Bested 2023: low-dose naltrexone didn't ease fibromyalgia pain

What they tested

Fifty-eight people with fibromyalgia, a long-term pain condition, took low-dose naltrexone 4.5 mg or an inactive placebo once a day, then switched after a washout break. In this crossover design, each person tries both. Neither they nor the researchers knew which they were taking.

The main outcomes were the revised Fibromyalgia Impact Questionnaire (FIQR), which scores how much the condition affects daily life, and summed pain intensity ratings (SPIR). The team also tested pain processing in an experimental pain model and measured how the body handled the drug.

What they found

The median difference in FIQR scores between low-dose naltrexone and placebo was -1.65 (effect size 0.15; P = 0.3). For pain ratings, it was -0.33 (effect size 0.13; P = 0.4).

The authors concluded the results did not show any clinically relevant pain relief from low-dose naltrexone in fibromyalgia.

Limits

• Treatment periods were short (days -3 to 21 and days 33 to 56), so the trial can't speak to longer use.
• With 58 people, it could miss a small benefit.

What it means if you're considering naltrexone

Low-dose naltrexone is often tried for fibromyalgia on the strength of earlier preliminary studies. This placebo-controlled trial didn't find a meaningful benefit for pain, which weakens the case for it.