By Pat Anson, PNN Editor

In recent years, low-dose naltrexone (LDN) has grown in popularity as a treatment for fibromyalgia and other chronic pain conditions. Although naltrexone is only FDA-approved for the treatment of substance use disorders, a growing number of patients and providers say low doses of naltrexone prescribed off-label can be effective in relieving pain.

A new study by Danish researchers is casting doubt on the some of those claims, finding that LDN works no better than a placebo in reducing pain for women with fibromyalgia. In their double-blind, placebo-controlled study, 99 adult women with fibromyalgia were randomly assigned to receive either an LDN pill or an identical-looking placebo daily for 12 weeks.

The study findings, recently published The Lancet Rheumatology, found a minor improvement in pain intensity for the LDN group, with a similar pain reduction in the placebo group. There were no serious adverse events in either group.

“This study did not show that treatment with low-dose naltrexone was superior to placebo in relieving pain. Our results indicate that low-dose naltrexone might improve memory problems associated with fibromyalgia, and we suggest that future trials investigate this further,” wrote lead author Karin Due Bruun, MD, a researcher in the Pain Center at Odense University Hospital in Denmark.

The Danish study is notable, because placebo-controlled, double-blind studies are considered the gold standard in medical research. Until now, much of the evidence about LDN has been anecdotal or low quality.

In a 2020 review of nearly 800 LDN studies, another research team could find only eight that were high quality enough to meet their criteria for evaluation. Nevertheless, they found that LDN “provides an alternative in medical management of chronic pain disorders.”

A 2019 review by British researchers also found that LDN is safe to use, but recommended that more clinical studies be conducted.

How naltrexone works is not exactly clear. LDN supporters believe the drug modulates the immune system, reduces inflammation and stimulates the production of endorphins, the body's natural painkiller.

In 50mg doses, naltrexone blocks opioid receptors in the brain and decreases the desire to take opiates or alcohol. But in smaller doses of 5mg or less, patients have found LDN to be an effective pain reliever. PNN columnists have shared their positive experiences using LDN to treat everything from interstitial cystitis to Ehlers-Danlos syndrome to fibromyalgia.  

A woman with fibromyalgia tried all sorts of FDA-approved medications to relieve her leg pain, brain fog and depression. None worked, until she tried LDN.   

“After about seven days, my pain lessened,” said Janice Hollander. “[LDN] has completely changed my life. I don’t know that I would be here today if it wasn’t for it. I don’t think I could go for another year in the misery I was in.” 

Naltrexone does cause minor side effects, such as nausea and dizziness, and because it is an opioid antagonist it should not be taken with opioid medication.

Patients interested in trying LDN often encounter doctors who won’t prescribe it off-label. The LDN Research Trust includes a list of LDN-friendly doctors and pharmacies on its website.