Low-dose naltrexone: what the trials found when they got bigger
Low-dose naltrexone has an unusually clean evidence story, and it doesn't end where its marketing does. A small Stanford crossover trial in 2013 found a real effect on fibromyalgia pain and asked for larger parallel-group trials. Those trials were run. The 2024 one in The Lancet Rheumatology found no difference from placebo.
What this comes down to
- Naltrexone is approved at 50 mg for alcohol dependence and opioid blockade. Low-dose naltrexone means roughly 1.5 to 4.5 mg, which no approved single-ingredient product supplies.
- Our September 2026 PubMed search found 37 trial-tagged low-dose naltrexone reports, none matching its weight-loss or obesity terms.
- The 2013 crossover trial in 31 women found 28.8% pain reduction against 18.0% on placebo. The 2024 trial in 99 women found a between-group difference of 0.34 points on an 11-point scale, p=0.27.
- Naltrexone is a component of approved products, so a compounder has a lawful route to it. Here the legal question isn't the hard one; the evidence question is.
- All trial-tagged reports37
- About weight0
What the approved drug is, and what low-dose means
Naltrexone hydrochloride is an opioid antagonist approved in tablets at 25, 50 and 100 mg, indicated for alcohol dependence and for blocking the effects of opioids[1]. Only one other approved product carries a small amount of it: Contrave, at 8 mg of naltrexone with 90 mg of bupropion, approved for weight management in 2014[2].
Low-dose naltrexone means something well below all of those — usually 1.5 to 4.5 mg, taken daily, compounded because there isn't an approved product at that strength. The theory is that a brief, partial opioid blockade produces a rebound effect and damps neuroinflammation. It's a plausible mechanism, and it's carrying a thin outcome record.
The trials, in the order they happened
In 2013 a Stanford group published a counterbalanced crossover trial in 31 women with fibromyalgia. Daily pain fell 28.8% on 4.5 mg of naltrexone against 18.0% on placebo, p=0.016, with a 32% response rate against 11%[3]. The authors closed by saying parallel-group randomized trials were needed to determine efficacy.
Eleven years later, one arrived. A Danish single-center trial randomized 99 women to 6 mg of low-dose naltrexone or an identical placebo for twelve weeks. Pain fell 1.3 points on the drug and 0.9 on placebo — a between-group difference of 0.34 points on an 11-point scale, p=0.27[4]. The paper's own conclusion is that it didn't show superiority over placebo.
A small crossover trial hints at something. Its authors say so and ask for a bigger one. The bigger one comes back null. Neither result was hidden and neither investigator did anything wrong. The finding is simply that the effect didn't survive a stronger design.
The weight-loss search found no trial-tagged reports
This is the reason people find it on a GLP-1 platform, so it's worth being exact. Filtered to randomized trials in humans, PubMed holds 37 papers on low-dose naltrexone. Add any weight term to the same query and the count is zero. The filter isn't broken: the identical filter finds seven trial-tagged fibromyalgia reports and 312 trial-tagged semaglutide reports.
The search behind that zero. A PubMed search finds 0 results; the same search for low-dose naltrexone in fibromyalgia finds 7.
The approved weight product pairs 8 mg of naltrexone with 90 mg of bupropion, and the trials behind it tested that combination. Nothing in that record transfers to 4.5 mg of naltrexone on its own.
The legal position is the easy part
Naltrexone hydrochloride is the active ingredient of approved drug products, which satisfies the second of the three conditions a 503A compounder needs[5]. It's absent from the FDA's page of substances flagged as presenting significant safety risks in compounding[6]. Compounding it at 4.5 mg is a routine pharmacy operation — which is exactly why the interesting question here is the evidence one, not the legality one, unlike most peptides on these menus.
What it costs where we have found it
| Seller | What it is called | A month |
|---|---|---|
| Nurx | bupropion and naltrexone (brand) | $60 |
| WePeptideRx | low dose naltrexone (compounded) | $79 |
| Tyde Wellness | low-dose naltrexone tablets, published floor (compounded) | $119 |
| NEUVÉ Health | low dose naltrexone, monthly program fee (compounded) | $137 |
Naltrexone lines on the sellers we review
Two different things sit in that table. One is the approved bupropion and naltrexone combination; the other is a compounded low-dose preparation with no approved equivalent. A price list rarely distinguishes them, and our reviews name which is which.
Questions people actually ask
Does low-dose naltrexone help with weight loss?
Our September 2026 search found no randomized-trial reports testing it for that. PubMed holds 37 trial-tagged reports of low-dose naltrexone and none of them uses a weight or obesity term, while the identical filter finds seven trial-tagged fibromyalgia reports. The approved weight product containing naltrexone pairs it with bupropion at a different dose.
Is low-dose naltrexone FDA approved?
Not at that dose. Naltrexone is approved as 25, 50 and 100 mg tablets for alcohol dependence and opioid blockade, and as an 8 mg component of a combination weight product. A 4.5 mg single-ingredient preparation has to be compounded, and compounded drugs aren't FDA reviewed before sale.
Why did the newer fibromyalgia trial disagree with the older one?
Design and size. The 2013 result came from a 31-person crossover trial whose own authors asked for larger parallel-group work. The 2024 trial was that work: 99 women, twelve weeks, double-blind, parallel groups. It found a 0.34-point difference on an 11-point pain scale, which wasn't statistically significant.
Can you take low-dose naltrexone with opioid painkillers?
Naltrexone is an opioid antagonist, and the approved label warns about precipitated withdrawal in anyone dependent on opioids, recommending an opioid-free interval of at least seven to ten days before starting. This is a question for a prescriber who knows your full medication list.
Sources
Every source below was read for this article, with the claim it supports written beside it.
- 1.Naltrexone hydrochloride tablets — FDA prescribing information. U.S. Food and Drug Administration, Structured Product Labeling, 2023. Source · Document dated December 2023; read September 2026The approved indication — treatment of alcohol dependence and blockade of the effects of exogenously administered opioids — and the warning on precipitated withdrawal with a recommended opioid-free interval of seven to ten days.
- 2.Drugs@FDA: FDA-Approved Drugs, queried through the openFDA API. U.S. Food and Drug Administration, 2026. Source · Read September 2026Naltrexone hydrochloride resolves to twelve applications. The single-ingredient oral products are 25, 50 and 100 mg tablets; the only currently marketed product carrying a smaller amount is Contrave, NDA 200063, approved September 10, 2014, at 8 mg naltrexone with 90 mg bupropion.
- 3.Low-dose naltrexone for the treatment of fibromyalgia: findings of a small, randomized, double-blind, placebo-controlled, counterbalanced, crossover trial assessing daily pain levels. Arthritis & Rheumatism, 2013. PMID 23359310 · doi:10.1002/art.37734 · Read September 2026Thirty-one women, 4.5 mg daily, crossover design: 28.8% pain reduction against 18.0% on placebo (p=0.016), a 32% response rate against 11% (p=0.05), and the authors' own call for parallel-group randomized trials.
- 4.Naltrexone 6 mg once daily versus placebo in women with fibromyalgia: a randomised, double-blind, placebo-controlled trial. The Lancet Rheumatology, 2024. PMID 38258677 · doi:10.1016/S2665-9913(23)00278-3 · Read September 2026Ninety-nine women randomized, twelve weeks: pain fell 1.3 points on low-dose naltrexone and 0.9 on placebo, a between-group difference of 0.34 points (95% CI −0.95 to 0.27, p=0.27), and the trial did not show superiority over placebo.
- 5.Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act. U.S. Food and Drug Administration, 2026. Source · Document dated May 2026; read September 2026The three conditions a bulk substance must meet under section 503A, of which naltrexone hydrochloride meets the second: it is a component of FDA-approved drug products.
- 6.Substances in Compounding that May Present Significant Safety Risks. U.S. Food and Drug Administration, 2026. Source · Document dated April 2026; read September 2026Naltrexone appears nowhere on the category-2 page, on either table, although the same page lists ipamorelin six times.
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