Low-dose naltrexone not superior to placebo for fibromyalgia pain relief

Low-dose naltrexone was not superior to placebo in relieving pain from fibromyalgia in women, although it might improve memory problems, a study found.

Researchers assessed whether 12-week treatment with low-dose (6-mg) naltrexone was superior to placebo for reducing pain in women with fibromyalgia in a double-blind trial at a single center in Denmark. Women ages 18 to 64 years and diagnosed with fibromyalgia were randomly assigned to naltrexone (n=49) or placebo (n=50). The primary outcome in the intention-to-treat population was change in pain intensity on an 11-point scale from baseline to week 12, with safety assessed in those who received at least one dose of the study drug. Results were published Dec. 5 by The Lancet Rheumatology.

The mean change in pain intensity was –1.3 points (95% CI, –1.7 to –0.8 points) in the naltrexone group and –0.9 (95% CI, –1.4 to –0.5 points) in the placebo group, a nonsignificant between-group difference of –0.34 point (95% CI, –0.95 to 0.27 point; P=0.27). A higher proportion of participants in the naltrexone group than in the placebo group reported a more than 30% decrease in pain (45% vs. 28%), but the researchers wrote that the study was not powered to detect a difference between groups, and the sample size was most likely too small to detect a significant difference. While there was a significant between-group difference in improving memory problems, the researchers noted that this might be a false positive due to multiplicity.

Four of 49 patients in the naltrexone group and three of 50 in the placebo group (8% vs. 6%) stopped taking their assigned drug because of intolerable side effects. Overall, adverse events were reported in 84% of the naltrexone group and 86% of the placebo group. The median number of adverse events reported per patient was three in the naltrexone group and two in the placebo group. The most frequent adverse event was headache, which occurred in 37% of the naltrexone group and 38% of the placebo group. Vivid dreams, diarrhea, constipation, increased appetite, dizziness, and hot flushes were reported more than twice as frequently in the naltrexone group than in the placebo group. Constipation and increased appetite were not common (<10%).

Although the study did not show a reduction in pain with naltrexone, the “results indicate that low-dose naltrexone might improve memory problems associated with fibromyalgia, and we suggest that future trials investigate this further,” the study authors concluded.