Naloxone, sold under the brandname Narcan among others, is a medication used to block the effects of opioids, especially in overdose. Naloxone may be combined within the same pill as an opioid to decrease the risk of misuse. When given intravenously, it works within two minutes, and when injected into a muscle, it works within five minutes. The medication may also be used in the nose. The effects of naloxone last about half an hour to an hour. Multiple doses may be required, as the duration of action of most opioids is greater than that of naloxone.