A large review of cannabis research found weed may reduce chronic pain but not CBD

• A US-backed review found some cannabis products can lead to improvements in patients with chronic pain.
• Treatments that led to pain improvements also had increased risk for dizziness and sedation.

In the last decade, CBD — a cannabis component that does not get you "high" — has exploded in popularity as a treatment for pain and recovery.

However, there is very little research to back this up.

In fact, a new, large-scale review of the latest cannabis research found there is some evidence weed can ease chronic pain — but researchers found treatments high in THC, which does trigger a high, to be most effective.

The review, published today and funded by the US Department of Health and Human Services, included 25 studies that each measured the impact of different compounds within the cannabis plant. Treatments made in a lab that had a high level of THC relative to CBD had "moderate improvements" in chronic pain patients. Products extracted from the cannabis plant that had around the same ratio of THC and CBD produced "small improvements" for these patients.

Marian S. McDonagh, a professor at the Oregon Health & Science University Hospital and the review's lead researcher, told Insider she signed on to do this review after Congress requested the study.

She said she was motivated to find some clear answers that would help people decide the right strains for them — but her team was stunned by the limitations of each study, and how little quality data existed on cannabis.

"What surprised us was the lack of evidence on cannabis plant-based products," she said — especially when it comes to "whole plant cannabis," as opposed to synthetic cannabis. "There's just really very little evidence and nothing you could really try to make any decision based on."

The more effective cannabis products were associated with higher risk for psychosis and dependence

The two types of products that led to pain improvements — lab-derived treatments with high THC, and products with about the same CBD and THC — were associated with a moderate to large increased risk of side effects. The side effects included dizziness, sedation, and nausea.

The risk for psychosis, cannabis use disorder, and cognitive deficits were not reported in the studies.

McDonagh said her team would encourage doctors prescribing these products for chronic pain to keep a close eye on their patients to screen for cannabis use disorder.

"If you are willing to go down the path and you want to try cannabis as a treatment for chronic pain, they're going to have to keep a really close eye on how things are going over time, especially after three months," she said.

Very little evidence that CBD can treat pain due to 'tiny and very flawed' studies

McDonagh and her team selected 25 rigorous studies for the review. Eighteen of the studies were placebo-controlled clinical trials, and seven were observational. Most patients enrolled in the studies had forms of moderate neuropathic pain, and were white and middle-aged.

They categorized the treatments into five groups:

• High THC relative to CBD, either produced in a lab or extracted from the plant
• Comparable THC to CBD ratios, in the form of sprays or oral tinctures
• Low THC relative to CBD, in the form of topical or oral products
• Whole plant products without measured cannabinoids in the form of cannabis flowers, leaves, and buds
• Non-THC or CBD cannabinoids extracted from the plant

McDonagh said though evidence that CBD has an impact on pain management is scarce, the studies done on CBD-only products were "tiny and very flawed."

McDonagh said all cannabis studies — for both THC and CBD — should run longer: all of the clinical trials evaluated were short-term, measuring the effect of treatment within one to six months.

There should be more of them, too, McDonagh said.

"The majority of these studies were only 12 weeks in duration," McDonagh said. "We know from our other work that the effects can really change over time, you may have a good effect in the beginning and then have it dissipate and you're left with side effects."

McDonagh said readers of the study should be aware of the limitations of current cannabis research, and to take the findings of potential benefits "with the grain of salt." Better and more research on the topic will make the relationship between cannabis and chronic pain management more clear.

"We are hopeful that this will also stimulate more research and we may have better things to say in the coming months or years," she said.