Low-dose naltrexone (LDN): hope, studies and limits

Healthy state

Naltrexone blocks the docking sites for opioids, that is, for painkillers such as morphine and for the body’s own endorphins. At the usual dose it is used against alcohol and opioid dependence. “Low dose” means about a tenth of that.

The idea behind the low dose: naltrexone blocks the receptors only for a few hours. Afterwards, the assumption goes, the body responds with more of its own endorphins, a “rebound effect”. In addition, naltrexone inhibits a receptor (Toll-like receptor 4) on microglia, the brain’s immune cells. If these are overactive, they can promote pain sensitivity, fatigue, sleep problems and difficulty concentrating. Both are hypotheses from laboratory and animal work; in humans the chain of effects is not proven.

There are also opioid receptors in the gut, in the muscle, in the nerve plexuses of the gut wall and on immune cells. Through them, the body’s own endorphins and opioid medications slow gut movement, regulate fluid release by the lining and influence inflammation. That is why opioid painkillers constipate and why the receptors are of interest as a target for gut diseases at all. In cell experiments and in gut organoids, that is, mini gut pieces grown in the lab, naltrexone promoted wound healing of the lining and reduced cell stress.

The body also has its own pain-dampening system in which endorphins play a role. Exercise, sleep and relaxation also increase these body-own signals, and stress dampens them. This explains why the boundaries between drug effect, expectation and lifestyle are so blurred in pain and fatigue.

The liver plays the main role in breakdown. Naltrexone is converted there and excreted via the kidney, which is why liver and kidney values are part of the medical assessment.

Disrupted state: causes and effects

What users report often sounds very positive: less pain, more energy, better sleep. In four small before-and-after studies on long Covid with 155 people in total, fatigue, pain and concentration problems decreased markedly. A study with a placebo Placebo A dummy treatment without an active ingredient. Comparing with it shows how much a remedy achieves beyond expectation and chance. group was not available in 2026, and without one a real effect cannot be separated from expectation and natural course. Especially in long Covid, many symptoms improve by themselves over time.

Why comparison groups matter so much: with complaints such as pain, tiredness and irritable bowel, a large share of people improve even with an inactive tablet; in IBS Irritable bowel syndrome Recurring abdominal pain linked to bowel movements, without tests finding another cause. Today it is understood as a disorder of gut–brain interaction. More in the chapter “The gut-brain axis” studies often clearly more than one in five to one in three. Symptoms also fluctuate, and people often start a new treatment just in a bad phase; afterwards things improve again for purely statistical reasons. That does not make personal reports worthless, but they do not prove an effect.

In Crohn’s disease this pattern repeats. In an open observation of 47 people with inflammatory bowel disease Inflammatory bowel disease Umbrella term for Crohn’s disease and ulcerative colitis: long-term, relapsing inflammation of the gut that needs medical treatment. More in the chapter “Immune system and inflammation”, 74.5 per cent improved, and a small placebo-controlled study with 34 adults also saw benefits. The 2018 Cochrane review nevertheless considered the evidence too thin. A larger Dutch study was stopped early in 2026 because no benefit was apparent: the lining healed in 1 of 18 people on LDN and in 3 of 16 on placebo, and clinical remission was even more common on placebo. Only fatigue was somewhat lower with LDN.

In fibromyalgia, early small studies had raised hope. Two larger, careful studies with about 100 women each found in 2024 and 2026 no meaningful difference from placebo for pain, not even after 12 months.

For irritable bowel there is only an open pilot study from 2006 with 42 people and an even lower dose: 76 per cent reported improvement, and pain-free days rose from 0.5 to 1.25 per week. Without a placebo group this cannot be separated from the placebo effect, which is large in IBS. We found no study on SIBO Small intestinal bacterial overgrowth (SIBO) Too many bacteria in the small intestine, where normally few live. Bloating and diarrhoea are typical; it is usually diagnosed with a breath test. More in the chapter “When the small intestine is too densely colonised” or on the small intestine’s cleansing wave Migrating motor complex A wave of muscle contractions that sweeps the stomach and small intestine empty about every one and a half to two hours when fasting. Eating interrupts it. More in the chapter “Intermittent fasting and meal timing: 16:8, 5:2 and Ramadan”.

An overview of 105 studies concluded in 2026 that positive results from uncontrolled studies were rarely confirmed in placebo studies. LDN is usually well tolerated. Vivid dreams and sleep problems are common, headaches or nausea less so. Important: naltrexone can cancel the effect of opioid painkillers and trigger withdrawal symptoms with regular opioid use. At the usual, high dose, raised liver values have been described; caution is needed with liver or kidney damage and in pregnancy and breastfeeding, and for the low dose there is hardly any data.

LDN is prescription-only and generally not approved for these uses. It is prescribed off-label Off-label An approved medicine is prescribed for a disease or at a dose for which it is not approved. This is permitted in many countries, but more responsibility lies with the doctor. and in some countries made up in pharmacies at the low dose. Offers from the internet without a prescription are uncontrolled in content and dose.