Naltrexone belongs to a group of medications known as pure opioid antagonists. It is used to help individuals who were previously dependent on drugs of addiction (such as alcohol, or opiate drugs such as methadone and heroin) to remain free from their dependence.

Opiate drugs (also known as opioid drugs) and opioids that are naturally part of the body affect certain parts of the brain called opiate receptors. Naltrexone works by binding to these opiate receptors to block the effects of opiates drugs and the body's own opiates. It is believed that this helps prevent a person from returning to using these substances.

This medication is used together with other forms of treatment such as psychological counselling and social support.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The dose of this medication depends on the type of dependence it is being used to treat, and whether administration of the medication will be supervised.

To treat alcoholism, the usual recommended dose is 50 mg once daily.

To treat opioid dependence (e.g., addiction to methadone or heroin), the dose will vary but the usual starting dose is 25 mg once daily, to be slowly increased to the most appropriate dose.

Your doctor will determine a dose and dosing schedule for your individual situation. It is important that you take this medication exactly as prescribed by your doctor.

Your doctor may request a urine sample before initiating treatment with this medication in order to make sure that you have not used any narcotics (opioid drugs) within the previous 7 to 10 days. You should not take this medication if there is any possibility that you have used an opiate within the previous 7 to 10 days. If there is any question about your opiate use, your doctor may request that you take a NARCAN challenge test in order to confirm that your body is opiate-free before you take this medication.

If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Each pale yellow, film-coated, capsule-shaped tablet, debossed with "R11" on one side and a scoring line and "50" on the other side, contains 50 mg of naltrexone hydrochloride. Nonmedicinal ingredients: colloidal anhydrous silica, crospovidone, lactose monohydrate, magnesium stearate, microcrystalline cellulose, and Pale Yellow Opadry® YS-1-6378-G (hypromellose, polyethylene glycol, polysorbate 80, red iron oxide, titanium dioxide, and yellow iron oxide).

Do not take naltrexone if you:

• are allergic to naltrexone or to any of the ingredients of the medication
• are dependent upon opiates, including if you are receiving opiate agonists (e.g., methadone)
• are experiencing opiate withdrawal
• are receiving opiate analgesics (e.g., narcotics medications such as oxycodone and codeine)
• have a urine test that is positive for opiates
• have acute hepatitis or liver failure
• have failed the NARCAN challenge (a test used to determine if you have used opiates)

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• abdominal pain or cramps
• anxiety
• chills
• constipation
• decreased libido
• delayed ejaculation
• diarrhea
• difficulty sleeping
• dry mouth
• fatigue
• feeling down
• headache
• increased energy
• increased thirst
• indigestion
• irritability
• joint and muscle pain
• loss of appetite
• low energy
• nausea
• nervousness
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• dizziness
• fainting
• skin rash
• symptoms of depression (e.g., low energy, feelings of worthlessness, guilt, helplessness or hopelessness)
• symptoms of narcotic withdrawal (e.g., tearfulness, nausea, abdominal cramps, restlessness, bone or joint pain, muscle pain, nasal irritation)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• attempts at suicide or thoughts of suicide
• signs of an allergic reaction (such as difficulty breathing, hives, skin rash, swelling of the face or throat)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.

Accidental ingestion: If you are dependent on narcotics and you accidentally ingest this medication, you could experience severe symptoms of withdrawal including confusion, nausea, shakiness, sweating, anxiety, visual hallucinations, vomiting, or diarrhea. Do not give this medication to anyone else, especially people who are dependent on opiate drugs.

Alcohol: You should not drink alcohol while taking this medication as this could damage your liver.

Interference with opiate-containing mediations: Because this medication works by blocking the effects of opiates, it may interfere with other medications that contain opiates such as certain cough and cold medications, antidiarrheal medications, and some analgesics (pain medications). Talk to your doctor or pharmacist about non-opiate containing alternatives.

Kidney function: If you have reduced kidney function your doctor may lower your dose of this medication. Your doctor may also request that you have regular kidney function tests while you are taking this medication.

Liver function: Naltrexone can cause liver injury. If you have reduced liver function your doctor may lower your dose of this medication. Your doctor may also request that you have regular liver function tests while you are taking this medication. If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Overdose: If you accidentally overdose on this medication, seek medical attention immediately.

Suicide: People with substance abuse problems are at a higher risk of suicide. The use of naltrexone does not lower this risk.

Taking opioid drugs: If you attempt to overcome the blocking effects of naltrexone by taking opiates, this may result in breathing difficulties and death. Do not take opiates while you are on this medication. Furthermore, you may be more sensitive to lower doses of opiates after treatment with naltrexone. A smaller dose than previously used may be required to achieve the same effect.

Treatment of alcohol dependence: The use of naltrexone for the treatment of alcohol dependence has only been studied for a dosage regimen of 50 mg once daily for up to 12 weeks. The efficacy of naltrexone beyond 12 weeks in this population is not known.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if naltrexone passes into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children less than 18 years of age.

There may be an interaction between naltrexone and any of the following:

• methylnaltrexone
• opiate-containing medications (e.g., codeine, morphine, oxycodone)
• naloxegol

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.