Low-dose naltrexone for fibromyalgia is not standard of care


This week I saw an interesting tweet about low-dose naltrexone for fibromyalgia purporting that this therapy is “standard of care.” I’m not that surprised since I’m asked about it now and then. Google “fibromyalgia and low-dose naltrexone” and the Internet is awash with efficacy claims. Even Medscape, a physician education portal, has a post from 2012 entitled, “Confirmation: Low-dose naltrexone eases fibromyalgia pain.”


That is not what the *cough* body of literature says. Not at all. Actually, to be honest there isn’t even analtrexone body of literature there are two clinical trials looking at low-dose naltrexone and fibromyalgia (both from the same researcher). One is a single-blind cross-over study comparing 4.5 mg of naltrexone with placebo completed by 10 patients and the other is a double-blinded cross-over trial of the same dose completed by 28 patients.

In both studies there was about a 32% response rate meaning about one-third of the patients taking low-dose naltrexone felt improved. Interestingly, in these studies the placebo response rates were 11% and 18%, which is much lower than expected. In a recent double-blinded study of pregabalin for fibromyalgia the placebo response rate was 27%, far more typical for fibromyalgia studies.

The 32% response rate of the two low-dose naltrexone studies does look less impressive when compared against a more typical placebo response rate of 27%.

What can we learn from this?

Two studies with a total of 38 patients does not make a therapy standard of care, it makes it highly experimental. Given the low placebo response rate in the studies there are definite questions regarding the methodology or the possibility that naltrexone has side effects that make blinding a challenge. Or both.

There are some potentially interesting ideas behind naltrexone for fibromyalgia, but there are lots of interesting ideas that simply don’t hold up to the scientific method. That is, of course, why we need more than 2 small studies with possible flaws to say that any treatment is worth while trying, never mind saying that is the standard of care. And sites like Medscape, that are read by physicians and patients alike, should be more careful about headlines that spout “proof” based on such a paucity of data.


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