Medicines & Supplements A to Z > Naltrexone


Last updated on 03/08/2021.

Overview   |   Dosage   |    Side Effects   |   Precautions  |   Tips  |   Where To Buy  

GENERIC NAME: Naltrexone



DRUG CLASS: Drugs in substance dependence

SUB CLASS: Opioid antagonist

USED FOR: Opioid dependence, Alcoholism


What is Naltrexone for?

Naltrexone belongs to a class of medications called opioid antagonists. It is used in the treatment of opioid and alcohol dependence.

How to use it?

Naltrexone is taken orally as tablets. Listed below are the indications and dosages. 

For alcoholism:
50 mg once daily.

For opioid dependence:
Initiate 25 mg once daily. If no withdrawal signs occur, administer 50 mg once daily thereafter.

What are the side effects of Naltrexone?

Common side effects of Naltrexone include nausea, loss of appetite, diarrhea, constipation, muscle pains, and difficulty sleeping.

Who should not take Naltrexone?

– People who are allergic to Naltrexone or any component of the formulation
– Patients currently taking any opioids, including opioid analgesics, Methadone, or Buprenorphine
– Patients in acute opioid withdrawal
– Patients who have failed the Naloxone challenge test or who have a positive urine screen for opioids

Pharmacist Tips:

– It is important to have good adherence to enhance treatment efficacy.
– Do not drink alcohol during treatment.
– Do not drive or operate machinery until you know the effect of the medicine.
– You should be off all opioids for a minimum of 7-10 days before starting Naltrexone in order to avoid precipitation of opioid withdrawal. Then, a Naloxone challenge test would be done to ensure you have an adequate opioid-free period.
– You might be more sensitive to opioid drugs after the treatment, so there is a higher risk for accidental opioid overdose even when using opioids of lower doses or previously tolerated doses.
– This drug may cause serious liver problems. Report any symptoms immediately such as fatigue, abdominal pain, loss of appetite, itching, bruising, and yellow skin or eyes. 

Common dosing schedule:
Naltrexone can be taken with or without food. 

This schedule is for reference only, adjustments may be made according to individual needs.

Some common medications Naltrexone may interact with:
– Opioids analgesics, e.g. Morphine, Codeine, Tramadol

Please notify your doctor or pharmacist if you are taking the above medication, dosage adjustments might be needed.

Where to buy Naltrexone in Hong Kong?

In Hong Kong, Naltrexone is a prescription only medicine, and requires a prescription from a doctor to be purchased in a pharmacy. It can also be obtained from doctors. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.

For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at

Need more information?

For detailed information about the use of Naltrexone in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.

Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.