Most people can start naltrexone for alcohol use disorder after at least 3 days without drinking, though 7 days is preferable. The key requirement is that signs of acute alcohol withdrawal have subsided before the first dose. Beyond that initial timing, there are a few medical prerequisites and a specific dosing ramp-up that affect when and how you begin.
The Abstinence Window Before Starting
FDA labeling recommends waiting until symptoms of acute alcohol withdrawal have fully resolved. In practice, this means a minimum of 3 days without alcohol, with 7 days considered ideal. The reason is straightforward: naltrexone can worsen nausea and other withdrawal symptoms if the body is still adjusting to the absence of alcohol. Starting too early makes side effects harder to distinguish from withdrawal and increases the chance you’ll stop the medication before it has a chance to work.
For people with a long history of heavy drinking, withdrawal can be medically serious. If you experience tremors, rapid heartbeat, confusion, or seizures after stopping alcohol, those need to be managed first, sometimes with medical supervision or medication specifically for withdrawal. Naltrexone is not a detox drug. It’s meant to start after detox is complete.
Opioid Use Changes the Timeline
If you’ve recently used any opioid, whether a prescription painkiller, heroin, or medication like methadone, the timeline shifts significantly. Naltrexone blocks opioid receptors, and taking it while opioids are still in your system can trigger sudden, severe withdrawal. For short-acting opioids, you typically need to be opioid-free for at least 7 to 10 days. For long-acting opioids like methadone, that window can extend to 10 to 14 days or longer. This is one of the most important safety considerations, and your prescriber will likely verify opioid-free status before writing the prescription.
Medical Tests Before Your First Dose
Before starting naltrexone, you’ll need a liver function test. Naltrexone is processed by the liver, and it’s contraindicated in people with acute hepatitis or liver failure. The threshold that typically disqualifies someone is liver enzyme levels greater than five times the upper limit of normal. In a large clinical trial of over 1,300 participants, fewer than 1% had elevations that high, so most people with alcohol use disorder can safely take it, but the test is still standard practice because heavy drinking commonly affects liver health.
How the First Dose Works
You don’t jump straight to the full dose. The standard approach is to start with 25 mg on day one, then wait about an hour to confirm you don’t experience withdrawal symptoms or an unusually strong reaction. If that first half-dose goes well, you move to the full 50 mg dose the next day. This is the standard maintenance dose for most people: 50 mg once daily, taken by mouth.
Some prescribers use alternative schedules, such as 100 mg every other day or 150 mg every third day, which can work for people who prefer less frequent dosing. There’s also a monthly injectable form (380 mg) for people who find it difficult to take a daily pill consistently.
What to Expect in the First Week
The most common early side effect is nausea, which is why the gradual dose increase matters. Other effects during the first week or two can include headache, dizziness, sleepiness, trouble sleeping, decreased appetite, joint pain, and muscle cramps. Some people report cold-like symptoms. These effects are generally mild and tend to fade as your body adjusts. Taking naltrexone with food can help reduce nausea.
What naltrexone does functionally is block the receptors in your brain that respond to opioids, which are also involved in the pleasurable effects of alcohol. When those receptors are blocked, drinking becomes less rewarding. You may still want a drink out of habit, but the buzz feels muted or absent. Over time, this can weaken the learned association between drinking and pleasure, making it easier to cut back or stop.
How Long Treatment Lasts
Plan for a minimum of 3 to 4 months. That’s the duration supported by clinical trial data showing meaningful reductions in heavy drinking. However, many people relapse within months to a year after stopping the medication, so longer courses are common. Some people stay on naltrexone for a year or more, especially if they’re doing well and tolerating it without issues. Your prescriber will likely schedule monthly check-ins during treatment, including repeat liver function tests, to monitor how things are going.
The medication works best when combined with some form of counseling or behavioral support. Naltrexone reduces the biological pull of alcohol, but the habits, triggers, and emotional patterns around drinking typically need their own attention. The combination of medication and therapy consistently outperforms either approach alone.
Starting Without Full Abstinence
Some clinicians prescribe naltrexone using what’s known as a targeted approach, where you take it about an hour before you expect to drink rather than every day. The idea is that blocking opioid receptors during drinking sessions gradually reduces the reinforcement you get from alcohol. This approach can appeal to people who aren’t ready for full abstinence or who want to reduce their drinking rather than quit entirely. It’s not the FDA-approved protocol, and the evidence base is smaller, but some practitioners use it in clinical settings. If this sounds more realistic for your situation, it’s worth discussing with a prescriber who’s familiar with it.