Substance guides

Naloxone vs. naltrexone: Understanding the difference

Published January 15, 2025 · 6 min read · Updated April 2026

Reviewed for accuracy by licensed clinical professionals.

Naloxone and naltrexone are both opioid antagonists but serve completely different purposes. Confusing them is common and potentially dangerous.

Naloxone (Narcan)

Emergency overdose reversal. Works within 2-5 minutes. Lasts 30-90 minutes. Given during overdose only. Available OTC as nasal spray. No ongoing use.

Naltrexone (Vivitrol, ReVia)

Long-term relapse prevention. Blocks opioid effects and reduces alcohol cravings. Taken daily (oral) or monthly (injection). Used as ongoing MAT. Requires being opioid-free before starting.

Key differences

Naloxone: emergency rescue medication. Naltrexone: daily or monthly maintenance medication. Naloxone: given TO someone overdosing. Naltrexone: taken BY the person in recovery. Both block opioid receptors but in different clinical contexts.

Authoritative sources

This article references guidelines from: SAMHSA · NIDA · ASAM

Frequently asked questions

Is naloxone the same as naltrexone?

No. Naloxone reverses active overdose (emergency use). Naltrexone prevents relapse (ongoing treatment). Both block opioid receptors but serve different purposes.

Can naltrexone reverse an overdose?

Naltrexone blocks opioids but is not used for emergency overdose reversal. Naloxone (Narcan) is the emergency medication.

Do I need both naloxone and naltrexone?

They serve different purposes. Naltrexone is ongoing treatment. Naloxone is emergency rescue. You may use naltrexone for treatment while keeping naloxone available for others.

Disclaimer: Informational only. Not medical advice. SAMHSA: 1-800-662-4357.