Fibromyalgia Symptoms Are Reduced by Low-Dose Naltrexone: A Pilot Study.

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Pain Med. 2009 Apr 22.
Fibromyalgia Symptoms Are Reduced by Low-Dose Naltrexone: A Pilot Study.Younger J, Mackey S.School of Medicine, Department of Anesthesia, Division of Pain Management, Stanford University, Palo Alto, California, USA.Objective.
Fibromyalgia is a chronic pain disorder that is characterized by
diffuse musculoskeletal pain and sensitivity to mechanical stimulation.
In this pilot clinical trial, we tested the effectiveness of low-dose
naltrexone in treating the symptoms of fibromyalgia.
Design.
Participants completed a single-blind, crossover trial with the
following time line: baseline (2 weeks), placebo (2 weeks), drug (8
weeks), and washout (2 weeks).
Patients. Ten women meeting criteria for
fibromyalgia and not taking an opioid medication. Interventions.
Naltrexone, in addition to antagonizing opioid receptors on neurons,
also inhibits microglia activity in the central nervous system. At low
doses (4.5 mg), naltrexone may inhibit the activity of microglia and
reverse central and peripheral inflammation. Outcome Measures.
Participants completed reports of symptom severity everyday, using a
handheld computer. In addition, participants visited the lab every 2
weeks for tests of mechanical, heat, and cold pain sensitivity.
Results. Low-dose naltrexone reduced fibromyalgia symptoms in the
entire cohort, with a greater than 30% reduction of symptoms over
placebo. In addition, laboratory visits showed that mechanical and heat
pain thresholds were improved by the drug. Side effects (including
insomnia and vivid dreams) were rare, and described as minor and
transient. Baseline erythrocyte sedimentation rate predicted over 80%
of the variance in drug response. Individuals with higher sedimentation
rates (indicating general inflammatory processes) had the greatest
reduction of symptoms in response to low-dose naltrexone.
Conclusions.
We conclude that low-dose naltrexone may be an effective, highly
tolerable, and inexpensive treatment for fibromyalgia.