Naloxone

Naloxone (often called Narcan), is a medication. It is used to reverse the effects of opioid painkillers, especially when a person has overdosed on opioids. Examples of opioids include: 
These painkillers are central nervous system depressants. This means they slow down certain areas of the brain. If a person takes too many opiates, this can shut down the part of the brain that controls breathing. The person may become unable to breathe and die.
When a person has taken too much of one of these painkillers, naloxone can reverse the painkillers' effects and save the person's life.
Naloxone may be mixed into the same pill as an opioid painkiller to decrease the risk of misuse. 
When given intravenously (into a needle placed into a vein), naloxone works within two minutes. When injected into a muscle, it works within five minutes. The medication may also be shot up the nose. 
The effects of naloxone last about half an hour to an hour. Since most opioids last longer than naloxone, a person may need several doses of naloxone to fight the effects of an overdose.
How does naloxone work?
When a person takes opioids, the opioids have to attach to certain receptor sites in the brain in order to work, like a lock in a keyhole. Once the opioids attach to these opiate receptor sites - like a lock fitting into a keyhole - the opiates start to work. They kill pain, create euphoria, and make people feel calm and relaxed. But if a person takes too many opiates, they can also make it impossible to breathe.
Naloxone fits better onto these opiate receptor sites than actual opiates do. If a person takes naloxone, the naloxone will throw any opiate off of the opiate receptor sites (like a key getting taken out of a door). Naloxone will stay attached to these opiate receptor sites. This reverses the effects of the opiates that the person took.
Side effects.
Naloxone reverses the effects of opiates. Because of this, if a person who is addicted to opiates gets naloxone, they will have symptoms of opioid "withdrawal". People have withdrawal symptoms when their body gets used to having opiates all the time.
Because naloxone reverses the effects of opiates, the side effects of naloxone can include restlessness, agitation, nausea, vomiting, a fast heart rate, pain, and sweating. To prevent this, small doses every few minutes can be given until the desired effect is reached. 
Naloxone has to be given carefully to people with heart disease. Naloxone can cause more heart problems, like changes in the rhythm of the heart beat, in these people. 
Naloxone seems to be safe in pregnant women. Naloxone is a pure opioid antagonist. 
In rare cases, naloxone causes seizures and pulmonary edema (fluid in the lungs).
History.
Naloxone was patented in 1961 by Jack Fishman, Mozes J. Lewenstein, and the company Daiichi Sankyo. The drug was approved for opioid overdose by the Food and Drug Administration (FDA) in 1971. It is on the World Health Organization's Model List of Essential Medicines, the most important medications needed in a basic health system. 
Naloxone is available as a generic medication and is not very expensive. Its wholesale price is between $0.50 and $5.30 USD per dose.
Medical uses.
Opiate overdose.
Naloxone can be used to reverse opioid overdose and to reduce the slowed breathing or mental depression that opioids can cause.
Naloxone is included as a part of emergency overdose response kits distributed to heroin and other opioid drug users. This has been shown to reduce deaths due to overdose. 
A prescription for naloxone is recommended if a person is:
If naloxone is prescribed to a person, that person should also be taught about how to prevent, identify, and react to an overdose, including how to perform rescue breathing, CPR, and how to call an emergency telephone number like 9-1-1.
Preventing opioid abuse.
Naloxone may be mixed with a number of opioids like buprenorphine. (Buprenorphine mixed with naloxone is called Suboxone.) Buprenorphine is used to decrease cravings for opiates. When buprenorphine and naloxone are mixed, and taken by mouth, only buprenorphine has an effect. But if a person misuses Suboxone by injecting it or taking large doses, the naloxone blocks the effect of the opioid. This combination is used to try to prevent abuse.