Naltrexone is a prescription medication used to treat alcohol use disorder (AUD) and opioid use disorder (OUD). It is not a cure for addiction but a tool to support recovery, intended for use alongside counseling and support groups. Naltrexone helps individuals manage their dependencies by targeting specific pathways in the brain associated with substance use.
Naltrexone’s Mechanism of Action
Naltrexone is an opioid antagonist, meaning it blocks the effects of opioid substances. It binds to opioid receptors in the brain, particularly the mu-opioid receptors, without activating them. This action is like a key that fits into a lock but doesn’t turn it; by occupying the lock, it prevents other keys—such as heroin, prescription painkillers, or the body’s own endorphins—from being inserted and producing their usual effects.
By occupying these receptors, naltrexone prevents the euphoric and sedative feelings produced by opioids. This blockade also applies to the endorphins released during alcohol consumption, which is central to its effect on AUD. As a pure antagonist, it has little to no activating properties of its own; its primary role is to block these receptor sites and alter the chemical responses associated with substance use.
The medication is absorbed orally and metabolized in the liver into an active metabolite, 6-beta-naltrexol, which also contributes to its effects. The duration of this blockade is dose-dependent, with higher doses providing a longer-lasting effect.
Impact on Alcohol and Opioid Use
For individuals with alcohol use disorder, consuming alcohol triggers the release of endorphins, the body’s natural opioids. These endorphins bind to opioid receptors and produce feelings of pleasure, which reinforces the desire to drink. Naltrexone interferes with this cycle by blocking those receptors and diminishing the rewarding feedback from drinking.
This interruption helps extinguish the learned association between alcohol and reward over time. While naltrexone does not prevent the intoxicating effects of alcohol or treat alcohol withdrawal, it can reduce cravings and help people drink less or stop altogether. Patients taking naltrexone are less likely to experience a full relapse if they drink, as the substance no longer provides the same positive reinforcement.
In the context of opioid use disorder, naltrexone’s blockade makes the act of taking drugs like heroin or oxycodone feel pointless, as the anticipated high is absent. This serves as a powerful deterrent, helping to prevent relapse in individuals who have completed detoxification. Because naltrexone has no potential for abuse or dependence, it offers a distinct approach to treatment.
Physical and Psychological Side Effects
Naltrexone treatment can cause side effects, which are often mild and may lessen as the body adjusts. Common side effects can include:
- Nausea
- Headaches
- Dizziness
- Fatigue
- Anxiety or nervousness
- Difficulty sleeping
- Abdominal pain
These symptoms are generally temporary, but persistent issues should be discussed with a healthcare provider.
More serious side effects require immediate medical attention. A primary concern is the potential for liver damage or hepatitis, especially at high doses. Symptoms like persistent stomach pain, dark urine, or yellowing of the eyes must be reported to a doctor. For the injectable form, severe reactions at the injection site can occur, including pain, swelling, or blistering.
Some individuals may experience psychological effects, including mood changes like depression or, in rare cases, suicidal thoughts. An allergic reaction is also possible and may present as a skin rash or swelling. Any of these more serious symptoms require urgent medical care.
Precautions and Medical Supervision
Medical supervision is necessary when using naltrexone. A person must be completely free of all opioids for 7 to 10 days before starting the medication. This occurs because naltrexone rapidly displaces opioids from their receptors, causing an abrupt and severe onset of withdrawal symptoms like nausea, vomiting, and muscle aches.
Before beginning treatment, healthcare providers conduct liver function tests to ensure the patient’s liver is healthy enough to metabolize the drug. Ongoing monitoring of liver health may be necessary throughout treatment to manage the risk of injury.
Naltrexone is available as a daily oral tablet (ReVia) or a monthly intramuscular injection (Vivitrol). The choice depends on a patient’s circumstances and ability to adhere to a daily schedule. The long-acting injection provides a consistent level of medication and is an option for those who struggle with daily dosing.