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   Sep 04

Experts Say Cannabis for Pain Requires Better Science

Paris—Although medical marijuana (Cannabis sativa) is now prescribed in 23 states in the United States for pain relief for musculoskeletal and arthritic conditions, cancer, headache and other conditions, there is limited evidence to support its use, say some experts. This is especially true for use in individuals with musculoskeletal complaints.

Further research is needed to clarify the mechanisms of action of the various cannabinoid molecules as well as the potential for clinically relevant therapeutic effects, according to a presentation at the 2014 European League Against Rheumatism Con gress. This research can lead to improved awareness of the potential benefits and risks of the various components of marijuana for the treatment of pain.

“When thinking of herbal cannabis specifically, there are currently no studies in patients with rheumatic conditions that can assist physicians to competently and safely advise patients,” said Mary-Ann Fitzcharles, MB, ChB, Division of Rheumatology and Alan Edwards Pain Management Unit, McGill University, Montreal, Quebec, Canada. “Unfortunately, various jurisdictions have required physicians to accept responsibility for prescribing herbal cannabis, or for caring for patients who may be using medicinal herbal cannabis in the absence of sound advice. Therefore, in the absence of the usual [research] that is required for any other therapeutic agent worldwide, physicians must project a message of extreme caution that should focus on the need to protect both the patient and society.”

The only information on herbal cannabis use in rheumatic conditions is based on a few small population studies of “users,” with self-reported diagnosis and self-reported outcome measures, Dr. Fitzcharles said. Furthermore, there is little information on the quantity or quality of the agent used, and methods of administration, as well as often a lack of clarity for true reasons for use, as many users report previous recreational marijuana use.

The need for further research is clear, she continued, especially for pain in rheumatic conditions. There is only one quality study on the role of nonherbal cannabinoids in rheumatoid arthritis, for example, and only five in fibromyalgia, she told meeting attendees; of those eight studies, only three were identified as randomized controlled trials.

A recent survey of family physicians in the state of Colorado, where marijuana is legally prescribed, showed that most respondents were not convinced of the benefits of marijuana and wanted further education about it (J Am Board Fam Med 2013;2:52-60).

The general term “cannabinoids” includes endocannabinoids (naturally occurring in bodily systems), phytocannabinoids from the plant (herbal marijuana) and synthetocannabinoids (pharmaceutical preparations). Among the components of cannabinoids, delta-9-tetrahydrocannabinol (Δ9-THC), commonly referred to as THC, is psychoactive, whereas cannabiol is weaker in this regard and may have considerable therapeutic effects.

Herbal cannabis is most often inhaled, either smoked or via a vaporizer, but can also be ingested in baked products or as a tea infusion. The oromucosal spray of nabiximols, a combination of Δ9-THC and cannabidiol, is a pharmacologic preparation sprayed under the tongue.

Pharmacologic preparations are more desirable than herbal ones, said Dr. Fitzcharles; the former are controlled regarding quality and dosing, and have been evaluated for efficacy and safety, whereas the latter are largely uncontrolled. Pharmacologic preparations are more likely to deliver quantifiable and consistent amounts of active drug than herbal cannabis. Additionally, they avoid the negative health effects associated with smoked herbal cannabis, due to the inhalation of polycyclic aromatic hydrocarbons, tar and carbon monoxide.

Other health risks associated with use of herbal cannabis include compromised cognition and psychomotor function (a risk associated with higher rates of driving accidents), cardiovascular effects (tachycardia and hypotension) and long-term risk to respiratory function and psychological health.

“It’s a myth that one can’t become dependent on cannabis,” said Dr. Fitzcharles. “Dependence occurs in at least 8% of recreational users by one year, and may alert society to the abuse potential of pharmacologic preparations. Some of the pharmaceutical cannabinoid products—dronabinol and nabiximols—also have modest abuse potential.”

Endocannabinoids are found throughout the body. There are two endocannabinoid receptors: The CB1 receptor is found in the nervous system and in joint tissue and has effects on pain and bone health, whereas the CB2 receptor is found mostly on immune cells with less understood function.

“The presence of both receptors and endocannabinoid ligands in joint tissue indicates that the endocannabinoid system is probably important in rheumatic diseases,” Dr. Fitzcharles said.

Herbal cannabinoids pose many unanswered health-related and societal questions, she added. Their potential risks and benefits suggest that research is needed to identify compounds with more targeted effects and fewer psychoactive and other negative effects. Dr. Fitzcharles urged health professionals to advocate for more research.

Commenting on the presentation, Neal Birnbaum, MD, Division of Rheumatology, California-Pacific Medical Center, in San Francisco, agreed that more research is needed and said that more responsible prescribing by doctors is also required.

“It is common for physicians to prescribe narcotics and medical marijuana in my state, where it is legal,” Dr. Birnbaum said. “But this is often done loosely without considering all the risks and benefits. There can be serious consequences with little benefit.”

—Alice Goodman

Source: Pain Medicine News

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