Naloxone blocks or reverses the effects of opioid medication, including extreme drowsiness, slowed breathing, or loss of consciousness. An opioid is sometimes called a narcotic. Naloxone is used to treat a narcotic overdose in an emergency situation. This medicine should not be used in place of emergency medical care for an overdose. Naloxone is also used to help diagnose whether a person has used an overdose of an opioid.