Generic Name: Naltrexone
Dosage Forms: Intramuscular injection (380 mg), Oral tablet (50 mg)
Drug Classes: Antidotes, Drugs used in alcohol dependence

What is Naltrexone?

Naltrexone is a prescription medication used to treat alcohol use disorder (AUD) and opioid use disorder (OUD). It helps reduce cravings and manage physiological dependence. Naltrexone works by blocking the effects of alcohol and opioid medications, preventing the euphoria and intoxication they cause. It also reduces the urge to use these substances.

For alcohol use disorder, Naltrexone helps reduce drinking behavior and prevents relapses. Over time, cravings for alcohol decrease.

For opioid use disorder, Naltrexone blocks euphoria and reduces physical dependence on opioids, such as heroin, morphine, and codeine, helping prevent relapses and maintain sobriety.

Low dose Naltrexone (LDN) is used off-label (not FDA-approved) for conditions like fibromyalgia, Crohn’s disease, multiple sclerosis, and complex regional pain syndrome, potentially acting as an anti-inflammatory agent in the central nervous system.

Naltrexone is available as an intramuscular injection (Vivitrol) and oral tablets. The branded tablets (Revia, Depade) have been discontinued, but generic versions are available.

Mechanism of Action (MOA)

Naltrexone is an opioid antagonist that works by blocking the mu opioid receptor. It also influences the hypothalamus, pituitary gland, and adrenal gland (HPA axis) to reduce alcohol consumption.

Approved Uses

Naltrexone is FDA-approved for:

Alcohol Dependence: To reduce alcohol consumption and prevent relapse.
Opioid Use Disorder: To block the effects of exogenously administered opioids and prevent relapse after detoxification.
Patients should stop drinking alcohol or using opioids before starting Naltrexone. An opioid-free interval of 7 to 10 days is recommended for those dependent on short-acting opioids, and patients transitioning from buprenorphine or methadone may require up to two weeks.

Side Effects

Common Side Effects:

Nausea, vomiting, loss of appetite
Joint pain, muscle cramps
Headache, dizziness, drowsiness
Sleep problems (insomnia)
Tooth pain, cold symptoms (stuffy nose, sneezing, sore throat)
Anxiety, nervousness
Serious Side Effects:

Allergic Reactions: Hives, difficulty breathing, swelling of the face, lips, tongue, or throat.
Opioid Withdrawal Symptoms: Craving, sweating, yawning, fever, stomach pain, vomiting, diarrhea, watery eyes, runny or stuffy nose, tingling, goosebumps, body aches, shaking, muscle twitching, trouble sleeping, anxiety, depression, fearfulness.
Respiratory Issues: Weak or shallow breathing, persistent cough, trouble breathing.
Gastrointestinal Problems: Severe nausea, vomiting, diarrhea, pain, or swelling at the injection site.
Liver Problems: Symptoms include upper right side stomach pain, dark urine, tiredness, vomiting, loss of appetite, clay-colored stools, jaundice.
Mental Health Issues: Unusual mood or behavior changes, loss of interest in activities, new sleep problems, thoughts of self-harm.

Precautions 

Before Taking Naltrexone
Do not use Naltrexone if you:

Are allergic to it.
Are currently addicted to opioids.
Are having withdrawal symptoms from opioid addiction.
Are using any opioid pain medicine.
Have failed the naloxone challenge test or have a positive urine screen for opioids.
Have recently used opioid medications, including methadone, buprenorphine, or tramadol.

Pregnancy and Breastfeeding

Pregnancy: The effects of Naltrexone on an unborn baby are unknown. Use only if the benefits outweigh the risks.
Breastfeeding: It is unknown whether Naltrexone passes into breast milk when administered by injection. Naltrexone from tablets does pass into breast milk. Consult your healthcare provider about whether to breastfeed or take Naltrexone, as you should not do both.
Important Information
Risk of Opioid Overdose: Naltrexone blocks opioid effects, so taking large amounts of opioids can lead to overdose or death, especially after detoxification, when sensitivity to opioids may increase.
Injection Site Reactions: Severe reactions, including tissue necrosis, may occur at the injection site. Immediate medical attention is required for intense pain, large swelling, lumps, blisters, open wounds, or dark scabs.
Sudden Opioid Withdrawal: Using opioids 7 to 14 days before starting Naltrexone may cause sudden withdrawal symptoms, which can be severe and may require hospitalization.
Liver Damage or Hepatitis: Naltrexone can cause liver damage. Watch for symptoms like prolonged stomach pain, dark urine, yellowing of the eyes, and tiredness.

Dosing Information

Naltrexone Tablets:

Alcohol Dependence: 50 mg once daily.
Opioid Use Disorder: Start with 25 mg, then increase to 50 mg daily if no withdrawal symptoms occur.
Naltrexone Injection:

Alcohol and Opioid Use Disorders: 380 mg intramuscularly every 4 weeks or once a month, alternating injection sites.
Missed Dose and Overdose
Missed Dose (Tablets): Take as soon as possible, but skip if it’s almost time for your next dose.
Missed Dose (Injection): Reschedule as soon as possible.
Overdose: Contact a healthcare provider or emergency services immediately.
Storage
Tablets: Store at 20° to 25°C.
Injection: Store refrigerated at 2° to 8°C. Do not expose to temperatures above 25°C for more than 7 days. Do not freeze.

Ingredients

Active Ingredient: Naltrexone (injection), Naltrexone hydrochloride (tablets).
Inactive Ingredients (Tablets): Vary by formulation; check the product label.

Note: 

The brand name displayed above is specific to this product. Brand names can vary depending on the manufacturer.