Naloxone is the emergency antidote for overdoses caused by heroin and other opiates or opioids (such as methadone, morphine and fentanyl).
The main life-threatening effect of heroin and other opiates is to slow down and stop breathing. Naloxone blocks this effect and reverses breathing difficulties.
Naloxone is a prescription-only medicine, so pharmacies cannot sell it over the counter. But drug services can supply it without a prescription. And anyone can use it to save a life in an emergency.