Naltrexone works by blocking the opioid receptors in your brain that are responsible for the pleasurable “buzz” you get from drinking alcohol. When those receptors are blocked, alcohol feels less rewarding, which over time reduces cravings and makes it easier to drink less or stop entirely. It’s one of three FDA-approved medications for alcohol use disorder and is available as a daily pill or a monthly injection.
How Alcohol Hijacks Your Brain’s Reward System
To understand what naltrexone does, it helps to know what alcohol does first. When you drink, your brain releases its own natural opioids, called endorphins. These endorphins activate opioid receptors, which in turn trigger a surge of dopamine in a brain region called the nucleus accumbens, the core of your brain’s reward circuit. That dopamine surge is what makes drinking feel good: the warmth, the relaxation, the mild euphoria.
Over time, your brain learns to associate alcohol with that reward signal. Cravings build. Drinking becomes harder to control, not because of willpower failure, but because the reward circuitry has been chemically conditioned to want more.
Naltrexone Blocks the Reward Signal
Naltrexone is an opioid receptor antagonist, meaning it physically attaches to opioid receptors and prevents endorphins from activating them. It has the strongest affinity for a specific type called the mu-opioid receptor. At the standard 50 mg oral dose, brain imaging studies show it blocks roughly 95% of mu-opioid receptors. With those receptors occupied, the chain reaction that normally leads to a dopamine surge in the nucleus accumbens is interrupted.
The practical effect is straightforward: if you drink while taking naltrexone, alcohol still impairs you, but it doesn’t feel as rewarding. The buzz is muted. Many people describe it as drinking feeling “flat” or pointless. Over weeks and months, this weakened reward signal reduces the urge to drink because your brain is gradually unlearning the association between alcohol and pleasure.
Naltrexone does not make you sick if you drink (that’s a different medication, disulfiram). It also doesn’t cause intoxication or dependence on its own. It simply dulls the payoff.
Two Ways to Take It
The oral form is a 50 mg tablet taken once daily. It’s the most widely prescribed version and is relatively inexpensive, especially as a generic. The main challenge is remembering to take it every day, which can be difficult for anyone, particularly during periods of high stress or relapse.
The extended-release injectable form is administered once a month by a healthcare provider. It removes the daily decision entirely, which can be a significant advantage if adherence is a concern. The injection delivers a steady dose over four weeks, so you don’t have gaps in coverage if you miss a pill.
The Sinclair Method: Taking It Only When You Drink
Some clinicians prescribe naltrexone using a targeted approach called the Sinclair Method. Instead of taking it daily, you take a 50 mg tablet about one hour before you plan to drink. The idea is to ensure the opioid receptors are blocked every time alcohol is consumed, which allows the brain’s reward conditioning to gradually extinguish. On days you don’t drink, you don’t take the medication.
An open-label trial in Finland using this protocol found that about 78% of patients were considered treatment successes. Among those, average drinking dropped to about 9 drinks per week, and 26% reached full abstinence, even though only 3% of participants had listed abstinence as their goal. The approach appeals to people who aren’t ready or willing to quit entirely but want to regain control over how much they drink.
How It Compares to Other Medications
Three medications are FDA-approved for alcohol use disorder: naltrexone, acamprosate, and disulfiram. They work differently and suit different situations.
Disulfiram takes a punishment-based approach. It blocks your body’s ability to break down alcohol, so drinking while taking it causes nausea, flushing, and a rapid heartbeat. In a randomized trial comparing all three drugs over 52 weeks, disulfiram outperformed both naltrexone and acamprosate in measures like time to first drink, number of abstinent days, and weekly alcohol consumption. But its effectiveness depends entirely on taking it consistently, and many people stop because of the unpleasant reactions or simply because they want to be able to drink.
Acamprosate works on a different brain system (the glutamate pathway) and is thought to ease the general discomfort and anxiety that come with early sobriety. In the same trial, naltrexone and acamprosate performed similarly on most drinking outcomes, though naltrexone showed greater improvement in alcohol dependence severity scores at the six-month mark.
No single medication is best for everyone. Naltrexone’s advantage is that it can be used whether your goal is abstinence or reduced drinking, and it doesn’t require you to avoid alcohol entirely to be effective.
Common Side Effects
The most frequently reported side effect is nausea, which tends to be worst in the first week or two and often fades as your body adjusts. Other common side effects include headache, dizziness, sleepiness, decreased appetite, trouble sleeping, muscle cramps, and joint pain. Some people experience vomiting or cold-like symptoms. Most side effects are mild enough that they don’t lead people to stop treatment, but if nausea is persistent, taking the pill with food or starting at a lower dose can help.
Important Safety Considerations
Because naltrexone blocks opioid receptors, you must be free of all opioids for at least 5 to 7 days before starting it. If you take naltrexone while opioids are still in your system, it will trigger precipitated withdrawal, a sudden and intense onset of withdrawal symptoms that can be extremely uncomfortable. This includes prescription painkillers, heroin, and opioid-based cough medications.
While you’re on naltrexone, opioid pain medications won’t work effectively. If you need emergency surgery or pain management, it’s important that your medical team knows you’re taking it so they can use non-opioid alternatives.
Liver health is another consideration. Naltrexone is processed by the liver, and there have been concerns about liver enzyme elevations at high doses. Current guidelines from the American Association for the Study of Liver Diseases consider it acceptable for patients with compensated liver disease when monitored closely, but it should be avoided in people with severe liver impairment. Your provider will typically check liver function before starting treatment and periodically afterward.
What to Realistically Expect
Naltrexone is not a cure. It’s a tool that makes behavior change easier by quieting the neurological drive to drink. Most people notice a reduction in cravings within the first week or two, though the full effect on drinking patterns often develops over several months as the brain’s reward associations weaken.
It works best when combined with some form of behavioral support, whether that’s formal therapy, a recovery program, or even regular check-ins with a prescribing provider. The medication handles the neurochemistry; the behavioral component helps you build new patterns and address the situations that trigger drinking. Together, they’re considerably more effective than either approach alone.