Low doses of naltrexone, a drug indicated for the treatment of opioid abuse, can reduce fibromyalgia pain, according to the results of a recent study.

The double-blind, placebo-controlled crossover study of female fibromyalgia patients (up to 90% of all U.S. fibromyalgia patients are women) builds on the findings of an earlier pilot study by the same Stanford University researchers. It had demonstrated that a daily dose of 4.5 mg of naltrexone reduced pain and fatigue in 10 fibromyalgia patients.

“This is a totally different way to treat fibromyalgia, and it seems to work for a lot of people,” said lead researcher, Jarred Younger, PhD, assistant professor in pain management and director of the Adult and Pediatric Pain Lab at Stanford University School of Medicine, in California. Dr. Younger and his colleagues presented their findings at the 2012 annual meeting of the American Academy of Pain Medicine. The American Fibromyalgia Syndrome Association funded the study.
In the new research, 30 women completed a 22-week protocol involving two weeks of baseline treatment, 12 weeks of low-dose naltrexone treatment, four weeks of placebo and four weeks of follow-up. Participants completed daily symptom severity reports via handheld computers. Patients reported significantly less pain during the weeks they took low-dose naltrexone compared with placebo (49% reduction vs. 27%). Additionally, participants rated low-dose naltrexone as tolerable as placebo. The only adverse events reported more often with low-dose naltrexone than with placebo were vivid dreams (33% vs. 13%) and headache (16% vs. 3%). Dr. Younger said only a small percentage of the dreams were described as nightmares.

At the full dose of 50 mg per day, naltrexone is used to help individuals overcome heroin dependence by blocking the pleasurable effects of getting “high.” In small doses, it suppresses the release of pro-inflammatory factors from microglia, said Dr. Younger. Microglia release chemicals that make an individual feel sick, forcing them to slow down and rest so their bodies can fight off infections. “But, theoretically, in fibromyalgia these cells are activated when they’re not supposed to be,” said Dr. Younger. “So people feel sick when nothing is invading their body.”
Another advantage of naltrexone is that it’s a generic medication, and is far less expensive than most pain medications available with a prescription: about $30 a month for patients who pay out of pocket. Because it’s not manufactured at the low dose needed for fibromyalgia treatment, patients must purchase it from a compounding pharmacy.

Fibromyalgia experts are taking note of the research. “The study showed a modest difference between patients taking low-dose naltrexone and the placebo. But most drugs for chronic pain states don’t do much better,” said Daniel J. Clauw, MD, director of the Chronic Pain and Fatigue Research Center at the University of Michigan, in Ann Arbor. “This study suggests it may be a good treatment for a subset of patients with fibromyalgia.”

Dr. Clauw does not currently prescribe naltrexone to his patients, but is considering it. “There’s enough evidence to try it on patients who aren’t responding to the other drugs, although I’d put it at the bottom of the list for now,” said Dr. Clauw. “But because it’s well tolerated and inexpensive, I might move it to the top of the list if larger, appropriately powered, double-blind trials show similar results.”

Dr. Younger is attempting to get funding for a two-year study through private donors and the National Institutes of Health. The researcher said he is especially eager to get a more powerful study under way because he has seen the positive effects of the medication on patients.

“These are people who were athletes, owned businesses and had hobbies like gardening. They can’t do those things anymore because of fibromyalgia,” said Dr. Younger. “Then they try naltrexone and go back to the activities they love. Their lives fall back into place.”