Rheumatologists should not currently be recommending the use of medical marijuana to their patients for relief of chronic pain, researchers stated. Among the reasons for this advice are acute and chronic risks, a lack of evidence for efficacy, and the absence of data on appropriate dosing, according toMary-Ann Fitzcharles, MD, of McGill University in Montreal, and colleagues.
Advocacy for access to cannabinoid treatments has led to a societal groundswell with regulatory bodies around the globe considering the legalization of herbal cannabis for medicinal use," Fitzcharles and colleagues wrote online in Arthritis Care & Research
And with 20 states now having legalized it, rheumatologists need to be prepared to answer patients' questions based on the best available information and evidence, the authors stated.
Surveys have suggested that arthritis pain is one of the most common reasons patients use medical marijuana, and has been the stated diagnosis for two-thirds of Canadians who are authorized users.
The plant has been used for centuries for pain relief, as well as for effects on sleep and mood that are largely mediated through the interaction of tetrahydrocannabinol (THC) with receptors of the endocannabinoid system.
One major obstacle to the acceptance of medical use is the wide variation of active compounds in the plant, with THC concentration ranging from 1% to 30% of the plant and blood levels among individuals who inhale it that range from an estimated 7 ng/mL to 100 ng/mL.
In addition, even in locales where legal, most users obtain marijuana illegally, the researchers reported.
"Therefore, the lack of the most elementary requirements for responsible drug administration must call into question any use of herbal cannabis for rheumatic pain treatment at this time," they stated.
Evidence for efficacy in rheumatologic disease is sparse to date. One randomized trial tested a cannabis-based medicine known as nabiximol (Sativex) in 58 patients with rheumatoid arthritis, and found significant benefits for morning pain both with movement and at rest, sleep quality, disease activity scores, and patients' experience of pain.
In two studies of another synthetic form of THC, patients with fibromyalgia had improvements in painand sleep benefits similar to what was seen for amitriptyline.
Otherwise, surveys have relied on self diagnosis and treatment, and no formal study of the plant-based safety or efficacy in rheumatology has been done.
"While there is good evidence for efficacy of cannabinoids for treating some chronic pain conditions, such as cancer and neuropathic pain, these pain types have different underlying mechanisms from the mostly peripheral/nociceptive pain in rheumatic diseases," the researchers pointed out.
Among the potential hazards associated with marijuana use are effects on cognitive and psychomotor functioning, with slowing of reaction times and motor control and impairments in short term memory that can persist for hours.
A particular concern is for driving. The authors noted that relevant impairments can last up to a full day after a single ingestion, according to Health Canada, and emphasized the importance of driving for preservation of function and independence among patients with conditions such as arthritis.
Other risks include possible effects on mood, and particularly depression, and the possibility of dependence. In addition, a long-term study of Swedish youth found that frequent users had a more than two-fold increased risk of lung cancer.
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