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General information only, not medical advice. In a suspected overdose call 911 first.
Naloxone works by attaching to opioid receptors and blocking the effects of opioids, which reverses an opioid overdose. Its effect is short, so an overdose can return after it wears off. That is why emergency help is still needed after naloxone has been used. This guide explains the mechanism, how long it lasts, and what it does not do, based on CDC, NIDA and FDA pages (checked 2026-11-04).
What is naloxone?
Naloxone is a medication that can reverse an overdose from opioids, including fentanyl, heroin and prescription opioids (CDC, “Lifesaving Naloxone”, page dated June 11, 2025). FDA describes it as a medication that rapidly reverses the effects of opioid overdose. NIDA lists two FDA-approved forms: an injectable and a prepackaged nasal spray. For the product itself, see what Narcan is and the types of naloxone nasal spray.
How does naloxone work in the body?
Naloxone attaches to opioid receptors and reverses and blocks the effects of other opioids (NIDA DrugFacts: Naloxone, January 2022). CDC puts it the same way: it quickly reverses an overdose by blocking the effects of opioids.
NIDA also states that naloxone has no effect on someone who does not have opioids in their system.
How long does naloxone last?
NIDA states that naloxone works to reverse an opioid overdose in the body for only 30 to 90 minutes. Because opioids can last longer than that, an overdose can return after the naloxone effect fades. This is why NIDA says people should still call 911 immediately in the event of an overdose.
| Point | What the source says | Source |
|---|---|---|
| Duration of naloxone action | 30 to 90 minutes | NIDA |
| Why the overdose can return | Opioids can last longer than naloxone | NIDA |
| Emergency services | Call 911; do not hesitate | CDC, NIDA |
What is naloxone used for?
It is used to reverse an overdose caused by opioids (CDC). CDC also says naloxone will not harm someone who is overdosing on drugs other than opioids.
How to give naloxone: where the instructions come from
This guide does not give step-by-step directions. Each naloxone product comes with its own instructions, and a 911 dispatcher can guide a caller. NIDA notes only that the nasal spray is prepackaged. For what a naloxone kit holds and how it is stored and restocked, see the Narcan kit contents and restocking guide, and for the wider supply context the emergency medication kit guide. Organizations stocking emergency response supplies can browse emergency and trauma response supplies.
Availability
FDA approved the first over-the-counter naloxone nasal spray, a 4 mg Narcan product, on March 29, 2023. NIDA notes that in some states you can get naloxone from a pharmacist even without a prescription.
What can go wrong
- Overdose can return. Naloxone acts for 30 to 90 minutes while opioids can last longer (NIDA).
- Stronger opioids such as fentanyl can complicate an overdose; CDC notes more than one dose of naloxone may be required in those cases.
- Naloxone only acts on opioids. It has no effect if no opioids are present (NIDA), and it does not treat overdose from other drugs, although CDC says it will not harm the person.
When to get professional help
Immediately. CDC and NIDA both say to call 911 in a suspected overdose, even when naloxone has been used. Naloxone is not a replacement for emergency care. For organizational medication-safety programs, see opioid stewardship programs.
FAQ
What is naloxone?
A medication that can reverse an overdose from opioids (CDC), available as an injectable and a prepackaged nasal spray (NIDA).
How does naloxone work?
It attaches to opioid receptors and reverses and blocks the effects of other opioids (NIDA).
What is naloxone used for?
Reversing an opioid overdose (CDC).
Does naloxone work on every overdose?
No. It reverses opioid overdoses. It has no effect on someone without opioids in their system (NIDA) and will not harm someone overdosing on drugs other than opioids (CDC).
Why call 911 if naloxone was used?
Because naloxone lasts 30 to 90 minutes and opioids can last longer, so the overdose can return (NIDA).
Is naloxone available without a prescription?
FDA approved the first over-the-counter naloxone nasal spray on March 29, 2023. NIDA notes that in some states a pharmacist can provide it without a prescription.
Sources
Date checked: 2026-11-04.
- CDC, Lifesaving Naloxone, page dated June 11, 2025. https://www.cdc.gov/stop-overdose/caring/naloxone.html
- NIDA, DrugFacts: Naloxone, January 2022. https://nida.nih.gov/publications/drugfacts/naloxone
- FDA, FDA approves first over-the-counter naloxone nasal spray, March 29, 2023. https://www.fda.gov/news-events/press-announcements/fda-approves-first-over-counter-naloxone-nasal-spray
