Due Bruun 2024: low-dose naltrexone vs placebo for fibromyalgia pain

What they tested

Researchers in Denmark randomly assigned 99 women with fibromyalgia, a long-term condition of widespread pain, to low-dose naltrexone 6 mg a day (49 women) or an identical-looking placebo (50 women) for 12 weeks. Participants, investigators, outcome assessors and statisticians were all kept unaware of who got which.

The main outcome was the change in pain intensity on an 11-point rating scale from the start to week 12. The trial was paid for by the Danish Rheumatism Association, Odense University Hospital and two foundations, not a drug company.

What they found

Pain went down by 1.3 points on average with low-dose naltrexone (95% confidence interval -1.7 to -0.8) and by 0.9 points with placebo. The gap of 0.34 points was small and could have been due to chance (p=0.27).

No one was lost to follow-up. Four of 49 women (8%) on low-dose naltrexone and 3 of 50 (6%) on placebo stopped because of side effects. Any adverse event was reported by 41 of 49 (84%) on naltrexone and 43 of 50 (86%) on placebo. One serious adverse event happened, in the placebo group, and no one died.

The authors noted that low-dose naltrexone might improve the memory problems linked to fibromyalgia and suggested future trials look at this. That was not the trial's main question.

Limits

• Everyone was a woman, and 98 of the 99 were White, so it says little about men or other groups.
• It ran for 12 weeks at a single centre.
• The possible memory benefit came from secondary results and would need its own trial to confirm.

What it means if you're considering naltrexone

Low-dose naltrexone is used for fibromyalgia despite little evidence, the authors note, and this was one of the larger placebo-controlled tests of it. It found no clear pain benefit. Low-dose naltrexone is also a separate use from the standard tablet for alcohol, and this trial says nothing about drinking.