Low-Dose Naltrexone (LDN): Label, Studies, Tracking
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Low-Dose Naltrexone (LDN): label, studies and tracking

Strengths and studied amounts · Approval status · Half-life notes

What is Low-Dose Naltrexone?

Low-dose naltrexone (LDN) is naltrexone, an opioid blocker, taken at a few milligrams instead of the 50 mg on the FDA label. Naltrexone is approved for alcohol dependence and to block the effects of opioids; low doses are an off-label use that has been studied for chronic pain conditions such as fibromyalgia.

Also known as: LDN, naltrexone.

Strengths and studied amounts

FDA-labeled naltrexone tablets are 50 mg. We found no FDA-labeled low-dose naltrexone product on DailyMed. Fibromyalgia trials used 4.5 mg a day (Younger, 2013) and 6 mg a day (Bruun, 2024). These are trial protocols, not personalized advice; confirm any dosing with your prescriber.

Approval status and how it is used

The FDA naltrexone tablet label approves 50 mg once a day for alcohol dependence and to block the effects of opioids taken from outside the body. It warns that naltrexone can trigger sudden opioid withdrawal in anyone still dependent on opioids, so people must be opioid-free (including tramadol) for at least 7 to 10 days first. After stopping, people may respond to lower doses of opioids than before, and overdose deaths have been reported. Liver injury has also been reported. See the naltrexone side effects page for the label's numbers.

Low doses are off-label. In a small 2013 crossover trial in 31 women with fibromyalgia (Younger), 4.5 mg a day cut daily pain by 28.8% versus 18.0% on placebo. A larger 2024 trial in 99 women (Bruun, Lancet Rheumatology) found no significant difference in pain between 6 mg a day and placebo after 12 weeks. Because naltrexone blocks opioids at any dose, tell your prescriber about any opioid pain medicine.

Low-Dose Naltrexone half-life and time to peak

  • Half-lifeNot listed
  • Time to peak (Tmax)within 1 hour

The FDA naltrexone label says it is almost completely absorbed and that peak levels of naltrexone and its main active metabolite, 6-beta-naltrexol, come within one hour of a dose. The label does not give a half-life, and we could not find a published pharmacokinetic study at low doses to check one against, so we do not list one.

Numbers shown are taken from the source above. Half-life varies from person to person.

How to track Low-Dose Naltrexone in Dose Track

  1. Add Low-Dose Naltrexone as a custom compound. Start typing its name and Dose Track fills in the details from its research library for you to check, and it sits next to everything else you take.
  2. Log each dose when you take it so your history shows exactly what you took and when.
  3. Set reminders on your own schedule, whether that is daily, weekly or every few days.
  4. Your log is stored on your phone and no account is needed. Data only leaves it for features you choose, like AI answers and lab reading.

How Dose Track handles peptides · Reconstitution calculator · Half-life calculator

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Frequently asked questions

What is the half-life of Low-Dose Naltrexone?+
The FDA naltrexone label says it is almost completely absorbed and that peak levels of naltrexone and its main active metabolite, 6-beta-naltrexol, come within one hour of a dose. The label does not give a half-life, and we could not find a published pharmacokinetic study at low doses to check one against, so we do not list one.
Is low-dose naltrexone FDA approved?+
No. Naltrexone tablets are FDA approved at 50 mg a day for alcohol dependence and blocking opioids. Doses of a few milligrams are off-label, and we found no FDA-labeled low-dose product on DailyMed.
Does LDN work for fibromyalgia?+
The trials disagree. A small 2013 crossover trial (31 women, 4.5 mg a day) found more pain relief than placebo. A 2024 trial in 99 women (6 mg a day for 12 weeks) found no significant difference from placebo.
Can I track Low-Dose Naltrexone in Dose Track?+
Yes. Low-Dose Naltrexone is in Dose Track's research library, so when you add it as a custom compound its details are filled in for you to check. You can then log each dose next to your other compounds, set reminders on your own schedule, and see your history next to your lab results. Your log is stored on your phone and no account is needed. Data only leaves it for features you choose, like AI answers and lab reading.

Sources

  1. Naltrexone hydrochloride tablets 50 mg (SpecGx) prescribing information: indications, warnings, clinical pharmacology and dosage. DailyMed, September 2026.
  2. Younger J, et al. Low-dose naltrexone for the treatment of fibromyalgia: findings of a small, randomized, double-blind, placebo-controlled, counterbalanced, crossover trial. Arthritis Rheum. 2013;65(2):529-538.
  3. Due Bruun K, et al. Naltrexone 6 mg once daily versus placebo in women with fibromyalgia: a randomised, double-blind, placebo-controlled trial. Lancet Rheumatol. 2024;6(1):e31-e39.

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