Naloxone, sold under the brandname Narcan among others, is a medication used to block the effects of opioids, especially in overdose.[1] Naloxone may be combined with an opioid (in the same pill) to decrease the risk of opioid misuse.[1] When given intravenously, naloxone works within two minutes, and when injected into a muscle, it works within five minutes;[1] it may also be sprayed into the nose.[3] The effects of naloxone last about half an hour to an hour.[4] Multiple doses may be required, as the duration of action of most opioids is greater than that of naloxone.[1]
Administration to opioid-dependent individuals may cause symptoms of opioid withdrawal, including restlessness, agitation, nausea, vomiting, a fast heart rate, and sweating.[1] To prevent this, small doses every few minutes can be given until the desired effect is reached.[1] In those with previous heart disease or taking medications that negatively affect the heart, further heart problems have occurred.[1] It appears to be safe in pregnancy, after having been given to a limited number of women.[5] Naloxone is a non-selective and competitive opioid receptor antagonist.[6][7] It works by reversing the depression of the central nervous system and respiratory system caused by opioids.[1]
Source: https://en.wikipedia.org/wiki/Naloxone