The dose the trials used
Three of the most cited studies converge on one number. The randomized, double-blind, placebo-controlled crossover trial in 31 women with fibromyalgia gave 4.5 mg of oral naltrexone daily and reported a 28.8% reduction in baseline pain on LDN against 18.0% on placebo, with 32% of participants meeting a response definition on LDN against 11% on placebo; participants rated it as tolerable as placebo and no serious side effects were reported. The open-label pilot in active Crohn’s disease used 4.5 mg a day, with patients’ other Crohn’s therapy continued at stable doses. The eight-week crossover pilot in multiple sclerosis used 4.5 mg nightly. The follow-up fibromyalgia study that measured inflammatory cytokines ran eight weeks of LDN inside a ten-week crossover. When a clinician talks about “the LDN dose”, 4.5 mg is the number the evidence sits on. What those studies found is in the LDN benefits guide.
Why the range is 1 to 5 mg
The 2018 review of the therapeutic literature defines low-dose naltrexone as a daily dose of 1 to 5 mg and separates it from two other ranges: very-low-dose naltrexone, 1 microgram to 1 mg, used experimentally alongside opioid tapers, and ultra-low-dose, lower still. The distinction matters because the proposed mechanism depends on the dose: at 1 to 5 mg, naltrexone briefly and partially blocks opioid receptors, which appears to raise the body’s own endorphin signaling, and it modulates Toll-like receptor 4 on glial cells, which is the anti-inflammatory arm. At 50 mg it fully blocks opioid receptors around the clock, which is a different drug in effect. Nothing about the low-dose evidence transfers to higher doses.
How clinicians step up to it
The trials started patients at 4.5 mg. In practice many clinicians begin lower, commonly around 1.5 mg, and raise the dose in steps toward 4.5 mg over several weeks, because the most common early side effects, vivid dreams and disturbed sleep, tend to ease as the dose settles and are easier to manage from a lower start. That ladder is clinical practice, not a trial protocol, and the clinician who prescribes your LDN decides both the starting point and the pace. Because the capsule is compounded to the strength written, each step is a new strength from the pharmacy, not a split tablet.
When to take it
The multiple sclerosis pilot dosed at night, and nightly dosing is common practice, on the reasoning that the brief receptor blockade overlaps sleep. Some people find the vivid dreams easier to tolerate with morning dosing instead. Timing is a conversation with your clinician rather than a rule; what matters more is taking it at a consistent time each day.
How long before it works
The trials measured effects over eight to twelve weeks. The fibromyalgia crossover assessed daily pain across the active phase, the cytokine study measured markers after eight weeks, and the MS pilot ran eight weeks per arm. A fair trial of LDN is therefore a matter of weeks at the target dose, judged with the clinician by symptoms and, where relevant, labs. Side effects reported in the trials were mild; the fibromyalgia trial rated tolerability equal to placebo.
The rule that does not move with the dose
Naltrexone blocks opioid receptors, so low-dose naltrexone cannot be combined with opioid medications, including some pain and cough prescriptions, at any dose in the range. Taken alongside a regular opioid it blocks the opioid’s effect and can trigger withdrawal. Tell the clinician about every prescription before LDN is considered.
Getting the dose prescribed
Low-dose naltrexone is prescription-only and compounded. At PepScribe the online visit is free, a US-licensed clinician decides whether LDN fits your history and sets the dose, and if prescribed, a licensed 503A pharmacy compounds the capsule to that strength and ships it, with the medication, the clinical care and shipping inside one flat monthly plan. Every dose is compounded in the USA by licensed 503A pharmacies. No hidden overseas supply chain. The how to get LDN online guide walks the path step by step, and the LDN treatment page describes PepScribe’s approach.
Frequently asked questions
What is the standard dose of low-dose naltrexone?
The published trials used 4.5 mg once daily, and a 2018 review defines LDN as 1 to 5 mg a day. Your clinician sets your dose within that range.
Do you start LDN at 4.5 mg?
The trials did. Many clinicians start lower, often around 1.5 mg, and step up toward 4.5 mg over several weeks to manage sleep effects and vivid dreams. That is clinical practice, and the prescribing clinician decides the pace.
Should low-dose naltrexone be taken at night?
The MS pilot dosed nightly and that is common practice; some people tolerate morning dosing better. Take it at a consistent time and settle the timing with your clinician.
How long does low-dose naltrexone take to work?
The trials measured effects over eight to twelve weeks. Expect a trial of weeks at the target dose, judged with your clinician.
Can I take a higher dose for a stronger effect?
The low-dose evidence covers 1 to 5 mg. Above that range naltrexone behaves differently, blocking opioid receptors fully, and none of the low-dose findings apply. The dose is the clinician's decision.
What are the side effects at these doses?
The most commonly reported are vivid dreams, disturbed sleep, headache and nausea, usually mild; the fibromyalgia trial rated LDN as tolerable as placebo with no serious side effects. It must never be combined with opioid medications.
