PORTLAND, Ore. (KOIN) – There’s “surprisingly thin” evidence to back the effectiveness of cannabis-related products to treat chronic pain, according to Oregon Health & Science University researchers who recently reviewed scientific literature on the topic

Scientists say their research found cannabis products can cause short-term reductions in chronic pain, but little else.

“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,” said Marian McDonagh, a doctor of pharmacy at OHSU. 

However, the evidence is slim. 

Researchers looked at both tetrahydrocannabinol, or THC, and cannabidiol, or CBD, products. 

They found evidence indicating two FDA-approved synthetic products, dronabinol and nabilone, which are made of 100% THC, are both effective as short-term treatments for neuropathic pain caused by damaged peripheral nerves. This includes diabetic neuropathy, which results in burning and tingling pain. 

Although effective, these products can also cause side effects such as sedation and dizziness. 

Another product, made of equal parts THC and CBD, known as nabiximols, proved effective at providing some benefit for neuropathic pain. The product is not available in the U.S. and also led to side effects like nausea, sedation and dizziness. 

Dr. McDonagh said the limited amount of evidence about the effectiveness of cannabis products surprised OHSU researchers. 

“Unfortunately, there is very little scientifically valid research into most of 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.” 

Recreational marijuana is legal in 19 states and Washington DC and medical marijuana is legal in 38 states and Washington DC. 

However, researchers found many of the products available for purchase at U.S. dispensaries have not been well studied and that the data are sparse for some cannabis products.  

The limited available information or evidence on cannabis products could be due, in part, to the fact that marijuana remains a schedule 1 drug. This classification means the Drug Enforcement Administration can limit its supply and make it more difficult to research. This limits the researchers’ ability to study a drug for medicinal value. 

Researchers who took part in the review searched more than 3,000 studies in the scientific literature and found 25 with scientifically valid evidence. Of those, 18 were randomized controlled studies and seven were observational studies of at least four weeks. 

“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 Dr. Roger Chou, who co-authored the review. “That makes it tough for patients and clinicians, since the evidence for one cannabis-based product may not be the same for another.” 

In the evidence they reviewed, researchers sorted the types of products into high, comparable and low ratios of THC to CBD, and compared their reported benefits and side effects. 

Dronabinol and nabilone fit into the high THC-to-CBD ratio category. Both products are 100% THC and include no CBD. They showed the most benefit among the products studied. 

OHSU researchers say the best advice they have for people is to talk to their primary care physicians about possible treatments for chronic pain, including cannabis treatment.