Vivitrol and naltrexone are the same drug. Vivitrol is the brand name for an extended-release injectable form of naltrexone, given once a month as a shot in the gluteal muscle. Naltrexone also comes as a daily oral tablet sold under generic labels. The active compound is identical in both, but the way it enters your body and how long it lasts differ significantly.
Same Drug, Different Delivery
Naltrexone works by blocking opioid receptors in the brain, primarily the mu-opioid receptor. This does two things: it prevents opioids from producing a high if someone uses them, and it reduces the reinforcing “reward” signal that drives cravings for both opioids and alcohol. An active metabolite of naltrexone also contributes to this blocking effect, and the drug influences hormonal pathways involved in alcohol consumption.
The oral tablet is taken once a day. It absorbs quickly, reaching peak blood levels about four hours after you swallow it, and has a half-life of roughly 10 hours. Its bioavailability is less than 50%, meaning more than half the dose is broken down by the liver before it ever reaches the bloodstream. Blood levels can fluctuate quite a bit from dose to dose.
Vivitrol solves this problem with a different delivery system. The injection contains tiny polymer microspheres that dissolve slowly in muscle tissue, releasing naltrexone steadily over about 30 days. Blood concentrations stay relatively stable within one to three days of the injection and don’t vary much throughout the month. That consistent drug level is a meaningful clinical advantage over the daily pill’s peaks and valleys.
What Each Formulation Treats
Both formulations are FDA-approved for treating alcohol use disorder and for preventing relapse to opioid dependence after detoxification. Neither version is a standalone treatment. Both are intended to be part of a broader program that includes counseling or other psychosocial support.
One important requirement applies to both: if you’ve been using opioids, you need to be completely opioid-free for a minimum of 7 to 10 days before starting naltrexone in any form. Starting too soon can trigger precipitated withdrawal, a sudden and intense withdrawal reaction caused by the drug rapidly displacing opioids from your receptors.
Why the Injection Often Works Better in Practice
The biggest real-world difference between oral naltrexone and Vivitrol comes down to whether people actually keep taking it. A daily pill is easy to skip, especially on days when cravings are strong or motivation dips. In a study published in JAMA Internal Medicine comparing the two in hospitalized patients with alcohol use disorder, only 26.6% of patients assigned to oral naltrexone maintained high adherence, compared with 40.7% in the injectable group. That gap matters because naltrexone only works while it’s in your system.
With Vivitrol, a single clinic visit covers an entire month of treatment. You can’t forget a dose or impulsively decide to stop taking it on a difficult day. For many people, that built-in consistency is the reason their provider recommends the injection over the pill.
Side Effects: Shared and Unique
Because the active drug is the same, most side effects overlap between the two formulations. Both can cause nausea, vomiting, headache, dizziness, fatigue, decreased appetite, and abdominal pain.
The injection adds one category of side effects that the pill does not: reactions at the injection site. Some pain and tenderness after the shot are normal and typically resolve within a few days. A small lump at the site is common and usually goes away over two to four weeks. More serious reactions, though less frequent, have been documented. The FDA issued an alert noting 196 reports of injection-site problems including cellulitis, abscess, and tissue death, 16 of which required surgical treatment. These serious reactions most often happen when the medication is accidentally injected into the fat layer under the skin instead of deep into the muscle.
If a reaction at the injection site becomes painful, red, and swollen and doesn’t improve within one to two weeks, that warrants prompt medical attention. Most reactions appear within one to three days of the shot. Notably, when patients who react to the injection switch to the oral tablet, they generally do fine, which confirms that the problem is the delivery mechanism rather than the naltrexone itself.
Practical Differences to Consider
Oral naltrexone is available as a generic, making it considerably cheaper. You fill a prescription at any pharmacy and take it at home. This gives you flexibility: you can adjust timing, and if side effects are bothersome, you simply stop taking it and the drug clears your system within a day or two.
Vivitrol requires a clinic visit for each monthly injection and has specific storage requirements. The dose pack must be refrigerated between 2°C and 8°C (36°F to 46°F). It can sit at room temperature for up to seven days before administration, but it cannot be frozen or exposed to temperatures above 25°C (77°F). These logistics mean your provider’s office needs to stock it properly, and appointments need to be scheduled in advance.
The tradeoff is straightforward. The pill offers convenience, lower cost, and the ability to stop easily. The injection offers steady drug levels, dramatically better adherence, and no daily decision-making about whether to take your medication. For someone whose primary challenge is staying consistent with treatment, that monthly shot can be the difference between staying on track and quietly drifting away from recovery.