Narcan contains one active ingredient: naloxone hydrochloride, a compound that rapidly reverses opioid overdoses by knocking opioid molecules off their receptors in the brain. The over-the-counter nasal spray delivers 4 milligrams of naloxone in a single burst, along with a short list of inactive ingredients that keep the solution stable and effective inside the device.
The Active Ingredient: Naloxone
Naloxone hydrochloride is classified as an opioid antagonist, meaning it blocks the effects of opioids rather than producing any of its own. It works through competitive displacement: naloxone has such a strong attraction to the same receptors that opioids bind to (particularly the mu-opioid receptor) that it physically pushes opioid molecules out of the way and takes their place. Once naloxone occupies those receptors, the opioid can no longer suppress breathing or consciousness, and the person’s body begins recovering within minutes.
What makes naloxone especially useful in emergencies is that it functions almost like a lock-and-key replacement. It fits into the receptor but doesn’t activate it, so it produces no high, no pain relief, and no respiratory depression. It simply sits there, blocking opioids from doing their job. At standard doses, naloxone primarily targets mu-opioid receptors while having minimal effects on other opioid receptor types in the nervous system.
If naloxone is given to someone who doesn’t have opioids in their system, it does essentially nothing. The National Institute on Drug Abuse describes it plainly: naloxone has no effect on a person without opioids in their body. This makes it remarkably safe for bystanders to use, even when they’re unsure whether an overdose involves opioids.
Inactive Ingredients in the Nasal Spray
Beyond naloxone itself, the spray contains five inactive ingredients, each serving a specific purpose:
- Benzalkonium chloride acts as a preservative, preventing bacterial growth in the liquid solution.
- Disodium EDTA (a stabilizer) keeps the naloxone from breaking down by binding to trace metals that could degrade the formula.
- Sodium chloride adjusts the salt concentration so the spray is comfortable against nasal tissue.
- Hydrochloric acid fine-tunes the pH, which the FDA label lists as falling between 3.5 and 5.5.
- Purified water serves as the base that carries everything else.
None of these ingredients are unique to Narcan. They’re common across nasal sprays and injectable medications. The formulation is designed to keep the naloxone stable at room temperature while ensuring it absorbs quickly through the lining of the nose.
The Delivery Device
Each Narcan nasal spray unit is a single-use device. You can’t partially use it or save half for later. One press of the plunger delivers the full 4 mg dose into one nostril. The device requires no assembly, no priming, and no medical training. It’s packaged in a sealed blister that protects it from light and moisture until you’re ready to use it.
If symptoms return or the person doesn’t respond within two to three minutes, a second device can be used in the other nostril. Narcan kits typically come with two spray units for this reason.
How Quickly It Works and How Long It Lasts
Naloxone delivered through the nose takes effect within a few minutes as it absorbs through the nasal membranes into the bloodstream. The challenge with naloxone is that its effects wear off faster than most opioids last. This is why someone who initially recovers can slip back into overdose once the naloxone clears their system. Emergency medical care remains important even after a successful dose.
The typical shelf life of Narcan is about two years from the date of manufacture. It should be stored between roughly 59°F and 86°F (15°C to 30°C), which covers most indoor environments. Extreme heat, like a car dashboard in summer, or freezing temperatures can degrade the naloxone over time, though expired Narcan is generally considered better than no Narcan at all in an emergency.
Over-the-Counter Availability
On March 29, 2023, the FDA approved Narcan 4 mg nasal spray for over-the-counter sale, making it the first naloxone product available without a prescription in the United States. You can now find it at pharmacies, some grocery stores, and through community distribution programs. The move to nonprescription status removed a significant barrier, since previously many states required either a prescription or a standing order from a pharmacist to obtain it.
The 4 mg nasal spray is the formulation designed for public use. Other naloxone products exist in injectable forms used by paramedics and hospitals, but the nasal spray is specifically built so that anyone, regardless of medical background, can administer it during a suspected overdose.