Absent from much of the debate so far, however, is scientific evidence to establish whether marijuana really works to relieve chronic pain; and if it does, whether it does so in a manner that is distinct from simply providing the well-known high that has made it a popular recreational but illicit drug.
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The use of marijuana for a few carefully selected medical conditions has generated heated discussion, pitting those who favour legalization against those who warn about the undesired consequences of wider availability. Absent from much of the debate so far, however, is scientific evidence to establish whether marijuana really works to relieve chronic pain; and if it does, whether it does so in a manner that is distinct from simply providing the well-known high that has made it a popular recreational but illicit drug. This edition of HealthWatch takes a closer look at the burden of chronic pain and a recent study that has received a great deal of attention.
What is neuropathic pain?
For the sake of differentiation, let’s take a look at two main types of pain: non-neuropathic and neuropathic. Non-neuropathic pain is more common and is caused by such things as bumps, bruises, sprains, fractures and inflammation caused by arthritis.
Neuropathic pain, on the other hand, is the result of injury or abnormal signals coming from the peripheral nervous system -that is, the nerves outside of the brain or spinal cord. Neuropathic pain can occur as the result of such conditions as shingles, cancer, phantom limb pain, the phenomenon known as entrapment neuropathy -in which a nerve is pinched (as occurs in carpal tunnel or chronic back pain syndromes) — and peripheral neuropathy, which is common among diabetics.
The symptoms of neuropathic pain include a constant gnawing pain, as well as a shooting and burning sensation, or tingling and numbness. No matter how you describe it, its effects can be debilitating, causing tremendous physical and emotional suffering and loss of quality of life. Not surprisingly, patients who suffer from neuropathic pain experience high rates of depression and insomnia. Neuropathic pain is frequently chronic, sometimes lasting months or even years. While complete cures are unlikely, it can be controlled with the proper treatment.
How might THC work?
The substance known as tetrahydrocannabinol (or THC), which was the subject of the study we are looking at, belongs to the family of compounds known as cannabinoids, which are closely related to pain-relieving molecules released by our own bodies. THC is the cannabinoid extracted from the Cannabis sativa (hemp) plant commonly known as marijuana, or pot.
The medical use of cannabis or marijuana is not new. Cannabis sativa has been used to treat pain since the third millennium BC. Between 10 and 15 per cent of patients with chronic pain caused by a variety of conditions, including multiple sclerosis, currently smoke cannabis for its seemingly helpful effects.
Ware MA, Wang T, Shapiro S, et al. Smoked cannabis for chronic neuropathic pain: a randomized controlled trial. CMAJ, August 30, 2010. DOI:10.1503/cmaj. 091414.
What was unique and important about this study?
Investigators at McGill University undertook a remarkable challenge in conducting this study. In addition to dealing with the enormous regulatory hurdles to performing research on cannabis, the team needed to develop a true placebo, or pretend cannabis, that would be indistinguishable from the real McCoy to determine the exact effects of the THC without a psychological effect. The study tested four potencies ranging from the zero per cent placebo dose to a 10 per cent THC concentration.
The researchers managed to recruit 23 neuropathic pain patients who were suffering from pain arising from an earlier injury or a surgical procedure. They were randomly assigned to the four dosing regimens and took a single inhalation of the smokable capsules provided to them containing the active ingredient or placebo, three times a day for two separate five-day periods.
Of key interest to the researchers was whether there would be a reduction in the severity of the pain that the subjects experienced. However, the researchers also measured other parameters: levels of anxiety, depression and the ability to sleep restfully. The investigators also wanted to know whether subjects experienced a high from the test drug.
What did the study show?
The highest potency of THC reduced the level of pain by a modest amount, while the weaker preparations had only marginal effects. In addition, the higher levels of THC improved the subjects’ ability to fall asleep and led them to report a more restful night. There was no apparent effect on overall mood, nor any evidence of this small exposure to cannabis leading to a perceived high.
What does this mean for those suffering from neuropathic pain?
While the McGill study is a welcome addition to what is a fairly sparse number of well-done studies, there is still more to learn about how to make cannabis as acceptable and as safe as possible. In the meantime, a patient’s autonomy in making the best decision for his or her particular circumstance should be paramount, and this study provides some guidance in that regard.
How can patients obtain THC legally?
Synthetic cannabinoids are sold in Canada in pill form as Marinol and Cesamet. While in most countries it is illegal to smoke cannabis for recreational use, as a medicine it is legal in Canada, Germany, the Netherlands, Spain and Israel, among other countries. To legally smoke marijuana, one has to find a doctor willing to sign a prescription for the drug. Health Canada then approves the possession licence, and the prescription is filled by growing a small supply of marijuana or by buying it from Health Canada. The organization estimates that approximately 4,000 Canadians have been granted a licence to possess marijuana legally.
The material provided in HealthWatch is designed for general educational purposes only and does not pertain to individual cases. It should not replace necessary medical consultations with your own doctor or medical professional.