NaltrexoneNaltrexone Hydrochloride

About Naltrexone

Naltrexone is a pure opioid antagonist that blocks the effects of opioids; how it helps in alcohol dependence is not understood. Tablets are labeled for alcohol dependence and for blocking the effects of opioids a person takes; Vivitrol is labeled for alcohol dependence in people who can stop drinking as outpatients before it starts, and for preventing relapse to opioid dependence after detoxification, as part of a program with psychosocial support. For alcohol dependence the tablet dose is 50 mg once a day; to block opioids, treatment starts at 25 mg and continues at 50 mg a day if no withdrawal appears, and supervised schedules such as 100 mg every other day or 150 mg every third day may be used. Vivitrol is 380 mg injected deep into a buttock muscle by a healthcare provider every 4 weeks or once a month. Safety in children has not been established for either form.

Naltrexone has no boxed warning. It must not be used by people taking opioid pain medicines, dependent on opioids (including people maintained on methadone or buprenorphine), in opioid withdrawal, who fail a naloxone challenge test or have a positive opioid urine screen, or who are allergic to it. Taking it with opioids still in the body can bring on sudden withdrawal, sometimes severe enough to need hospital care, so the labels recommend at least 7 to 10 days without opioids after dependence on short-acting opioids, and people switching from buprenorphine or methadone can be vulnerable for as long as two weeks. Because tolerance falls, an opioid dose once taken safely can be fatal after treatment stops, near the end of a Vivitrol dosing month or after a missed dose, and trying to overcome the blockade is especially dangerous; the Vivitrol label asks prescribers to strongly consider naloxone or nalmefene. Other warnings cover liver injury and depression or suicidal thinking and, for Vivitrol, injection site reactions (some needing surgery), eosinophilic pneumonia and allergic reactions. In a safety study in alcohol dependence, nausea and headache were the most common new side effects of the tablets.

Naltrexone does not cause physical or psychological dependence and is not a controlled substance, so tablet prescriptions can carry refills. Vivitrol’s label was updated in December 2025 on access to an overdose reversal agent, and naloxone 4 mg nasal spray is sold without a prescription. The ReVia brand of the tablets is discontinued. Very low doses, sometimes called low-dose naltrexone, are not an FDA-approved use, and compounded drugs are not FDA-approved.

Taking Naltrexone

How to take it

Tablets: once a day with or without food, or on a supervised clinic schedule such as every other day or every third day, starting only after the opioid-free period the prescriber sets. Injection: given into a buttock muscle by a healthcare provider every 4 weeks, alternating sides; it is never self-injected. Carry identification saying you take naltrexone.

If you miss a dose

Tablets: take it as soon as you remember, unless the next dose is almost due; then skip it, and never take a double dose. Injection: schedule another appointment as soon as possible, since sensitivity to opioids rises after a missed dose.

Storage

Tablets at room temperature in a tightly closed container, out of reach of children; do not flush them, but use a take-back program. The injection kit is refrigerated and never frozen, and it can be kept unrefrigerated at no more than 77°F for up to 7 days.

Interactions to know about

It blocks opioid medicines for pain, cough, colds and diarrhea, and taking large opioid doses to overcome it can cause a fatal overdose. Thioridazine with it has caused lethargy and sleepiness, and combining it with disulfiram, which can also harm the liver, is not ordinarily recommended. Tell any doctor or dentist that you take it.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Naltrexone differs from pharmacy to pharmacy

Any rated generic 50 mg tablet can fill a tablet prescription; the 25 and 100 mg tablets have no equivalence rating. Each pharmacy sets its own cash price, including its dispensing fee.

The injection has no rated generic on sale, so it is supplied as Vivitrol or as the unbranded version made under the same approval, each a refrigerated single-dose kit given by a healthcare provider.

Ways to pay less for Naltrexone without insurance

• Ask whether naltrexone 50 mg tablets are on the pharmacy’s flat-price generic list, and compare more than one pharmacy.
• Once your dose is settled, ask for a ninety-day supply with refills; naltrexone is not controlled.
• For the injection, ask whether the unbranded version can be supplied, and whether the maker’s savings or patient assistance program applies to someone paying cash; many copay cards require commercial insurance.
• Ask the prescriber whether daily generic tablets could suit you instead of the monthly injection.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Naltrexone

1. 1.How long must I be free of opioids, including buprenorphine or methadone, before my first dose?
2. 2.Which pain, cough, cold or diarrhea medicines will it block?
3. 3.Should I keep naloxone or nalmefene at home, and where can I get it?
4. 4.Which liver or mood symptoms should I report right away?

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