An inexpensive, generic drug currently used to treat alcohol and drug addiction may offer relief to people who have fibromyalgia.

In a small pilot study, Stanford University researchers gave the drug naltrexone or a placebo to 10 women with a diagnosis of fibromyalgia over 14 weeks. 

By the end of the study, participants reported 30 percent greater improvement in their fibromyalgia symptoms when they took the naltrexone compared how they felt when they were taking the placebo.

Jarred Younger, PhD, an instructor of anesthesia and pain management at the Stanford University School of Medicine in Palo Alto, Calif., who was the lead researcher on the study, admits that the decision to try naltrexone for fibromyalgia appears, at first blush, to be counterintuitive.

That’s because naltrexone, a drug that has been used for 30 years to treat alcohol and drug addiction, works by blocking the affects of opioids on the brain; and opioids kill pain.

But Younger says that in smaller doses, the drug may have a different effect, switching off cells called microglia.

“Microglia are normally really good cells to have,” Younger says, “They’re our brain’s immune system cells, and when they detect a virus or something they become activated, and they produce a number of chemicals that help fight off the infection, but they also produce chemicals that make us feel really sick.”

Younger’s hypothesis is that in fibromyalgia, microglia may be switched on, and stay on, even when there’s no infection to fight. “So we think fibromyalgia is an immune system disorder,” he says.

Younger says he got the idea to study naltrexone because of the successes reported by a group of doctors in New Jersey who had tried it on their patients who have the puzzling condition, which is characterized by widespread pain and fatigue.

“I’ve seen too many people with fibromyalgia who have tried everything and they don’t work, and they’re suffering,” he says. “And it’s a lot of people who are still suffering.”

Younger thinks there may be alternative treatments or off-label treatments, such as naltrexone, that work for fibromyalgia, but they wouldn’t ordinarily be studied because there isn’t enough money to be made from their development.

His pilot study, which was published in the April 17, 2009, issue of the journal Pain Medicine, was supported, in part, by a grant from the Arthritis Foundation.

For this initial investigation, researchers recruited 10 women with a clinical diagnosis of fibromyalgia and had them take 4.5 milligrams of naltrexone or a placebo daily for 14 weeks. Each participant took both the drug and the placebo, so they acted as their own control subjects, but they were not told which weeks they were taking a placebo and which weeks they were given naltrexone.

Each of the women had a hand-held computer and used it to report daily symptoms of pain, fatigue, sadness, stress, sleep quality, the ability to think and remember, gastrointestinal symptoms and headaches. Participants were also evaluated in a lab every two weeks to obtain their mechanical, heat and cold pain thresholds.

During the placebo phase of the study, symptoms were reduced an average of only 2.3 percent. During the weeks when the women were taking the naltrexone however, their symptoms improved by 32.5 percent. Their lab-tested pain tolerance also increased on naltrexone, but did not improve when they took the placebo.

Minimal side effects were reported in the study. Two participants reported experiencing vivid dreams while on the medications and one reported nausea and insomnia for a few nights that eventually went away.

The naltrexone was so beneficial for some study participants that they continued to take it and see further improvement after the study ended, Younger says.

The Stanford researchers have been so encouraged that they are currently mounting a larger, longer double-blind study to see if their first results will hold.