PALM SPRINGS, CA — Low-dose naltrexone was found to be effective and highly tolerable in women with fibromyalgia, with 57% of the participants reporting at least 30% in pain reduction, according to results of a placebo-controlled, double-blind trial presented during the 2012 American Academy of Pain Medicine Annual Meeting.

Previously, a single-blind pilot study in ten women with fibromyalgia found naltrexone 4.5mg/day reduced pain and fatigue,1 Jarred Younger, PhD, of Stanford University School of Medicine, Palo Alto, CA, and colleagues reported.

In this study, 28 women ranging from 23 to 65 years of age with a mean fibromyalgia duration of 11.7 years completed two weeks of baseline testing, 12 weeks of treatment with low-dose naltrexone (4.5mg once per day), four weeks of placebo (counter-balanced), and four weeks of follow-up. The primary outcome was daily pain. Participants used a handheld computer to complete daily symptom severity reports and were seen in the laboratory every two weeks to assess side effects and receive a new bottle of capsules. Continuation of daily medications as normal was permitted, with the exclusion of opioid analgesics.

Fifty percent of participants reported their pain being much improved or very much improved after 12 weeks of lose-dose naltrexone. Low-dose naltrexone reduced fibromyalgia symptom severity by 48.5% versus 27.4% in the placebo group (F[1101]=7.7, P=0.006), as measured in the final three days.

On a 100-point scale (100=“perfectly tolerated”), both the low-dose naltrexone (89.2) and placebo (89.4) were rated as tolerable. Vivid dreams (37% vs. 13%) and headache (16% vs. 3%) were reported more often with low-dose naltrexone than placebo. Neither fatigue nor sleep quality were improved significantly by low-dose naltrexone.

Participants were not accurate in guessing whether they were receiving low-dose naltrexone or placebo. “Low-dose naltrexone should undergo a full, parallel-group randomized controlled trial with a larger group of individuals,” the investigators noted.

1. Younger J, Mackey S. “Fibromyalgia symptoms are reduced by low-dose naltrexone: a pilot study.” Pain Med. 2009;10:663-672.