At best, only moderate-quality evidence supports the use of medical cannabinoids, and for only two conditions. And low-quality evidence only “suggests” that these agents may improve other medical conditions, but that limited effectiveness applies only to the four conditions that have been studied, according to a report published online June 23 in JAMA.
This doesn’t necessarily mean that cannabinoids have poor efficacy but instead likely reflects the dearth of high-quality research into their medical usefulness.
In what they described as the first comprehensive review to evaluate the efficacy of numerous cannabinoids across a broad range of indications, researchers analyzed data from 79 studies involving 6,462 participants performed from 1975 to early 2015. The studies assessed nabilone, dronabinol, nabiximols, levonantradol, THC, THC/CBD, and ajuvenic acid, delivered via oral capsules, cigarettes, vaporizers, oromucosal sprays, or intramuscular injection, said Penny F. Whiting, Ph.D., of University Hospitals Bristol (England) and her associates.
Most of the studies suggested that cannabinoids improved symptoms for nearly all the 10 medical conditions included in this meta-analysis, but most of the studies were of poor quality so their conclusions were questionable. These agents’ efficacy did not vary according to the type of cannabinoid assessed or the mode of delivery.
Moderate-quality evidence indicated that cannabinoids may be beneficial for chronic neuropathic or cancer pain, and moderate-quality evidence indicated that they may also be beneficial for spasticity due to multiple sclerosis or traumatic paraplegia. Low-quality evidence suggested that cannabinoids may improve nausea and vomiting due to chemotherapy, may improve appetite and induce weight gain in HIV infection, and may improve sleep in primary sleep disorders as well as in conditions that disrupt sleep such as fibromyalgia, multiple sclerosis, and chronic pain. Very low-quality evidence (due to extremely small sample sizes) suggested that cannabinoids may greatly improve tic severity in Tourette’s syndrome, Dr. Whiting and her associates said (JAMA 2015 June 23 [doi:10.1001/jama.2015.6358]).
Otherwise, the evidence did not support cannabinoids’ efficacy in anxiety, depression, psychosis, or glaucoma. Adverse events included asthenia, problems with balance, confusion, dizziness, disorientation, dry mouth, fatigue, and somnolence.