Ask CLYR: Low-dose naltrexone (LDN) is naltrexone taken at a small fraction of the standard FDA-approved 50 mg tablet. It is compounded, not FDA-approved at this dose, and prescribed off-label. Research is early and mixed, so a licensed provider decides whether it is appropriate for you.
Low-dose naltrexone, usually shortened to LDN, comes up a lot in online health communities. The idea is simple to state: take a familiar, inexpensive medicine at a much smaller dose than usual, and see whether it changes how the body handles inflammation and pain signaling. The reality is more careful than the online buzz. LDN is a compounded capsule, it is not FDA-approved at this dose, and it is prescribed off-label. This guide explains what that means, how researchers think it might work, what the studies found, and how a prescription works at CLYR.
What LDN is
Naltrexone is an old, well-studied molecule. The version most pharmacies stock is the standard FDA-approved 50 mg tablet. Low-dose naltrexone uses the same molecule at a far smaller dose. Published reviews describe LDN as roughly 1 to 5 mg a day (Toljan and Vrooman, 2018). That is research background, not a menu: CLYR offers one strength, 4.5 mg, which is the low dose CLYR offers and the dose used in several published LDN trials.
Because no manufacturer makes a 4.5 mg tablet, LDN is prepared by a licensed compounding pharmacy to a provider's prescription. Compounded medicines are not FDA-approved, and the FDA has not reviewed LDN for safety or effectiveness at this dose. Using it is a decision a licensed provider makes with you, off-label. For a side-by-side look at the two products, read LDN vs the standard 50 mg tablet.
How it is thought to work
Everything in this section is a hypothesis. Researchers are still testing these ideas, and none of them has been proven to produce a benefit in people.
A brief nightly block, then clearance
At a low dose, naltrexone is thought to block the receptor it targets for only a few hours before the body clears it. One proposal is that this short block, often taken at bedtime, prompts the body to adjust its own endorphin signaling over the following hours. Reviews describe this as a working theory that still needs testing (Toljan and Vrooman, 2018; Younger and colleagues, 2014).
Immune cells in the nervous system
A second hypothesis involves glial cells, the support and immune cells of the brain and spinal cord. Naltrexone may interact with a receptor on these cells called TLR4, which is involved in inflammatory signaling. Much of the support for this idea comes from lab work. For example, Kučić and colleagues (2021) studied naltrexone in lab-grown microglial cells, which tells us about cells in a dish, not about people.
What it has been studied for
LDN has been studied in small trials across several conditions. The table below summarizes the evidence grade we assigned after reading the studies, with a link to a full write-up for each.
| Condition | Evidence so far | Read more |
|---|---|---|
| Long COVID | Very low: no randomized trial results yet | LDN and long COVID |
| Fibromyalgia | Mixed: early small trials positive, the largest recent trials negative | LDN and fibromyalgia |
| Hashimoto's | None: no clinical trials found | LDN and Hashimoto's |
| Multiple sclerosis | Low and mixed: small, short trials | LDN and multiple sclerosis |
Broader reviews reach a similar conclusion. Patten and colleagues (2018) reviewed safety and efficacy data and found the studies small, and a 2025 scoping review by Leiber and colleagues mapped many proposed uses, most supported by limited evidence.
What the evidence does not show
No condition has strong, consistent support from large randomized trials. Fibromyalgia is the clearest example. Early small studies were encouraging, but two larger placebo-controlled trials were not. In a 2024 trial of 99 women by Due Bruun and colleagues, 6 mg a day did not beat placebo for pain. In a 12-month trial published in 2026 by Rodríguez-Freire and colleagues, 4.5 mg did not show a clinically meaningful benefit over placebo. Any honest description of LDN has to include those results.
Who prescribes it and how
LDN needs a prescription. At CLYR, you complete an online health screening, and a licensed provider reviews your history and every medicine you take before deciding whether LDN is appropriate. If it is prescribed, a state-licensed 503A compounding pharmacy prepares the 4.5 mg capsules, and they ship to most states and Puerto Rico. Your provider writes the directions, typically one capsule nightly or as your provider directs. The steps are in how to get LDN online, and the dose itself is covered in LDN dosing: why 4.5 mg.
Safety basics
In trials, LDN side effects were usually mild. Vivid dreams, sleep changes and nausea came up most often. A 2019 meta-analysis of placebo-controlled trials of oral naltrexone across many uses found no increase in serious adverse events (Bolton and colleagues). Some health conditions and medicines rule LDN out, which is why screening comes first. The details are in LDN side effects: what the studies reported and in the safety section below.
Cost at CLYR
At CLYR, low-dose naltrexone 4.5 mg is $119 for 30 capsules or $169 for 90 capsules. Each order is billed once and nothing renews. Provider review and shipping are included, and your provider sets the days of supply. Insurance rarely covers compounded LDN, and CLYR is cash-pay. See what LDN costs and how to compare prices, or go straight to low-dose naltrexone 4.5 mg at CLYR.
Frequently asked questions
Is LDN FDA-approved?
No. Naltrexone is FDA-approved as the standard 50 mg tablet. Low-dose naltrexone is a compounded capsule prescribed off-label, and the FDA has not reviewed it for safety or effectiveness at this dose.
What dose does CLYR offer?
CLYR offers one strength, 4.5 mg capsules. It is the low dose CLYR offers, and your provider decides whether it is appropriate for you and writes the directions.
How is LDN thought to work?
Researchers think a brief nightly receptor block and effects on immune cells in the nervous system may play a role. These are hypotheses that are still being tested.
What has LDN been studied for?
Small studies have looked at fibromyalgia, multiple sclerosis, long COVID and other conditions. Results are mixed, and the largest recent fibromyalgia trials did not show a benefit over placebo.
Do I need a prescription?
Yes. LDN needs a prescription from a licensed provider, who reviews your health history and medicines first.
Important safety information
Compounded low-dose naltrexone is a prescription capsule dispensed only after a licensed provider independently reviews your intake and determines it is appropriate for you. Do not take naltrexone if you take any opioid medicine or have taken one in the last 14 days, including tramadol, codeine, methadone or buprenorphine, because naltrexone blocks them and can cause sudden withdrawal; do not take it if you currently take or need opioid medicines, have liver disease, hepatitis or abnormal liver tests, or are allergic to naltrexone. Tell your provider about kidney disease, pregnancy, breastfeeding or plans for pregnancy, and about every medication and supplement you take. Side effects may include vivid dreams, trouble sleeping, headache, nausea, dizziness or anxiety. Carry a note that you take naltrexone, because opioid pain medicines may not work normally while it is in your system. Compounded medications are made by a licensed U.S. 503A pharmacy to a provider's prescription; they are not FDA-approved and have not been reviewed by the FDA for safety or effectiveness. Individual results vary. Not everyone qualifies. This page is informational and is not medical advice. Call 911 in an emergency.
The same text appears in the Important Safety Information on the LDN page.