Naltrexone Hydrochloride
Pronunciation: (nal-TREX-own).
- Generic name
- naltrexone hydrochloride
- Brand names
- Vivitrol
- Drug class
- Opioid receptor antagonist
Availability and supply rules vary by country
Trade names by country: Canada
Australia: · Full directory
What naltrexone hydrochloride is and how it works
Uses, formulations, monitoring, and supply rules can differ by patient, product, and country. Follow the exact local product information and professional advice.
Mechanism of action: how naltrexone hydrochloride works
Naltrexone is a competitive opioid receptor antagonist with highest affinity for the mu-opioid receptor. It blocks the effects of endogenous and exogenous opioids, preventing opioid-induced euphoria and reinforcing effects. In alcohol dependence, naltrexone is thought to modulate the dopaminergic mesolimbic pathway, reducing the rewarding effects of alcohol. (2) (1)
What naltrexone hydrochloride is used for
Alcohol use disorder (alcohol dependence)
FDA-approved to support abstinence as part of a comprehensive treatment plan that includes counseling and support. (1)
Opioid use disorder — blockade of exogenous opioid effects and relapse prevention after opioid detoxification
FDA-approved to block the effects of opioids and help prevent relapse after a patient has been medically withdrawn from opioids; must not be started until the patient has been opioid-free for at least 7-10 days. (1)
Before taking naltrexone hydrochloride
Do not take / not appropriate for
- Contraindicated in patients with current physiological opioid dependence, acute opioid withdrawal, acute hepatitis, or severe hepatic impairment. (Contraindication) (1)
Tell your clinician about
(1)How to take naltrexone hydrochloride
- General Instructions: Take naltrexone exactly as prescribed by your healthcare provider. Do not take more or less than directed.. Adult Dosing: For alcohol dependence: 50 mg orally once daily. For opioid dependence: 50 mg orally once daily, or 380 mg intramuscularly every 4 weeks (extended-release injection).. Pediatric Dosing: Safety and efficacy in children under 18 years have not been established; use is not generally recommended.. Administration: Tablets should be taken with or without food. The injection is administered by a healthcare professional into the gluteal muscle.. When To Stop: Do not stop taking naltrexone without consulting your doctor. Stopping suddenly may increase the risk of relapse.. Storage: Store tablets at room temperature away from moisture and heat. Keep out of reach of children.
- This page does not provide a dose calculator. Dosing must follow the prescriber, pharmacist, or product label.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1)
Missed dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and resume your regular schedule. Do not double the dose to catch up.
Overdose
In case of overdose, seek emergency medical attention immediately. Symptoms may include severe nausea, vomiting, abdominal pain, or confusion. There is no specific antidote; treatment is supportive. (1)
Side effects
Side effects and their urgency vary; report severe, persistent, or concerning symptoms to a healthcare professional.
Nausea and vomiting
Incidence: Common
Loss of appetite
Incidence: Common
Joint pain and muscle cramps
Incidence: Common
Headache and dizziness
Incidence: Common
Drowsiness and sleep problems (insomnia)
Incidence: Common
Serious warnings
Risk of liver injury — serious
Symptoms: Risk of liver injury: naltrexone can cause liver enzyme elevations at higher-than-recommended doses; monitor for signs of hepatitis or liver problems (yellowing skin/eyes, dark urine, unusual tiredness, abdominal pain). Note: the FDA removed the boxed (black-box) warning for naltrexone hepatotoxicity in 2013 after review found no evidence of liver damage at the recommended dose, but hepatotoxicity remains an ordinary warning/precaution on the current label — this content model was specifically checked for a missed boxed warning and confirmed none currently applies. Do not use if currently dependent on opioids or in withdrawal. Opioid sensitivity may increase after stopping naltrexone, raising overdose risk if opioids are used again. Use caution in patients with depression or suicidal thoughts.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (1)
Contraindications — serious
Symptoms: Contraindications: current physiological opioid dependence, acute opioid withdrawal, a positive opioid urine screen or failed naloxone challenge test, patients receiving opioid analgesics, or hypersensitivity to naltrexone. Note: acute hepatitis and severe hepatic impairment were REMOVED as formal contraindications in a 2013 FDA label update (previously listed); they remain important cautions requiring clinician judgment and liver monitoring, not absolute contraindications on the current label. Use with caution in hepatic or renal impairment, and in patients with depression or suicidal ideation.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Recorded interactions | Naltrexone may interact with opioid-containing medications, including cough, cold, or pain medicines. Using opioids while on naltrexone can cause sudden withdrawal symptoms. Inform your doctor about all prescription, over-the-counter, and herbal products you use. | (2) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
It is not known whether naltrexone will harm an unborn baby. This medicine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. If you are pregnant, planning to become pregnant, or become pregnant during treatment, seek medical advice promptly. (1)
Breastfeeding
Naltrexone from tablets passes into breast milk, and the general guidance is not to do both — breastfeed or take the tablets, not both — so talk with your healthcare provider about your feeding options before starting. For the extended-release injection, it is not known whether naltrexone passes into milk; discuss this specifically with your healthcare provider as well. (1)
Children
Frequency: Not applicable. Weight Based: Not recommended for pediatric use. Max Daily Dose: Not applicable. Max Single Dose: Not applicable. Age Restrictions: Safety not established in children (1)
Renal_impairment
Requires a primary-source research pass before this section can be completed. (1)
Hepatic_impairment
Requires a primary-source research pass before this section can be completed. (1)
Monitoring
(1)Storage
Tablets: store at room temperature (20-25C/68-77F), away from moisture and heat, out of reach of children. Extended-release injection (Vivitrol): this formulation MUST be stored refrigerated (2-8C/36-46F) — it is not a room-temperature product; storage and preparation are handled by the administering healthcare professional.
Professional information
Clinician-facing context only. This section does not replace current product labeling.
General
Indication: Alcohol use disorder and opioid use disorder (oral tablets)
Dose summary: Initial dose: 25 mg orally once; Maintenance dose: 50 mg orally once daily. Extended-release injectable (Vivitrol): 380 mg intramuscularly every 4 weeks.
Renal context: FDA label: caution is recommended when administering naltrexone to patients with renal impairment. The label does not give a specific numeric dose-reduction table for renal impairment; adequate studies in patients with severe renal impairment have not been conducted, so dosing should be individualized with clinician oversight in this group. (2) (1)
Hepatic guidance
FDA label: naltrexone exposure (AUC) is increased approximately 5-fold in patients with compensated liver cirrhosis and approximately 10-fold in patients with decompensated liver cirrhosis compared with people with normal liver function. Naltrexone does have extrahepatic (non-liver) metabolic pathways, unlike drugs cleared solely by the liver, but adequate studies in patients with severe hepatic impairment have not been conducted, and the label does not give a specific numeric dose-reduction table; naltrexone also carries a labeled risk of dose-dependent hepatocellular injury at higher-than-recommended doses, so liver function should be assessed and monitored by the prescriber before and during use in anyone with hepatic impairment.
Frequently asked questions
How long does naltrexone take to start working?
Naltrexone begins to block opioid receptors within 1–2 hours after oral administration. For alcohol dependence, it may take several days to notice reduced cravings.
Can I take naltrexone if I am still using opioids?
No. Starting naltrexone while opioids are in your system can cause sudden and severe withdrawal symptoms. You must be opioid-free for at least 7–10 days before starting.
Is naltrexone addictive?
No, naltrexone is not addictive and does not cause physical dependence.
Can naltrexone be used during pregnancy?
Naltrexone should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus. Discuss with your healthcare provider.
What happens if I use opioids after stopping naltrexone?
Your sensitivity to opioids may be increased after stopping naltrexone, raising the risk of overdose even with small doses.
How long do I need to take naltrexone?
The duration of treatment varies. Many people take naltrexone for several months to a year, depending on individual needs and response.
Does naltrexone help with cravings for alcohol?
Yes, naltrexone can help reduce cravings and the rewarding effects of alcohol, supporting abstinence.
What happens if I take too much Naltrexone?
Taking too much Naltrexone can lead to severe adverse effects, though it is not typically associated with respiratory depression like opioids. Symptoms of overdose may include severe nausea, vomiting, dizziness, and abdominal pain. If you suspect an overdose, it is crucial to seek immediate emergency medical attention. Do not attempt to self-treat or wait for symptoms to worsen.
Can I drink alcohol while taking Naltrexone?
Naltrexone is specifically prescribed to help reduce alcohol cravings and consumption in individuals with alcohol dependence. While it does not prevent the intoxicating effects of alcohol, it can diminish the pleasurable feelings associated with drinking, potentially leading to reduced intake. However, it is generally recommended to avoid alcohol consumption while on Naltrexone to maximize treatment effectiveness and prevent potential adverse interactions or liver strain.
Is Naltrexone safe during pregnancy?
Naltrexone's safety during pregnancy is not definitively established, and it is categorized as Pregnancy Category C. This means that animal reproduction studies have shown an adverse effect on the fetus, but there are no adequate and well-controlled studies in humans. Therefore, Naltrexone should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus. Always consult your healthcare provider to discuss the risks and benefits if you are pregnant or planning to become pregnant.
What is the mechanism of action of naltrexone hydrochloride?
Naltrexone is a competitive opioid receptor antagonist with highest affinity for the mu-opioid receptor. It blocks the effects of endogenous and exogenous opioids, preventing opioid-induced euphoria and reinforcing effects. In alcohol dependence, naltrexone is thought to modulate the dopaminergic mesolimbic pathway, reducing the rewarding effects of alcohol. (2) (1)
What is the generic name of Naltrexone Hydrochloride?
The generic name is naltrexone hydrochloride. It is sold under brand names including Vivitrol.
What class of drug is naltrexone hydrochloride?
Naltrexone Hydrochloride is classed as: Opioid receptor antagonist.
References
- Drugs.com — Naltrexone consumer monograph · · accessed 2026-08-07 · source 1
- Clinician-authored medicine record for Naltrexone (MedGuideGlobal medicines database) · · accessed 2026-08-07 · source 2
- NALTREXONE HYDROCHLORIDE TABLET, FILM COATED [APHENA PHARMA SOLUTIONS - TENNESSEE, LLC ] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 3
- Naltrexone — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 4
- Naltrexone Hydrochloride — FDA approval record (Drugs@FDA ANDA091205)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 5
- naltrexone — RxNorm normalized drug concept (RXCUI 105069)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 6
Brand names by country
Single-ingredient naltrexone hydrochloride names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
Canada
- REVIA