Younger 2009: low-dose naltrexone for fibromyalgia, a pilot study

What they tested

Ten women with fibromyalgia, a long-term condition with widespread muscle pain and tenderness, went through four stages: 2 weeks of baseline, 2 weeks of placebo (a dummy pill), 8 weeks of low-dose naltrexone, and 2 weeks off the drug. It was single-blind, meaning only one side, rather than both participants and researchers, was kept unaware of when the drug was given.

The women rated their symptoms every day on a handheld computer, and visited the lab every 2 weeks for tests of sensitivity to pressure, heat and cold.

What they found

Across the group, symptoms dropped by more than 30% on low-dose naltrexone compared with placebo. Lab tests showed the women tolerated more pressure and heat before feeling pain while on the drug.

Side effects, including insomnia and vivid dreams, were rare and described as minor and short-lived.

A blood test for general inflammation, the erythrocyte sedimentation rate (ESR), taken at the start, predicted over 80% of the variation in how much people responded. Women with higher ESR had the biggest drop in symptoms.

Limits

• It included only ten women, all with fibromyalgia.
• It wasn't randomized: the placebo always came before the drug, so improvement over time could be mistaken for a drug effect.
• It was single-blind rather than double-blind, which leaves more room for expectations to shape the results.

What it means if you're considering naltrexone

Low-dose naltrexone is a different use from the 50 mg tablet prescribed for alcohol or opioids. This early pilot is one of the studies that sparked interest in it for fibromyalgia, but it's small and its design is weak.

The site's guide on low-dose naltrexone notes that later, larger trials of LDN for pain did not all find a benefit, so this result shouldn't be read on its own.