Low-Dose Naltrexone (LDN) for Fibromyalgia: What Does the Research Show?

Fibromyalgia is a chronic condition characterized by widespread pain, fatigue, unrefreshing sleep, and cognitive difficulties often called “fibro fog.” Low-dose naltrexone (LDN) has attracted interest as a potential treatment because of its proposed effects on pain processing and immune signaling.

Although early clinical studies reported encouraging results, more recent randomized trials have produced mixed findings. Here is an overview of the human research.

What Is Low-Dose Naltrexone?

Naltrexone is an FDA-approved medication used at standard doses to treat alcohol use disorder and prevent opioid relapse. Low-dose naltrexone generally refers to doses of approximately 0.5–4.5 mg daily. Its use for fibromyalgia is off-label.

Researchers have proposed that LDN may influence microglia, immune signaling, and the nervous system's regulation of pain. These mechanisms remain under investigation, and their clinical significance in fibromyalgia is not fully established.

What Do Human Clinical Studies Show?

Early Studies Reporting Potential Benefits

1. Younger and Mackey, 2009 — Pilot Study

In this small study of 10 women with fibromyalgia, 4.5 mg of LDN daily was associated with a reduction in symptom severity compared with placebo. The findings suggested potential improvements in pain sensitivity and overall symptoms.

2. Younger et al., 2013 — Randomized, Double-Blind Trial

This crossover trial included 31 women with fibromyalgia. Pain decreased by 28.8% during LDN treatment compared with 18% during placebo treatment. Some measures of mood and life satisfaction also improved, although fatigue and sleep did not significantly improve.

3. Ramanathan et al., 2012 — Human Case Report

This publication described a patient with fibromyalgia and explored the hypothesis that LDN might influence endogenous opioid signaling. A case report can generate hypotheses but cannot establish treatment effectiveness.

4. Parkitny and Younger, 2017 — Immune and Symptom Study

In a 10-week pilot study involving eight women, researchers observed reductions in several circulating inflammatory cytokines after eight weeks of LDN. Participants also reported a 15% reduction in pain and an 18% reduction in overall symptoms.

These findings provided preliminary evidence for possible immune-modulating effects, but the small study and its design limit conclusions about causation.

5. Metyas et al., 2013 — Prospective, Open-Label Study

A small study of 25 patients evaluated LDN starting at 3 mg nightly, with titration up to 4.5 mg. Among the 22 participants who completed the study, the overall Revised Fibromyalgia Impact Questionnaire score improved by approximately 19.5% after three months. Half experienced an average improvement of 41%.

Because there was no placebo group, the findings cannot distinguish medication effects from placebo responses or other influences.

More Recent Randomized Trials

6. Bested et al., 2023 — Randomized, Placebo-Controlled Trial

This crossover trial included 58 patients receiving 4.5 mg of LDN or placebo. Researchers found no statistically significant difference between treatments in their primary measures of pain and fibromyalgia impact.

7. Bruun et al., 2024 — Larger Placebo-Controlled Trial

In this trial, 99 women received 6 mg of naltrexone daily or placebo for 12 weeks. The difference in pain reduction between groups was not statistically significant.

8. Rodríguez-Freire et al., 2026 — INNOVA Trial

This 12-month randomized trial included 98 women receiving 4.5 mg of LDN daily or placebo. LDN did not demonstrate a clinically meaningful advantage over placebo for pain or key secondary outcomes. The medication was generally well tolerated.

This newer study adds important longer-term evidence and reinforces the uncertainty surrounding LDN's effectiveness for fibromyalgia.

What Do Systematic Reviews Conclude?

Two recent systematic reviews reached somewhat different conclusions:

• Vatvani et al., 2024: A meta-analysis of four randomized trials involving 222 patients found a statistically significant improvement in pain scores with LDN, but no significant improvement in overall fibromyalgia impact or pain catastrophizing.
• Ologunowa et al., 2025: An analysis of eight clinical trials found that improvements from baseline were not significantly greater than placebo in pooled comparisons of pain or symptom severity.

Differences in study selection, methods, and outcome measures may help explain the conflicting findings. Overall, the evidence remains inconclusive.

Safety and Clinical Considerations

LDN is not FDA-approved for fibromyalgia, and an optimal dosing protocol has not been established. Potential adverse effects include vivid dreams, sleep disturbances, headaches, and nausea.

Naltrexone can interfere with opioid medications and may precipitate withdrawal in people who are physically dependent on opioids. Patients taking opioid pain medications, tramadol, methadone, or buprenorphine should consult their prescribing clinician before considering LDN. Liver health and other medications should also be reviewed.

For patients considering a trial, a clinician should establish treatment goals and monitor changes in pain, sleep, fatigue, daily function, and side effects.

The Bottom Line

LDN remains an interesting off-label option for fibromyalgia, supported by several small human studies reporting improvements in pain and symptoms. However, more recent and larger randomized trials—including the 2026 INNOVA study—have not demonstrated clinically meaningful benefits over placebo.

Some patients may wish to discuss a supervised trial with their healthcare provider, particularly when symptoms remain difficult to manage. Treatment decisions should reflect the mixed evidence, individual circumstances, and available alternatives.

At Valley Integrative Health , we believe in evaluating emerging therapies alongside established research and developing individualized care plans that reflect each patient's needs.

This article is for educational purposes only and does not replace individualized medical advice. LDN use for fibromyalgia is off-label.