Class Name(s):

• 28:10 Opioid Antagonists

Pronunciation:

• (nal trex' one)

Brand Name(s):

• Vivitrol^®

WHY is this medicine prescribed?

Naltrexone injection is used along with counseling and social support to help people who have stopped drinking alcohol and using opioids. Naltrexone is in a class of medications called opiate antagonists. It works by decreasing the craving for alcohol and blocking the effects of opioids.

HOW should this medicine be used?

Naltrexone injection comes as a solution (liquid) to be given by injection into the muscle of the buttocks by a healthcare provider once every 4 weeks.

To achieve the best possible treatment outcome, naltrexone injection is used as part of an addiction treatment program. It is important that you attend all counseling sessions, support group meetings, education programs, or other treatments recommended by your doctor.

Naltrexone injection will help you avoid using opioids and alcohol, but it will not prevent or relieve the withdrawal symptoms that may occur when you stop using these substances. Instead, naltrexone injection may cause or worsen withdrawal symptoms. You should not take naltrexone injection if you have recently stopped using opioid medications or opioid street drugs and are now experiencing withdrawal symptoms.

Naltrexone will help you avoid drugs and alcohol only as long as you are using it. Continue to see your healthcare provider for your naltrexone injection even if you feel well. Do not stop seeing your healthcare provider for your naltrexone injection without talking to your doctor.

Are there OTHER USES for this medication?

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

What SPECIAL PRECAUTIONS should I follow?

Before receiving naltrexone injection,

• tell your doctor and pharmacist if you are allergic to this medication, any part of this medication, or any other medications, foods or substances. Tell your doctor or pharmacist about the allergy and what symptoms you had.
• tell your doctor if you have taken any opiate medications including certain medications for diarrhea, cough, or pain; methadone; or buprenorphine within the last 7 to 10 days or if you are withdrawing from opioids. Ask your doctor if you are not sure if a medication you have taken is an opiate Also tell your doctor if you have used any opiate street drugs such as heroin within the last 7 to 10 days. Your doctor may order certain tests to see if you have recently taken any opiate medications or used street drugs. Your doctor will not give you naltrexone injection if you have recently taken an opiate medication or used street drugs.
• you should know that you should not take any opiate medications or use opioid street drugs during your treatment with naltrexone injection. Naltrexone injection blocks the effects of opiate medications and opioid street drugs. You may not feel the effects of these substances if you take or use them at low or normal doses. If you take or use higher doses of opioid medications or street drugs during your treatment with naltrexone, it may cause serious injury, coma (long-lasting unconscious state), or death.
• you should know that if you took opioid medications before your treatment with naltrexone, you may be more sensitive to the effects of these medications after you finish your treatment. After you finish your treatment, tell any doctor who may prescribe medication for you that you were previously treated with naltrexone injection.
• you should know that some medications should not be taken with naltrexone injection. Other medications may cause dosing changes or extra monitoring when taken with naltrexone injection. Make sure you have discussed any medications you are currently taking or plan to take before starting naltrexone injection with your doctor and pharmacist. Before starting, stopping, or changing any medications while taking naltrexone injection, please get the advice of your doctor or pharmacist.
• tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take.
• tell your doctor if you have ever had depression, suicidal thoughts or behaviors, bleeding problems such as hemophilia (a bleeding disorder in which the blood does not clot normally), a low number of platelets in your blood, depression, or kidney or liver disease.
• tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while receiving naltrexone injection, call your doctor.
• if you need medical treatment or surgery, including dental surgery, tell the doctor or dentist that you are receiving naltrexone injection. Wear or carry medical identification so that healthcare providers who treat you in an emergency will know that you are receiving naltrexone injection.
• you should know that naltrexone injection may make you feel dizzy or drowsy. Do not drive a car or operate machinery or do other dangerous activities until you know how this medication affects you.
• you should know that people who overuse drugs or alcohol can become depressed and sometimes try to harm or kill themselves. Receiving naltrexone injection does not decrease the risk that you will try to harm yourself. You, your family, or your caregiver should call your doctor right away if you experience symptoms such as feelings of sadness, anxiousness, worthlessness, or helplessness, or thinking about harming or killing yourself or planning or trying to do so. Be sure that your family or caregiver knows which symptoms may be serious so they can call the doctor right away if you are unable to seek treatment on your own.
• talk to your doctor about the risks and benefits of naltrexone injection before you receive your first dose. Naltrexone will remain in your body for about 1 month after you receive the injection and cannot be removed before this time.

What SPECIAL DIETARY instructions should I follow?

Unless your doctor tells you otherwise, continue your normal diet.

What should I do IF I FORGET to take a dose?

If you miss an appointment to receive naltrexone injection, schedule another appointment as soon as possible.

What SIDE EFFECTS can this medicine cause?

Naltrexone injection may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• nausea, vomiting, diarrhea, stomach pain
• decreased appetite
• dry mouth
• headache
• difficulty falling asleep or staying asleep
• dizziness, tiredness, anxiety
• joint pain or stiffness
• muscle cramps
• weakness
• tenderness, redness, bruising, or itching at the injection site

Some side effects can be serious. If you experience any of these symptoms or those listed in the IMPORTANT WARNING section, call your doctor immediately or get emergency medical treatment:

• pain, hardness, swelling, lumps, blisters, open wounds, or a dark scab at the injection site
• excessive tiredness, unusual bleeding or bruising, pain in the upper right part of the stomach, light-colored bowel movements, dark urine, or yellowing of the skin or eyes
• coughing, wheezing, shortness of breath
• hives, rash, swelling of the eyes, face, mouth, lips, tongue, or throat
• chest pain
• thoughts of suicide or suicidal behaviors

Naltrexone injection may cause other side effects. Call your doctor if you have any unusual problems while receiving this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

What should I do in case of OVERDOSE?

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at http://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

Symptoms of overdose may include:

• nausea
• stomach pain
• drowsiness
• dizziness

What OTHER INFORMATION should I know?

Keep all appointments with your doctor and the laboratory.

Before having any laboratory test, tell your doctor and the laboratory personnel that you are receiving naltrexone injection.

Ask your doctor or pharmacist any questions you have about naltrexone injection.

Keep a written list of all of the prescription and nonprescription (over-the-counter) medicines, vitamins, minerals, and dietary supplements you are taking. Bring this list with you each time you visit a doctor or if you are admitted to the hospital. You should carry the list with you in case of emergencies.

This report on medications is for your information only, and is not considered individual patient advice. Because of the changing nature of drug information, please consult your physician or pharmacist about specific clinical use.

The American Society of Health-System Pharmacists, Inc. represents that the information provided hereunder was formulated with a reasonable standard of care, and in conformity with professional standards in the field. The American Society of Health-System Pharmacists, Inc. makes no representations or warranties, express or implied, including, but not limited to, any implied warranty of merchantability and/or fitness for a particular purpose, with respect to such information and specifically disclaims all such warranties. Users are advised that decisions regarding drug therapy are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and the information is provided for informational purposes only. The entire monograph for a drug should be reviewed for a thorough understanding of the drug's actions, uses and side effects. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information is not a substitute for medical care.

AHFS^® Patient Medication Information™ Copyright, 2026. The American Society of Health-System Pharmacists^®, 4500 East-West Highway, Suite 900, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

Selected Revisions: September 15, 2026.