Low-dose naltrexone (LDN) is an off-label use of naltrexone at doses lower than those approved for alcohol- or opioid-use disorders. It is sometimes prescribed for chronic pain, fibromyalgia, or inflammatory conditions, but evidence varies by condition and it is not an FDA-approved treatment for most of these uses.
Because LDN is off-label, dosing and monitoring should come from a qualified prescriber. Do not increase, decrease, start, or stop it based on internet advice alone.
Common Side Effects
Reported effects can include vivid dreams or sleep disturbance, headache, nausea, stomach discomfort, fatigue, and occasionally mood changes. The true frequency of side effects at low doses is not as well established as it is for standard-dose naltrexone.
The Most Important Safety Issue: Opioids
Naltrexone blocks opioid receptors. Taking it while opioids are still in the body can trigger sudden withdrawal in someone who is opioid-dependent and can also block the pain-relieving effects of opioid medicines.
Tell your prescriber about all opioid use, including prescription pain medicines, cough products that contain opioids, and any recent non-prescribed opioid use. Do not try to determine an opioid-free interval on your own.
Liver Safety
Naltrexone can affect the liver, especially at higher exposures or in people with existing liver disease. Seek medical advice for severe abdominal pain, persistent nausea or vomiting, dark urine, or yellowing of the skin or eyes.
Pregnancy and Breastfeeding
If you are pregnant, planning pregnancy, or breastfeeding, discuss the risks and benefits with your clinician. Do not assume that “low dose” automatically means risk-free.
Does LDN Cause Weight Loss?
LDN by itself is not an approved weight-loss treatment. Naltrexone is part of an approved combination medicine with bupropion for weight management, but that is different from using low-dose naltrexone alone. Claims that LDN reliably causes weight loss are not well established.
When to Get Medical Help
Seek urgent help for trouble breathing, facial or throat swelling, severe confusion, or signs of a serious allergic reaction. Contact your prescriber promptly for persistent side effects, major mood changes, or concerns about opioid exposure.
Bottom Line
LDN may be useful in selected patients, but many uses remain off-label and evidence is limited or mixed. The safest approach is individualized prescribing, careful review of opioid use, and monitoring for side effects rather than self-adjusting the dose.
Reliable Sources
Last reviewed for medical accuracy: September 2026.