Treatment & Safety
Naltrexone Contraindications: Opioids, Withdrawal, and Label Checks
Current opioid use, opioid dependence, acute withdrawal, specified test results, and prior hypersensitivity can make naltrexone unsafe to start.
Dr Leonard Leng
Family physician, Singapore. External medical reviewer
Dr Leonard Leng is a family physician at ATA Medical in Singapore. He studied medicine (MBBS) at the National University of Singapore, then took a Graduate Diploma and a Master of Medicine in Family Medicine there. The Family Physicians Accreditation Board under Singapore’s Ministry of Health accredits him as a registered Family Physician. He also holds the NUS Graduate Diploma in Occupational Medicine and works as a Designated Workplace Doctor.
His clinical training covered internal medicine, emergency medicine, general surgery, orthopaedics, sports medicine and paediatrics. The American College of Lifestyle Medicine board-certified him in lifestyle medicine, and he is a founding member and vice-president of the Singaporean Society of Lifestyle Medicine.
Dr Leng is an external medical reviewer for Get Naltrexone. Peter Dunk writes and edits the articles, and Dr Leng checks them. You will see his name and the review date on each article he has reviewed, and the list below links to every one.
Check his credentials: Singaporean Society of Lifestyle Medicine directory, ATA Medical profile, LinkedIn.
Articles
Treatment & SafetyStarting Naltrexone After Opioids: Why the Opioid-Free Interval Matters
Naltrexone can trigger severe withdrawal if opioids are still present. The minimum interval is not a self-assessment rule and may be longer after buprenorphine or methadone.
Treatment & SafetyNaltrexone Side Effects: Expected Effects and Urgent Safety Signals
Nausea, headache, dizziness, and tiredness are reported with naltrexone. Vivitrol also has injection-site effects; certain symptoms need prompt clinical review.
Treatment & SafetyVivitrol Injection Administration: What Patients Should Know
Vivitrol is prepared and given only by a healthcare provider as a deep gluteal injection. This guide explains the patient-facing safety essentials.
Access by CountryAustralia Naltrexone PBS Check: Item 8370M and 2026 Co-payments
PBS item 8370M covers naltrexone 50 mg tablets; 2026 maximum co-payments are $25 general and $7.70 concession.
Treatment & SafetyNaltrexone and Liver Disease: What Current Evidence Shows
Observational studies are reassuring in many patients with liver disease and cirrhosis, but they do not make naltrexone risk-free or settle every decompensated-liver scenario.
Access by CountryNew Zealand Naltrexone Funding: June 2026 PHARMAC Check
A dated June 2026 check: Naltraccord 50 mg was fully subsidised under SA1408, with pharmacy charges and GP fees separate. Updated for the brand change of 1 November 2026.
Treatment & SafetyNaltrexone During Pregnancy and Breastfeeding: What We Know
Human pregnancy evidence remains limited; breastfeeding transfer appears low in one published case. Decisions require individual specialist assessment.
Access by CountrySingapore Naltrexone Check: Contrave Is Registered—What About 50 mg?
Singapore's official formulary confirms Contrave, while current standalone 50 mg naltrexone supply and price remain unverified.
Access by CountryUAE Naltrexone Registry Check: What Is Actually Listed?
A dated check of the UAE drug directory: Contrave is active, standalone naltrexone was not found, and DHA guidance still recognises naltrexone clinically.
Treatment EvidenceNaltrexone vs Acamprosate and Disulfiram
Naltrexone, acamprosate, and disulfiram have different goals, contraindications, and evidence. There is no universal best medicine.
Treatment EvidenceDoes Naltrexone Help With Weight Loss? Contrave Evidence
Standalone naltrexone is not an approved weight-management medicine. This evidence review examines Contrave—the naltrexone-bupropion combination—alongside its safety limits.
Treatment EvidenceTargeted Naltrexone in Asia-Pacific: What Access Evidence Shows
Targeted naltrexone has trial evidence, but local access depends first on whether standalone naltrexone is marketed and whether a clinician supports the protocol.