvement in managing pain. 

This may be surprising to people. Conventional wisdom was that CBD was promising because it doesn't have euphoric effects like THC and it was thought to have medicinal properties. But, at least in our analysis, it didn't have an effect on pain." 

Roger Chou, M.D., lead author, senior adviser for the Pacific Northwest Evidence-based Practice Center at Oregon Health & Science University

The cannabis plant contains both THC and CBD. Both are believed to act on the body's endocannabinoid system, which modulates pain. Many U.S. states, including Oregon, have legalized cannabis for both recreational and medicinal use, and many people have turned to cannabis to treat conditions including pain, anxiety and sleep. 

The review, an update to a living review first published in 2022, was conducted by researchers at OHSU and published today in the Annals of Internal Medicine. 

Researchers incorporated several additional short-term placebo-controlled randomized trials since the previous review. Both the original review and the new update found some evidence of pain relief for two prescribed products, dronabinol and nabilone, which are made of 100% THC or its analogue. Dronabinol and nabilone are FDA approved for treatment of nausea and vomiting due to chemotherapy, and one of them, dronabinol, is approved for HIV wasting syndrome. 

The new review found that oral THC-only products slightly reduce pain severity. 

Chou noted that the improvement in pain was relatively small - on the order of a half point to a point compared with a placebo on a 10-point pain scale. 

"It's complicated because cannabis products are complicated," he said. "It's not like taking a standardized dose of ibuprofen, for example. Cannabis is derived from a plant and has multiple chemicals in addition to THC and CBD that may have additional properties depending on where it's grown, how it's cultivated and ultimately prepared for sale." 

The medical profession is equally divided on the benefits of medicinal use of cannabis: The American College of Physicians recently declined to recommend inhaled cannabis for non-cancer pain whereas a previous expert panel issued a soft recommendation for people with chronic cancer or non-cancer pain when standard treatments did not work. 

Chou said the review's finding that CBD products failed to reduce pain will surprise many people. 

"CBD-based products are widely available in dispensaries. Many people use these products and they think it helps," he said. "Our goal is to provide some scientific basis to help people make their decisions." 

The researchers categorized cannabinoids by the ratio of THC to CBD (whether it was high, comparable or low); whether the product was synthetic (produced in a lab) or plant-based (as well as the degree of purification); and the administration method. 

The data showed that oral THC-only products slightly reduced pain severity, but that across trials they were also linked to moderate-to-large increases in dizziness, sedation and nausea. 

They concluded that more research is needed on long-term outcomes and other types of cannabis products; whether there are differences between THC-only products in effectiveness; and to better understand how results based on the products evaluated in the review apply to products that are available in dispensaries. 

In addition to Chou, co-authors included Rongwei Fu, Ph.D., Azrah Y. Ahmed, B.A., and Benjamin J. Morasco, Ph.D.