POINT: Cannabis can relieve neuropathic pain.
As an oncologist, I treat cancer patients who have nausea, vomiting, weight loss, pain with and without opioids, insomnia, and depression. With cannabis, I can recommend that they try one medicine instead of five or six prescriptions that will interact either with one another or with their cancer chemotherapy.
Studies show that cannabis and cannabinoids are effective for peripheral neuropathic syndromes associated with HIV, multiple sclerosis, or posttraumatic or postsurgical causes. A study of diabetic neuropathy is ongoing; cannabis has not yet been studied for chemotherapy-induced neuropathy. Other data show that cannabis and cannabinoids may be synergistic with opioids in relief of chronic pain without altering pharmacokinetics.
We conducted a randomized, placebo-controlled study of cannabis for patients with HIV-related peripheral neuropathy at San Francisco General Hospital because preclinical studies and anecdotal patient reports said it was helpful. Average neuropathic pain scores in the week before being admitted to our research center were about 60 out of 100. After a 2-day run-in period, patients were randomized to smoke cannabis or placebo three times a day for 5 days. Among 50 patients who completed the study, neuropathic pain decreased by about 34% with cannabis versus 17% with placebo. Our threshold for a positive response was at least a 30% reduction in pain; this was reported by 52% on cannabis and 24% on placebo (Neurology 2007;68:515-21).
We also used a more objective heat-capsaicin method to assess pain. An area on the forearm was heated to 40° C for half an hour and then capsaicin (the active ingredient in chili peppers) was applied. This creates an area of hypesthesia and allodynia that can be measured using a brush and a piece of foam while the patient looks in another direction.
On the heat-capsaicin tests, the area of hypesthesia or allodynia either increased or was the same after smoking placebo but decreased approximately 30% after smoking cannabis. We calculated that the number needed to treat to get a beneficial effect was 3.6, which is equivalent to that with gabapentin, the mainstay treatment for our patients with HIV-related peripheral neuropathy.
A crossover study in 28 patients with HIV-associated neuropathy at the University of California, San Diego found that pain decreased with cannabis versus placebo. The number needed to treat was 3.5. (Neuropsychopharmacology 2009;34:672-680).
Investigators at the University of California, Davis, randomized 38 patients with central and peripheral neuropathic pain to low- or high-dose cannabis or placebo. They found a linear analgesic dose response for both doses of cannabis, compared with placebo, and reported that the effect was not due to lysis of anxiety but to reduction of core nociception as well as emotional responses to pain. (J. Pain 2008;9:506-21).
A randomized, double-blind, four-period crossover study in Montreal looked at 23 participants with postsurgical neuropathic pain who inhaled increasing dosages of tetrahydrocannabinol (THC). Results showed that the average daily pain intensity was significantly lower and quality of sleep improved in the highest-dose THC group, compared with the placebo group (CMAJ 2010;182:e694-701).
We recently completed a study funded by the National Institute on Drug Abuse to look at effects of combined use of opioids and cannabis, in which we also assessed effects on pain.
We saw a significant 26% reduction in pain with the addition of vaporized cannabis in the cohort as a whole. Pain reduction was greater in the morphine group (a 31% decrease) compared with the oxycodone group (a 23% decrease). We saw no adverse safety effects. Although we know quite well that the study was too small to make a definitive claim, this was a tantalizing demonstration of potential synergy between opioids and cannabinoids, (Clin. Pharmacotherapeutics 2011;90:844-51).
Every 10 years since cannabis was removed from the medical formulary in 1942, some august government body in the United States looks at cannabis in medicine. They all conclude the same thing – that it’s a valuable medicine, and should be available. That usually goes ignored, however. An Institute of Medicine report in 1999 said the accumulated data indicate a potential therapeutic value for cannabinoid drugs in the treatment of pain, control of nausea and vomiting, and appetite stimulation.
Dr. Donald I. Abrams is a professor of clinical medicine at the University of California, San Francisco. He declared having nothing to disclose except that he went to college in the 1960s. This debate took place at the annual meeting of the American Academy of Pain Medicine.