Naltrexone comes in two forms: a daily oral tablet (50 mg) and a monthly injection (380 mg). How you use it depends on whether you’re treating alcohol use disorder, opioid use disorder, or following a specific protocol like the Sinclair Method. The basics are straightforward, but timing, preparation, and safety details matter.
How Naltrexone Works
Naltrexone blocks opioid receptors in your brain. These are the same receptors that produce the rewarding “buzz” from alcohol or the high from opioid drugs. When those receptors are blocked, drinking feels less pleasurable and cravings lose their grip. For opioid use disorder, the blockade means that using opioids produces little to no effect, removing a major incentive to relapse.
This mechanism makes naltrexone fundamentally different from medications that manage withdrawal symptoms. It doesn’t sedate you, it isn’t addictive, and it doesn’t produce a high. It simply dulls the reward signal that keeps the cycle going.
Oral Tablets for Alcohol Use Disorder
The standard oral dose is 50 mg once daily. Some prescribers use flexible schedules: 100 mg every other day or 150 mg every third day. Most people take it in the morning with food, which helps reduce nausea. You don’t need to be completely abstinent from alcohol before starting, though treatment should begin after acute withdrawal symptoms have cleared.
In clinical trials, naltrexone reduced heavy drinking days by about 17% compared to placebo and increased days of total abstinence. Those numbers may sound modest on paper, but over weeks and months, fewer heavy drinking days translates into significantly better health outcomes and a more stable recovery trajectory. Naltrexone works best when combined with some form of counseling or behavioral support, though the medication carries real benefit on its own.
Treatment duration varies. Many providers recommend at least three to six months, and some people stay on it for years. Long-term use has a solid safety profile, with side effects generally limited to headache, nausea, and abdominal discomfort.
The Sinclair Method
The Sinclair Method uses naltrexone differently from daily dosing. Instead of taking the pill every morning, you take 50 mg exactly one hour before you plan to drink alcohol. On days you don’t drink, you don’t take it.
The idea is pharmacological extinction: every time you drink with naltrexone on board, your brain receives less reward from alcohol. Over months, the learned association between alcohol and pleasure gradually weakens. Proponents report that drinking naturally decreases over time as the drive behind it fades. This approach requires discipline around timing. If you drink without having taken the pill an hour beforehand, you get the full reward signal, which can reinforce the habit rather than weaken it.
Using Naltrexone for Opioid Use Disorder
If you’re taking naltrexone for opioid use disorder, the preparation requirements are stricter. You must be completely free of all opioids for 7 to 10 days before your first dose. This includes prescription painkillers, heroin, and opioid-based medications used in other treatment programs. Starting naltrexone while opioids are still in your system triggers precipitated withdrawal, which is a sudden, intense onset of withdrawal symptoms far worse than what happens naturally.
The 7-to-10-day window is a significant hurdle. In clinical practice, this detox period is the hardest part of starting naltrexone for opioid use disorder, and it’s the main reason some people don’t complete the transition. Many treatment programs use a structured tapering protocol during the first week, followed by a washout period before the first naltrexone dose around day 15.
Once started, the oral dose is typically 50 mg daily, the same as for alcohol use disorder. The monthly injection is often preferred for opioid use disorder because it removes the daily decision to take a pill, which can be a point of vulnerability during early recovery.
The Monthly Injection
The injectable form delivers 380 mg of naltrexone into the gluteal muscle (the buttock) every four weeks. A healthcare provider administers it in a clinic. The injection site alternates between the left and right buttock each month, and needle length is adjusted based on body size to ensure the medication reaches deep muscle tissue.
The injection’s main advantage is adherence. You show up once a month and the medication works continuously. There’s no daily pill to forget or skip. This is especially valuable for opioid use disorder, where a single missed dose can open the door to relapse. For alcohol use disorder, it offers the same convenience, though some people prefer the flexibility of oral dosing.
You may notice soreness, redness, or a small lump at the injection site. These local reactions usually resolve within a few days. The same systemic side effects from oral naltrexone (nausea, headache, mild stomach discomfort) can occur with the injection as well.
Common Side Effects
Most people tolerate naltrexone well. In a study from an addiction treatment center, the most frequently reported side effects were dizziness (5% of patients), nausea (4.6%), and headache (2.7%). These tend to be mild and often improve after the first week or two. Taking the oral tablet with food reduces the chance of stomach-related symptoms.
Liver safety has historically been a concern, but current evidence is reassuring. Updated clinical guidance states that baseline liver function testing is not strictly necessary before starting treatment, as requiring it can delay care. Quarterly monitoring is generally sufficient, and testing should be prompted if you develop signs of liver problems like yellowing skin, persistent nausea, or abdominal pain. Studies in people with hepatitis C and HIV co-infection have not shown meaningful changes in liver function from naltrexone use.
Pain Management and Emergencies
Because naltrexone blocks opioid receptors, standard opioid pain medications will not work while you’re on it. This is critical to understand before surgery, dental procedures, or any situation requiring pain relief. If you need emergency care, your medical team must know you’re taking naltrexone so they can use non-opioid pain management or, if opioids are truly necessary, work with anesthesia specialists trained in overriding the blockade safely.
Carrying a medical alert card or wearing an alert bracelet is a practical step. Include your medication name, the prescribing provider’s contact information, and a note that opioid-based pain relief will be ineffective. This information can prevent dangerous situations where emergency providers attempt to push through the blockade with higher opioid doses, which risks respiratory complications once naltrexone wears off.
The oral tablet’s blocking effect lasts roughly 24 to 72 hours depending on dose. The monthly injection maintains its blockade for the full four-week period, with some residual effect beyond that. If you have a planned surgery, your provider can help you time the transition off naltrexone appropriately.