Blog | Wednesday, July 25, 2012

Cannabis for chronic pain: Are we there yet?


Marijuana is pretty popular stuff, and for good reason. It is a potent drug, capable of both making someone feel good and of reinforcing dependence pathways in the brain. Cannabis has been lauded for its ability to treat nearly any unpleasant symptom (except perhaps dry mouth), but so far evidence other than the anecdotal has been meager.

One of the areas where research has been a bit promising is in the treatment of certain types of nerve pain. Small studies have shown some possible benefit in certain groups of patients, but robust studies are lacking. In the U.S., this is certainly due at least in part to restrictions on cannabis research, but only in part.

Still, chronic nerve pain is an important problem, with imperfect treatments. Opiates such as morphine are effective but come with significant side-effects. Some anti-seizure medications such as gabapentin and pregabalin have shown some promise, but they are relatively expensive (although the price on gabapentin is dropping) and only somewhat effective. Finding effective drugs, to be used either alone or in combinations, would help people suffering from a frustrating and sometimes disabling problem.

The Canadian Medical Association Journal recently released a study on cannabis. The study focused on smoked cannabis in a subset of patients with chronic nerve pain. Cannabis and its active ingredients are available in many forms, including oral mixtures of cannabis extract and THC alone. The authors don't give a specific justification for the use of traditional pot-smoking, but the editorial that accompanies the piece suggests that: "It's good to see the trial of smoked cannabis in neuropathic pain reported by Ware and colleagues because smoking is the most common way in which patients try this drug."

I hope that this isn't the justification intended by the authors. This may be obvious to most readers, but choosing a route of delivery based on "what they do on the street" is not a terribly clever thing to do. Even raw cannabis can be delivered by (probably) safer inhaled means such as vaporization (and they do mention vaporization at the end of the paper).

In any case, the study was, in some respects, well-designed. They appeared to have a good placebo control, which is no small feat in a study of smoked cannabis. And they did find some modest improvement in pain scores, and noted that this reduction was dose-dependent. The more potent the weed, the lower the post-treatment pain score. But in total, the evidence isn't terribly convincing.

The study was very small, and the authors admit that their results were modest, especially when compared to already-available medications. They attempt to minimize this by noting that the patients chosen had already failed conventional therapy, although the study design does not suggest this to be strictly the case.

While this study gives us reason to continue to look at cannabis, it does not give convincing evidence that cannabis improves upon currently available drugs in regards to safety and efficacy.

References

Mark A. Ware MBBS, Tongtong Wang PhD, Stan Shapiro PhD, Ann Robinson RN, Thierry Ducruet MSc, & Thao Huynh MD, Ann Gamsa PhD, Gary J. Bennett PhD, Jean-Paul Collet MD PhD (2010). Smoked cannabis for chronic neuropathic pain: a randomized controlled trial (Early e-release) Canadian Medical Association Journal: 10.1503/cmaj.091414

Peter A. Lipson, ACP Member, is a practicing internist and teaching physician in Southeast Michigan. After graduating from Rush Medical College in Chicago, he completed his internal medicine residency at Northwestern Memorial Hospital. This post first appeared at his blog, White Coat Underground. The blog, which has been around in various forms since 2007, offers "musings on the intersection of science, medicine, and culture." His writing focuses on the difference between science-based medicine and "everything else," but also speaks to the day-to-day practice of medicine, fatherhood, and whatever else migrates from his head to his keyboard.