Naltrexone is administered in two FDA-approved forms: a daily oral tablet (50 mg) and a monthly extended-release injection (380 mg, sold as Vivitrol). The form you receive depends on the condition being treated, your treatment history, and how well you’re likely to stick with a daily pill. Both forms are used for alcohol use disorder and opioid use disorder, though they come with different preparation requirements, costs, and practical considerations.
Oral Tablets
The standard oral dose is 50 mg once a day. If you’re starting naltrexone for opioid use disorder, your provider will typically begin with a half tablet (25 mg) on the first day to see how you respond. If no withdrawal symptoms appear, you move to the full 50 mg dose the next day. For alcohol use disorder, most people start directly at 50 mg daily.
Oral naltrexone is relatively affordable. A 30-day supply of generic 50 mg tablets costs around $128 at wholesale pricing, though your actual cost will vary with insurance. The tradeoff is that you need to remember to take it every day, and adherence is one of the biggest challenges with this form. People dealing with active substance use disorders often struggle with daily medication routines, which is one reason the injectable version was developed.
Monthly Injection (Vivitrol)
The extended-release injectable form delivers 380 mg of naltrexone as a single intramuscular shot once every four weeks. A healthcare provider administers it into the upper outer quadrant of the gluteal muscle (the buttock), alternating sides with each monthly visit. You cannot give yourself this injection at home.
The injection kit comes with customized needles in two lengths: 1.5 inches and 2 inches. Before each injection, the provider assesses which needle length is appropriate based on your body type, since the medication must reach deep into the muscle tissue to work correctly. It cannot be given intravenously or under the skin. The provider mixes the medication from a vial of microspheres and a diluent immediately before injecting.
The major advantage of the injection is that it removes the daily decision to take a pill. Once it’s in, the medication works steadily for a full month. The major disadvantage is cost: a single injection runs roughly $1,570 at wholesale, more than 12 times the price of a month of oral tablets.
What Happens Before You Start
If you’re being treated for opioid use disorder, you must be completely opioid-free for at least 7 to 10 days before your first dose of naltrexone in any form. This includes all opioids: prescription painkillers, heroin, methadone, buprenorphine, and tramadol. Taking naltrexone while opioids are still in your system triggers precipitated withdrawal, a sudden and intense version of opioid withdrawal that can be severe.
To verify you’re ready, your provider may perform a naloxone challenge test. This involves giving you a small dose of naloxone, a short-acting opioid blocker, and watching for withdrawal symptoms over 20 to 30 minutes. If nothing happens, your body is clear enough to start naltrexone safely. A negative result on this test doesn’t guarantee zero risk, but it significantly reduces the chance of a bad reaction. If withdrawal symptoms do appear during the challenge, your provider will treat them and either retry in 24 hours or discuss alternative treatment options.
For alcohol use disorder, this opioid washout period isn’t required, but your provider will still want to assess your liver function and overall health before starting treatment.
Low-Dose Naltrexone (Off-Label Use)
You may have heard about low-dose naltrexone, commonly called LDN, which is an off-label use of the same medication at much smaller doses. Where the standard dose is 50 mg, LDN typically ranges from 0.1 mg to 4.5 mg per day. It’s used primarily for chronic pain conditions, though it’s prescribed for a variety of inflammatory and autoimmune issues as well.
LDN is taken orally, usually as a compounded capsule or liquid since commercial tablets aren’t manufactured at these tiny doses. Many providers use a slow titration approach, starting at 0.1 mg per day and increasing by 0.1 mg every three days until an effective dose is found. Research suggests most people find relief at 2 mg or less per day, which challenges the common practice of jumping straight to 4.5 mg.
Timing matters with LDN. If it causes vivid dreams or trouble falling asleep, taking the last dose no later than 4 PM (or shifting the entire dose to the morning) often helps. If it causes stomach discomfort, taking it with food usually resolves the issue. Some people split their daily dose across two or three smaller doses throughout the day for better tolerability.
Implants Are Still Investigational
Researchers are testing a subcutaneous implant called iSTEP-N that would deliver naltrexone continuously from a biodegradable material placed under the skin. The goal is to extend the treatment window beyond the current one-month injection cycle, reducing the number of clinic visits needed. This product is still in Phase 1 clinical trials comparing its blood levels to those achieved by Vivitrol. It is not FDA-approved and is not currently available outside of research settings.