The final study reviewed included 74 patients with knee OA who received a fatty acid amide hydrolase-1 (FAAH-1) inhibitor called PF-04457845, which was compared with naproxen.5 However, the study stopped because of futility. “While naproxen showed reduction in pain compared to placebo, the FAAH-1 inhibitor did not demonstrate difference from placebo, although the agent was well tolerated, with a safety profile similar to placebo,” the authors wrote.
The use of an FAAH-1 inhibitor has not yet been studied in inflammatory rheumatic conditions or fibromyalgia, the authors reported. They also did not find any studies of dronabinol or herbal cannabis in patients with rheumatic disease.
Significance
With the results of the four studies so varied, the review authors had a hard time making any solid conclusions. “This systematic review has revealed a dearth of studies examining the effects of cannabinoids in a small number of patients with rheumatic disease,” the authors wrote. “No comment can be made regarding effects for herbal cannabis preparations in patients with rheumatic diseases.”
Although the studies did find some statistical improvements in pain and sleep, the side effects of altered perception, dizziness, drowsiness and some gastrointestinal issues are still troublesome, the authors wrote. In fact, for the three completed studies, 25–50% of patients experienced side effects, such as dizziness, drowsiness and cognitive effects; many also reported dry mouth, nausea and constipation. However, there were no serious adverse events in the active treatment groups.
It’s also particularly surprising that with the prevalent use of medical herbal marijuana in the U.S. and Canada, not a single study has been conducted on the effects of marijuana in those with musculoskeletal complaints, Dr. Fitzcharles said.
The Implications
Despite the lack of conclusive evidence from the review, rheumatologists must still be prepared to give patients some guidance on the use of marijuana for their condition. “Rheumatologists will be caring for patients who will be using marijuana, often by self-medication, with or without the knowledge of the treatment physician,” Dr. Fitzcharles said. “This is a current reality and will likely be an increasing practice in the future.”
Rheumatologists need to be educated about the effectiveness of cannabinoids to properly advise patients, she said. “It will be important to maintain a level-headed approach, bolstered by critical appraisal of the literature, and not be swept away by public opinion and advocacy. In the absence of evidence in the rheumatology patient population, we must take note of the current knowledge of both the immediate and long-term risks of marijuana use, mostly derived from studies of recreational users,” she added.
