NaltrexoneEdit

Naltrexone is an opioid receptor antagonist used in the treatment of opioid dependence and some forms of alcohol use disorder. By blocking mu-opioid receptors, it dampens the rewarding effects of opioids and can reduce the urge to drink for some individuals. It has become a fixture in modern addiction medicine, with both oral and long-acting injectable forms available. In the United States, it is marketed under brand names such as ReVia for the oral formulation and Vivitrol for the extended-release injectable form. For more on the pharmacology underlying its action, see the mu-opioid receptor and opioid receptor antagonist entries.

The drug’s development and deployment sit at the intersection of medical science and public policy. Proponents emphasize its non-addictive mechanism and its usefulness for patients who prefer a non-agonist approach to treatment. Critics, however, point to adherence challenges, the need for a period of opioid abstinence before initiation, and questions about long-term outcomes in certain populations. Across a spectrum of clinical settings, naltrexone is positioned as one option within a broader toolbox of treatments for substance-use disorders. See Naltrexone for the core entry and Alcohol use disorder and Opioid use disorder for related conditions.

Medical overview

Mechanism of action

Naltrexone binds with high affinity to mu-opioid receptors, acting as a competitive antagonist. By occupying these receptors, it blocks the effects of endogenous opioids and any opioids that might be taken while the drug is active. Its action helps blunt the reinforcing properties of opioids and can reduce the motivation to use opioids again. It has some activity at other opioid receptor subtypes, but its clinical effects are driven primarily by mu-receptor antagonism. See mu-opioid receptor and opioid receptor antagonist for more detail.

Pharmacokinetics and forms

Oral naltrexone is absorbed and metabolized in the liver, with a significant portion of the dose rendered inactive by first-pass metabolism, and an active metabolite known as 6-beta-naltrexol contributing to its overall effect. The oral form has a shorter duration of receptor blockade, which is why daily dosing is required in most regimens. The extended-release injectable form, marketed as Vivitrol, provides approximately a one-month duration of action after a single intramuscular injection. This long-acting formulation is designed to improve adherence in patients who struggle with daily dosing. See 6-beta-naltrexol and long-acting injectable for related pharmacology concepts.

Indications and clinical use

Opioid use disorder: Naltrexone is prescribed for adults who have already completed an appropriate detoxification or made themselves opioid-free, to help prevent relapse. It is not an opioid substitute and does not produce withdrawal relief in the way that agonist therapies do. See Opioid use disorder.
Alcohol use disorder: Some patients with problematic drinking patterns experience fewer heavy-drinking days and improved control when taking naltrexone. The magnitude of benefit varies by individual and comorbidity. See Alcohol use disorder.

Dosing and administration

Oral: Commonly 50 mg once daily, with tapering or adjustments as clinically indicated.
Extended-release: 380 mg intramuscular injection every 28 days. Dosing considerations include hepatic function and ensuring that the patient is opioid-free prior to initiation to avoid precipitated withdrawal. See ReVia and Vivitrol for brand-specific formulations.

Contraindications and safety

Naltrexone is contraindicated in individuals who are currently opioid-dependent and have not completed detoxification, due to the risk of precipitating withdrawal. It should be used with caution in patients with liver impairment or active liver disease, given potential hepatotoxicity at high doses or with prolonged use. Possible adverse effects include nausea, headache, fatigue, dizziness, and sleep disturbances, with injection-site reactions more common with the extended-release form. See Naltrexone adverse effects for a fuller catalog of safety data.

Interactions and cautions

Because naltrexone blocks opioid receptors, taking opioid agonists for pain relief while on naltrexone will be ineffective and can provoke withdrawal. This has important implications in pain management and other medical care contexts. Clinicians must screen for opioid exposure and coordinate care to avoid unsafe or painful gaps in analgesia. See Drug interaction and Opioid withdrawal for related topics.

Efficacy and clinical debates

Opioid use disorder

Clinical trials show that naltrexone can reduce relapse risk for some adults with opioid use disorder, particularly when adherence is achieved and maintained. The extended-release formulation has been shown to improve medication adherence compared with daily oral dosing, which is a significant factor in real-world effectiveness. Critics note that for some patients, especially those who fail to adhere to any pharmacotherapy, alternative approaches such as methadone or buprenorphine (which activate opioid receptors to some degree) may yield more reliable long-term outcomes. See Buprenorphine and Methadone for comparison.

Alcohol use disorder

In alcohol use disorder, naltrexone has demonstrated modest but clinically meaningful reductions in heavy drinking days for some patients. Effect sizes vary, and not everyone responds. Proponents argue that naltrexone offers a non-addictive pharmacological option that complements psychosocial therapies, aligning with broader goals of improving health outcomes without mandating abstinence in all cases. Critics contend that the public-health impact depends heavily on patient selection, support services, and adherence. See Alcohol use disorder and Behavioral therapy.

Public policy and practice

The deployment of naltrexone intersects with budget priorities, healthcare access, and criminal-justice policy. Supporters emphasize that effective pharmacotherapies can reduce relapse, lower healthcare costs over time, and decrease crime and humanitarian harm among people with substance-use disorders. Critics worry about affordability, the risk of coercive treatment in some settings, and whether programs emphasize medication at the expense of comprehensive care. The long-acting injectable form is especially relevant to discussions about adherence and resource allocation in high-need communities. See Addiction treatment and Criminal justice and health policy.

Controversies and debates (from a practical, policy-oriented perspective)

Adherence versus accessibility: The oral form requires daily dosing, which can be a hurdle for many patients. The extended-release injectable mitigates this but raises upfront costs and access questions. The trade-off between adherence and affordability is central to program design. See Vivitrol.
Role alongside other therapies: Some argue for aggressive use of opioid agonist therapies in appropriate patients, while others emphasize non-opioid approaches like naltrexone to support autonomy and reduce diversion risk. The best practice often depends on patient preferences, safety considerations, and local resources. See Buprenorphine and Methadone.
Criminal-justice applications: Programs in which naltrexone is used to reduce relapse risk among offenders spark debates about consent, coercion, and public safety. Proponents say that reducing relapse and crime is a legitimate objective; critics worry about civil-liberties concerns and the possibility of substituting punishment for genuine treatment. See Criminal justice and health policy.
Cost and coverage: High-cost formulations can strain budgets in public systems and some private plans. Advocates emphasize reducing long-term costs from relapse and hospitalizations, while opponents push for broader access to affordable generics and community-based supports. See Health economics.

History and development

Naltrexone emerged from mid-20th-century efforts to create non-addictive treatments for opioid dependency. Brand names like ReVia and later Vivitrol reflect successive iterations aimed at improving tolerability and adherence. The drug's role expanded as evidence accumulated for both opioid dependence and certain patterns of alcohol use, leading to its current status as a widely prescribed option in both consequence management and relapse-prevention strategies. See Pharmacology and Drug development for context.