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.
- Thirty-seven randomized trials of low-dose naltrexone appear in PubMed. None of them is about weight loss or obesity.
- 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.
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.
There is no weight-loss trial of low-dose naltrexone
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 fibromyalgia trials and 312 semaglutide trials.
PubMed, via the E-utilities API
("low dose naltrexone"[tiab] OR "low-dose naltrexone"[tiab]) AND (obesity[tiab] OR "weight loss"[tiab] OR "body weight"[tiab]) AND "randomized controlled trial"[pt] AND "humans"[mh]Returned 0. Positive control — low-dose naltrexone in fibromyalgia, identical filter — returned 7 through the identical filter in the same session.
The control is deliberately the same drug rather than a different one: it proves the filter can find low-dose naltrexone trials, which is the only thing that makes the zero mean anything. Unfiltered, the drug returns 379 records and 37 randomized trials. Semaglutide through the identical trial filter returns 312.
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 |
Naltrexone lines on the sellers we have read first-hand
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?
No randomized trial has tested it for that. PubMed holds 37 randomized trials of low-dose naltrexone and none of them uses a weight or obesity term, while the identical filter finds seven fibromyalgia trials. 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 here was fetched and read for this article, with the identifier taken off the record that came back and the claim it supports written down beside it. All of it was read in September 2026, the same session the rest of this page draws on.
- Naltrexone hydrochloride tablets — FDA prescribing information. U.S. Food and Drug Administration, Structured Product Labeling, 2023. Source · Document dated December 2023The 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.
- Drugs@FDA: FDA-Approved Drugs, queried through the openFDA API. U.S. Food and Drug Administration, 2026. Source · Naltrexone 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.
- 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 · Thirty-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.
- 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 · Ninety-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.
- 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 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.
- Substances in Compounding that May Present Significant Safety Risks. U.S. Food and Drug Administration, 2026. Source · Document dated April 2026Naltrexone appears nowhere on the category-2 page, on either table, while ipamorelin appears six times on the same read.