Naltrexone Side Effects

Medically reviewed by Philip Thornton, DipPharm. Last updated on Jul 5, 2024.

Applies to naltrexone: oral capsule, oral tablet.

Other dosage forms:

• intramuscular powder for suspension extended release

Precautions

It is very important that your doctor check your progress at regular visits. Your doctor may want to do certain blood tests to see if the medicine is causing unwanted effects.

This medicine blocks the "high" feeling you get from narcotic (opioid) drugs, including heroin. Since naltrexone may make you more sensitive to lower doses of opioids than you have previously used, you should not use heroin or any other narcotic drugs to overcome what the medicine is doing. You could overdose and develop serious problems.

This medicine may cause serious problems with your liver. Call your doctor right away if you start having dark urine, pain in the upper stomach, or yellowing of the eyes or skin while you are using this medicine.

This medicine may increase thoughts of suicide. Tell your doctor right away if you start to feel more depressed. Also tell your doctor right away if you have thoughts about hurting yourself. Report any unusual thoughts or behaviors that trouble you, especially if they are new or get worse quickly. Make sure your caregiver knows if you feel tired all the time, sleep a lot more or a lot less than usual, feel hopeless or helpless, or if you have trouble sleeping, get upset easily, have a big increase in energy, or start to act reckless. Also tell your doctor if you have sudden or strong feelings, such as feeling nervous, angry, restless, violent, or scared.

Remember that use of naltrexone is only part of your treatment. Be sure that you follow all of your doctor's orders, including seeing your therapist and/or attending support group meetings on a regular basis.

Do not try to overcome the effects of naltrexone by taking narcotics. To do so may cause coma or death. You may be more sensitive to the effects of narcotics than you were before beginning naltrexone therapy.

Naltrexone also blocks the useful effects of narcotics. Always use a non-narcotic medicine to treat pain, diarrhea, or a cough. If you have any questions about the proper medicine to use, check with your doctor.

Naltrexone will not prevent you from becoming impaired when you drink alcohol. Do not take naltrexone in order to drive or perform other activities while under the influence of alcohol.

This medicine may cause some people to become dizzy, drowsy, or less alert than they are normally. If any of these side effects occur, do not drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert while you are taking naltrexone.

Never share this medicine with anyone else, especially someone who is using narcotics. Naltrexone causes withdrawal symptoms in people who are using narcotics.

Tell all medical doctors, dentists, and pharmacists you go to that you are taking naltrexone.

It is recommended that you carry identification stating that you are taking naltrexone. Identification cards may be available from your doctor.

Common side effects of naltrexone

Some side effects of naltrexone may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Serious side effects of naltrexone

Along with its needed effects, naltrexone may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking naltrexone:

For healthcare professionals

Applies to naltrexone: compounding powder, intramuscular powder for injection extended release, oral capsule, oral tablet.

Nervous system adverse events

• Very common (10% or more): Headache (25%), dizziness/syncope (13%)
• Common (1% to 10%): Somnolence/sedation
• Frequency not reported: Lethargy, cerebral arterial aneurysm, convulsions, disturbance in attention, dysgeusia, mental impairment, migraine, ischemic stroke, paresthesia^[Ref]

Psychiatric

• Very common (10% or more): Insomnia/sleep disorder (14%), anxiety (12%)
• Common (1% to 10%): Depression
• Uncommon (0.1% to 1%): Suicide attempt/ideation
• Frequency not reported: Irritability, abnormal dreams, agitation, alcohol withdrawal syndrome, euphoric mood, delirium, libido decreased^[Ref]

Gastrointestinal

• Very common (10% or more): Nausea (33%), vomiting NOS (14%), diarrhea (13%), abdominal pain (11%)
• Common (1% to 10%): Dry mouth, toothache
• Frequency not reported: Abdominal discomfort, colitis, constipation, flatulence, gastroesophageal reflux disease, gastrointestinal hemorrhage, hemorrhoids, pancreatitis acute, paralytic ileus^[Ref]

Hepatic

• Very common (10% or more): Alanine aminotransferase increased (13%), aspartate aminotransferase increased (10%)
• Common (1% to 10%): Gamma-glutamyltransferase increased
• Frequency not reported: Lymphadenopathy including cervical adenitis, white blood cell count increased, cholecystitis acute, cholelithiasis^[Ref]

Local

• Very common (10% or more): Injection site tenderness (45%), injection site induration (35%), injection site pain (17%), other injection site reaction (primarily nodules, swelling) (15%), injection site pruritus (10%)
• Common (1% to 10%): Injection site ecchymosis^[Ref]

Musculoskeletal

• Very common (10% or more): Arthralgia/arthritis/joint stiffness (12%)
• Common (1% to 10%): Back pain/stiffness, muscle cramps
• Frequency not reported: Chills, joint stiffness, muscle spasms, myalgia, pain in limb^[Ref]

Other

• Very common (10% or more): Asthenic conditions (23%)
• Frequency not reported: Chest pain, chest tightness, abortion missed^[Ref]

Cardiovascular

• Frequency not reported: Angina pectoris, angina unstable, atrial fibrillation, cardiac failure congestive, coronary artery atherosclerosis, myocardial infarction, palpitations, deep vein thrombosis^[Ref]

Respiratory

• Frequency not reported: Chronic obstructive pulmonary disease, dyspnea, pharyngolaryngeal pain, sinus congestion^[Ref]

Dermatologic

• Common (1% to 10%): Rash
• Frequency not reported: Face edema, night sweats, pruritus, sweating increased^[Ref]

Metabolic

• Very common (10% or more): Anorexia/appetite decreased NOS/appetite disorder NOS (14%)
• Frequency not reported: Weight decreased, weight increased, appetite increased, dehydration^[Ref]

Renal

• Very common (10% or more): Abnormal creatinine phosphokinase levels (17%)^[Ref]

Hematologic

• Frequency not reported: Eosinophil counts increased, decreased platelet count^[Ref]

Ocular

• Frequency not reported: Conjunctivitis, vision blurred^[Ref]

Hypersensitivity

• Frequency not reported: Hypersensitivity reaction (including angioneurotic edema and urticaria)
• Postmarketing reports: Anaphylaxis^[Ref]

Immunologic

• Very common (10% or more): Pharyngitis (11%)
• Common (1% to 10%): Nasopharyngitis
• Frequency not reported: Seasonal allergies^[Ref]

See also:

Frequently asked questions

• What is low dose naltrexone (LDN)?
• What happens if you drink alcohol while taking naltrexone?
• What to avoid when taking naltrexone?
• Should I take naltrexone in the morning or at night?
• Does naltrexone cause weight gain?
• Acamprosate vs naltrexone: How do they compare?
• How long does naltrexone take to work?
• How does naltrexone make you feel?
• What is the mechanism of action for naltrexone?

Further information

Naltrexone side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer