Medication Information Leaflet

What is this medication for?

Naltrexone is used to help people stay off heroin or other opioids after having been weaned off from them.

It can also be used to help you reduce the desire to drink alcohol.

Naltrexone may be used for other conditions. Check with your healthcare professional if you are unsure why you are given this medication.

How should I take/use this medication?

  • Naltrexone should be taken with or after food.
  • Take your medication according to the instructions stated on the medication label.
  • Do not stop taking or adjust the dose of this medication without checking with your doctor.
  • Do check with your doctor on how long you will have to be on this medication.

Do not give your tablets to people who are dependent on opioids as they could cause life-threatening withdrawal symptoms. If this happens, call 995 at once.

IMPORTANT: Do not take Naltrexone if you have taken heroin or other opioids in the past 7-10 days.

Doing so may result in unpleasant, and sometimes severe withdrawal symptoms within minutes of taking naltrexone. Withdrawal symptoms include:

  • Stuffy or runny nose
  • Teary eyes
  • Tiredness
  • Sweating
  • Anxiety
  • Tremors
  • Nausea, vomiting and abdominal cramps
  • Bone pain or muscle aches
  • Diarrhoea

Be sure that your family or caregiver are also aware of the above symptoms so they can call your doctor if you are unable to seek treatment on your own.

What should I do if I forget to take/use this medication?

  • If you forget to take a dose, take it as soon as you remember. However, if more than half of the time to the next dose has passed, skip the missed dose and take the next dose at your usual timing.
  • For example, for a medication to be taken two times daily at 8am and 8pm, and you missed your first dose at 8am, skip the first dose if it is after 2pm, and take your second dose at the usual timing at 8pm. Do not take two doses to make up for the missed dose.
  • Do not take heroin or other opioids once you have stopped or skipped your dose. Naltrexone blocks the “high” feeling you get from heroin and other opioids. Do not try to overcome the effect of Naltrexone by using higher doses of heroin or other opioids, as this can result in breathing difficulties and even death from overdose.

What precautions should I take?

Inform your healthcare professional if:

  • You are allergic to this medication or any of the other ingredients of this medication.
  • You are pregnant, planning to become pregnant, or breastfeeding. If you are pregnant and/or breastfeeding, your doctor would have discussed the potential benefits and side-effects with you and should you have further questions or concerns, do consult your doctor.
  • You are taking any other medications (including those that can be bought without a prescription), supplements, traditional Chinese medicine and herbal products. Some of them may affect how this medication works or cause serious drug interactions.
  • You have or have ever had:
    • Other drug allergies
    • Kidney or liver disease
    • Previous thoughts or attempts to end your life, with or without depression
    • Pain-killers use
    • Drug addiction or signs of withdrawal

Carry an identification card stating that you are taking naltrexone. This serves as an alert to medical personnel in the event of an emergency.

What are some common side-effects of this medication?

The mentioned side effects generally affect up to 10% of patients.

  • Drowsiness or feeling tired
    • Avoid driving or taking part in activities that require concentration
    • Discuss with your doctor if you can take your medication at a different time of the day
  • Nausea or vomiting, loss of appetite, stomach discomfort
    • Take the medication with or after food
    • Take small but more frequent meals, and avoid fatty or spicy food
  • Constipation
    • Drink more water (if you do not have any fluid restriction), eat more high-fibre foods, and exercise regularly
    • Speak to your doctor or pharmacist if you need medication to help with your constipation
  • Dizziness
    • Get up slowly from a sitting or lying down position
  • Difficulty sleeping
    • Discuss with your doctor if you can take your medication at a different time of the day
    • Listen to relaxing music at bedtime
    • Avoid eating or drinking too much before bedtime
    • Limit your caffeine intake (such as coffee, tea or energy drinks) at least 8 hours before bedtime
  • Headache, joint or muscle pain
  • Feeling anxious or irritable

Most of the side effects listed here will improve with time. Speak with your doctor if any of them continues, worsens or affects your daily life.

What are some rare but serious side-effects that I need to seek medical advice immediately?

The symptoms of a drug allergy include one or more of the following:

  • Swollen face/eyes/lips/tongue
  • Difficulty in breathing
  • Itchy skin rashes over your whole body

Rarely this medication may cause:

  • Loss of appetite, severe nausea or vomiting, pain in the upper part of the stomach, yellowing of the skin or ‘whites’ of the eyes, dark-brown coloured urine and/or pale/clay-coloured stools (signs and symptoms of liver problem)

If you experience any of these symptoms, you should stop your medication and see your healthcare professional immediately.

What food or medication should I avoid when I take this medication?

Avoid drinking alcohol while taking Naltrexone.

Do not take heroin or other opioids while taking Naltrexone. Naltrexone blocks the “high” feeling you get from these drugs. Any attempts to overcome the effect of naltrexone by consuming higher doses of the drugs may lead to an opioid overdose.

Avoid taking opioid-based medications such as certain anti-diarrhoeal preparations, codeine-based cough medications or strong pain-killers.

How should I store this medication?

Store in a cool and dry place, away from direct sunlight. Keep this medication away from children.

How should I throw away this medication safely?

Pack this medication into a trash bag and seal it tightly before throwing into the rubbish chute or bin.


Please take note that the above is not a complete list of all possible side effects. If you have any concerns about your medication or if you have other side effects that you think are caused by this medication, please consult your doctor or pharmacist.

If you take more than the recommended dose, please seek medical advice immediately. The information provided on this page does not replace information from your healthcare professional. Please consult your healthcare professional for more information.

This article is jointly developed by members of the National Medication Information workgroup. The workgroup consists of cluster partners (National Healthcare Group, National University Health System and SingHealth), community pharmacies (Guardian, Unity and Watsons) and Pharmaceutical Society of Singapore. The content does not reflect drug availability and supply information in pharmacies and healthcare institutions. You are advised to check with the respective institutions for such information.

Last updated on Mar 2023

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