Known brand names include Narcan, Rextovy, and Zimhi.
An opioid antagonist that rapidly reverses opioid overdose, especially slowed or stopped breathing. It is given by injection in the hospital or as a nasal spray by family members and bystanders while waiting for emergency help.
Naloxone competes with opioids for the same receptors in the brain, binding most strongly to the mu receptor, and pushes them off. Once there, it blocks the receptor without switching it on, so on its own it does almost nothing. This quickly reverses the sleepiness, slowed breathing, and low blood pressure the opioid caused. The label notes that the exact way it works is not fully understood.
Given into a vein, it usually starts working within two minutes, and a little more slowly in a muscle or under the skin. Its effect often wears off before the opioid's does, so breathing can slow again and repeat doses may be needed. In someone whose body depends on opioids, it can set off withdrawal within minutes, which usually eases in about two hours. It does not cause tolerance or dependence, but it may only partly reverse opioids such as buprenorphine.
Naloxone reverses an opioid overdose, in which an opioid leaves a person too sleepy to wake and slows or stops their breathing. It can fully or partly undo the effects of both natural and man-made opioids. As a nasal spray, someone nearby, such as a family member, can give it right away in an emergency, and emergency help is still called.
The nasal spray is approved for people of all ages. The injection, given into a vein, a muscle, or under the skin, reverses opioids used during surgery, eases the effects in newborns of opioids the mother received before delivery, and helps confirm whether an overdose is caused by opioids. It may also be added to raise blood pressure in septic shock, though this has not been shown to help people survive. It does not reverse slowed breathing caused by drugs that are not opioids.
In someone who depends on opioids, it can trigger sudden withdrawal: body aches, sweating, a runny nose, yawning, diarrhea, nausea, fever, a racing heart, and irritability. In newborns, that withdrawal can be life-threatening. The label also warns that breathing can slow again when it wears off, that seizures can happen, and that sudden reversal after surgery can cause serious heart and lung problems. The nasal spray can cause a dry or stuffy nose, headache, and higher blood pressure.