Some additional information: keep more than one. You often need more depending on how much of the opioid was used. It's not uncommon to need a few. If there is no response after a few minutes use another.Narcan is available over the counter at most pharmacies in the U.S. It reverses the symptoms of opioid overdose, has a four-year shelf life, and is harmless if administered to a person not under the influence of opioids. It's a good idea to keep one at home if you live in the U.S., much like having a fire extinguisher. You may never use it, but it’s safer to have one just in case.