Low-Dose Naltrexone FDA Approval History: What Patients and Prescribers Need to Know
Oral naltrexone was first approved in 1984, and its alcohol-dependence indication followed in 1994. Those approvals concern standard-dose treatment, not low-dose naltrexone for fibromyalgia, Crohn's disease or multiple sclerosis. LDN refers to a lower-dose prescribing approach using the same active ingredient. [1,2]
For someone researching a prescription, three details make the history easier to understand: the exact formulation, the condition being treated and the dose studied for that condition.
The approval timeline
| Date | Product or change | What it established |
|---|---|---|
| November 20, 1984 | Oral naltrexone, originally Trexan | Approval for blocking the effects of externally administered opioids [1] |
| 1994 | Alcohol-dependence indication; ReVia branding | A further approved use of oral naltrexone [2] |
| April 13, 2006 | Vivitrol extended-release injection | Monthly injectable naltrexone for alcohol dependence [3] |
| October 12, 2010 | Vivitrol supplemental approval | Prevention of relapse to opioid dependence after detoxification [3] |
The current 50 mg oral-tablet label lists alcohol dependence and blockade of opioid effects as its indications, within a broader treatment plan. Vivitrol is a separate long-acting injectable product. Neither formulation's approval establishes an LDN indication for the conditions above. [3,4]
What makes a prescription “low dose”?
LDN is a clinical description, not a separate FDA-approved brand or a single standardized regimen. Studies have used different amounts: 4.5 mg daily in several fibromyalgia trials and 6 mg daily in another. The dose should therefore be tied to a specific treatment plan rather than inferred from the letters LDN. [5,6,7]
FDA describes off-label prescribing as using an approved medicine for a different condition, dose or route when the clinician judges that appropriate. A compounded low-strength capsule or liquid is also a distinct preparation: the finished compounded product does not receive the same premarket approval as a manufactured drug product. [8,9]
What has actually been studied?
Fibromyalgia
A 2013 crossover trial enrolled 31 women and compared 4.5 mg naltrexone with placebo. Pain reduction from baseline was 28.8% during naltrexone treatment versus 18.0% during placebo treatment. [5]
Later trials provide a fuller picture. A 2024 study randomized 99 women to 6 mg daily or placebo for 12 weeks. Average pain improvement was 1.3 points with naltrexone and 0.9 points with placebo on a 0-to-10 scale; the between-group difference was not statistically significant. [6]
The 2026 INNOVA trial randomized 98 women to 4.5 mg daily or placebo as add-on treatment and followed outcomes for 12 months. Its primary three-month pain outcome did not show a clinically meaningful advantage for naltrexone. [7]
These are treatment results for defined doses and populations. When discussing LDN for fibromyalgia, use the later trials alongside the earlier positive study and agree on which symptoms and functions will determine whether continuing treatment is worthwhile.
Crohn's disease
A 2013 pediatric pilot enrolled 14 children aged 8 to 17. It compared naltrexone with placebo for eight weeks, followed by an open-label naltrexone phase. The study primarily examined safety and tolerability; disease-activity scores improved relative to pretreatment values. That is different from demonstrating a definitive placebo-controlled remission benefit. [10]
Multiple sclerosis
A 2010 crossover trial enrolled 80 people, with 60 completing the study. It examined eight weeks of 4.5 mg nightly naltrexone and found improvements in several mental-health quality-of-life measures. The reported outcomes were patient-reported quality of life, not proof of reduced MRI lesions or prevention of disability progression. [11]
How a low-strength prescription is filled
Compounding allows a pharmacy to prepare a formulation for a particular patient when appropriate. Ask the dispensing pharmacist to confirm the strength per capsule or per milliliter, the measuring device for a liquid, storage instructions and the beyond-use date. The pharmacy should be able to explain exactly what was prepared and how it should be used. [9]
Keep that label with your medication list. “Naltrexone” alone does not distinguish a low-strength capsule from a 50 mg tablet or a monthly injection. If the pharmacy changes the formulation or concentration, check the new directions rather than carrying over an old volume or tablet-splitting routine.
What the current liver warning says
The current oral-tablet label includes a hepatotoxicity warning, but it is not presented as a boxed warning in the reviewed labeling. It reports hepatitis and clinically significant liver dysfunction during development and postmarketing use. A low-dose prescription still needs a review of liver history and other medicines. [4]
Contact the prescribing team promptly for yellow skin or eyes, dark urine, right-upper-abdominal pain or other symptoms suggesting a liver problem. The label advises discontinuing naltrexone when symptoms or signs of acute hepatitis occur. [4]
Opioid medicines need a separate review
Naltrexone blocks opioid receptors and can precipitate withdrawal in someone who is opioid-dependent. Tell the prescriber about opioid pain medicines, methadone or buprenorphine before starting. They need to determine an appropriate opioid-free interval; the usual tablet-label interval for short-acting opioids is at least seven to ten days, with longer vulnerability after methadone or buprenorphine. [4]
Keep other treating clinicians informed that you take naltrexone, particularly when discussing pain treatment. A low-strength prescription should not be used as a reason to skip that medication review.
Does an expired patent explain the approval status?
Patent status and FDA marketing exclusivity are different. FDA describes several forms of exclusivity, including three-year exclusivity for qualifying new clinical investigations. A medicine's generic status does not establish that every new formulation or indication would be immediately open to competitors. [12]
For a treatment decision, focus on the proposed dose, the clinical goal and the studies relevant to that goal. Ask when symptoms will be reassessed and what would lead the prescriber to continue, adjust or stop the treatment.
References
- FDA. Naltrexone hydrochloride generic application records, documenting ReVia NDA 018932 approval on November 20, 1984.
- FDA. Vivitrol medical review, describing the 1984 oral approval and 1994 alcohol-dependence supplement.
- FDA. Vivitrol supplemental approval letter, October 12, 2010, also documenting the April 13, 2006 original approval.
- DailyMed. Naltrexone hydrochloride 50 mg tablets: prescribing information.
- Younger J et al. Low-dose naltrexone for fibromyalgia: randomized crossover trial. Arthritis & Rheumatism, 2013.
- Due Bruun K et al. Naltrexone 6 mg once daily versus placebo in women with fibromyalgia. Lancet Rheumatology, 2024.
- Rodríguez-Freire C et al. Efficacy of low-dose naltrexone in women with fibromyalgia: INNOVA trial. European Journal of Pain, 2026.
- FDA. Understanding Unapproved Use of Approved Drugs: Off Label.
- FDA. Understanding the Risks of Compounded Drugs.
- Smith JP et al. Safety and tolerability of low-dose naltrexone in children with Crohn's disease: pilot study. Journal of Clinical Gastroenterology, 2013.
- Cree BA et al. Pilot trial of low-dose naltrexone and quality of life in multiple sclerosis. Annals of Neurology, 2010.
- FDA. Frequently Asked Questions on Patents and Exclusivity.