Rolling up (Image: ddp USA/REX)
Don鈥檛 expect marijuana to perform medical miracles. That鈥檚 the message from a huge review of 79 clinical trials undertaken between 1975 and 2015 that assessed the merit of taking cannabinoids 鈥� the active component in cannabis 鈥� to treat different health conditions.
Over the last 20 years, to treat many conditions, including long-term pain, sleep problems and muscle disorders.
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of the University of Bristol, UK, and her colleagues set out to examine the evidence that the drug is actually beneficial, but found little to suggest it is.
鈥淢ost trials reported greater improvement in symptoms with cannabinoids compared to control groups,鈥� says Whiting 鈥� but they didn鈥檛 usually reach statistical significance.
In addition, studies that explored the effects of medical marijuana were not always performed to a high standard. Many suffered from methodological weaknesses, such as a small sample size or incomplete data on outcomes, and substantial withdrawals of participants in half the trials. Any of these factors could have skewed the results.
Studies of a moderate standard supported the view that taking marijuana provides benefits for chronic pain relief and for muscle problems associated with conditions such as cerebral palsy. Studies of a lower standard have reported positive effects for treating sleep problems, Tourette鈥檚 syndrome, sickness from chemotherapy and weight gain in people with HIV.
Medical marijuana is also taken by some people with conditions such as depression, although Whiting鈥檚 review found little to no scientific evidence that this is beneficial. 鈥淲e found no studies in patients with depression, and only one or two small studies in patients with anxiety disorder, psychosis or glaucoma,鈥� says Whiting. This doesn鈥檛 mean that cannabinoids are ineffective for treating these conditions, she says 鈥� just that there is not yet enough evidence to reach any firm conclusions.
Trial bypass
Whiting says that cannabinoids have generally been approved for medical applications without having to go through the strict proof-of-benefit trials used to judge other medicines.
鈥淚 think cannabinoids should be evaluated in the same way as any other type of medical treatment,鈥� she says. 鈥淚t鈥檚 important that all interventions are judged by the same standards, so the potential benefits and adverse effects of cannabinoids should be considered in the light of the evidence.鈥�
The call for proper, thorough trials is echoed by and at the Yale University School of Medicine in New Haven, Connecticut, in an accompanying commentary. They say there is a failure to test the drugs in the same way as others, through the US Food and Drug Administration, which is akin to 鈥減utting the cart before the horse鈥�.
鈥淚f a state鈥檚 initiative to legalise medical marijuana is merely a veiled step towards allowing access to recreational marijuana, then the medical community should be left out of the process,鈥� says D鈥橲ouza. 鈥淐onversely, if the goal is to make marijuana available for medical purposes, then it鈥檚 unclear why the approval process should be different from that used for other medications.鈥�
In a further blow to medical marijuana, a study in the same issue of JAMA found that edible cannabinoid pills often contained incorrectly labelled dosages. Of 75 products purchased, only 17 per cent were correctly labelled, with 60 per cent containing more than stated and 23 per cent less than stated of the active ingredient.
Journal reference: JAMA, DOI:
