Several other systematic reviews have recently evaluated cannabinoids for treating chronic pain, but the new study’s methodology was “distinct” in “important ways,” leading to “conclusions that differ from other reviews,” according to the authors of the paper published in the Annals of Internal Medicine.
Dr. Marian S. McDonagh
In the new systematic review, synthetic products with high THC:CBD ratios were associated with moderate improvements in pain, whereas plant-based products with comparable THC:CBD ratios offered less relief, said study author Marian S. McDonagh, PharmD, professor of medical informatics and clinical epidemiology, and codirector of the Evidence-based Practice Center at Oregon Health & Science University, Portland, and colleagues.
Specifically, the investigators stratified cannabis-based interventions according to relative content of two key cannabinoids: THC and CBD. Products were sorted into five categories: high THC:CBD ratio (at least 2:1), comparable THC:CBD ratio (less than 2:1 but more than 1:2), low THC:CBD ratio (no more than 1:2), whole-plant cannabis products, and other cannabinoids.
“In preclinical studies, THC and related compounds have demonstrated analgesic properties, although its psychoactive effects and addiction potential may limit its suitability as an analgesic,” the investigators wrote. “CBD and other cannabinoids may also have some analgesic or anti-inflammatory properties and are not believed to be psychoactive or addictive. Given the variation in analgesic effect with THC and CBD, response may differ according to the ratio of THC to CBD in products used to treat pain.”
The final analysis included 18 randomized placebo-controlled trials involving 1,740 individuals and 7 cohort studies involving 13,095 individuals. Most of the studies were short-term, lasting 1-6 months.
Pain was scored on a ten-point scale, with improvements reported as the mean difference from baseline to post treatment. A mean difference in pain score of 0.5-1.0 was considered a “small effect,” an improvement of 1-2 points was considered a “moderate effect,” and an improvement greater than 2 points was considered a “large effect.”
Cannabis-based products with relatively high THC:CBD ratios showed efficacy
Synthetic products with high THC:CBD ratios offered moderate pain relief, based on a mean difference in pain score of –1.15 (95% confidence interval, –1.99 to –0.54), whereas products with comparable THC:CBD ratios were associated with a small effect on pain, with a mean difference of –0.52 (95% CI, –0.95 to –0.19).
According to Dr. McDonagh, treatment response rates were on par with response rates for more conventional treatments, “such as opioids or specific antidepressant drugs,” but data for the cannabis-based products are weaker.
“The amount of evidence available for cannabis-related products is very limited for [response rates], and therefore less certain,” Dr. McDonagh said in an interview. “The average reduction in pain severity is also similar to some other treatments, but we do not have studies directly comparing these treatments to draw conclusions.”
Although the cannabis-based products with relatively high and comparable THC:CBD ratios showed efficacy, they were also associated with “moderate to large increased risk for dizziness, sedation, and nausea,” the investigators wrote, noting that evidence was insufficient to characterize other “key adverse event outcomes” that may occur with long-term use, such as “psychosis, cannabis use disorder, and cognitive deficits.”
For products with low THC:CBD ratios, or without reported THC:CBD ratios, data were too scarce to reach any conclusions at all about safety or efficacy, highlighting the sizable knowledge gaps that remain in the area, the authors said.
“The current evidence on cannabis-related products for chronic pain is quite limited,” Dr. McDonagh said in an interview. “Patients with chronic pain should consult with their doctor to discuss which of the many options for treating chronic pain is best for them to start with.”