Naltrexone isn't a new drug; it's been around for more than 30 years and is used to treat opioid addiction.
Stanford's Jarred Younger, PhD, and Sean Mackey, MD, PhD, tested a low dose of naltrexone as a fibromyalgia treatment in 10 women who had had fibromyalgia for about 10 years, on average.
First, the women spent two weeks recording the severity of their fibromyalgia symptoms every day using a handheld computer. And they took lab tests to gauge their fibromyalgia pain and sensitivity to heat and cold.
After that, the women took a placebo pill every day for two weeks, but they didn't know it was a placebo pill. At the end of the placebo period, the women took a naltrexone pill once a day for eight weeks. Finally, they spent the last two weeks of the study not taking naltrexone or the placebo.
All along, the women continued to rate their fibromyalgia symptoms every day, and they repeated their lab tests every two weeks.
While taking the placebo, the women reported a 2.3% drop in the severity of their fibromyalgia symptoms, compared to their symptom ratings at the start of the study.
When they switched from the placebo to naltrexone, they reported an additional 30% drop in their fibromyalgia symptom severity.
The women also showed greater tolerance for pain and for hot (but not cold) temperatures while taking naltrexone.
Most of the women -- six out of 10 -- responded to naltrexone.
Side effects were mild and brief.
Two women reported having more vivid dreams during the study, and one woman reported transient nausea and insomnia during the first few nights of taking the pills, note Younger and Mackey.
The study, which appears online in Pain Medicine, was a small, preliminary project to see if low-dose naltrexone showed promise. It did, so Younger and Mackey are already working on a new study that will test low-dose naltrexone in 30 fibromyalgia patients for 16 weeks.
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