Naloxone, sold under the brandname Narcan among others, is a medication used to reverse 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.

(+)-Naloxone (dextro-naloxone) is a drug which is the "unnatural" enantiomer of the opioid antagonist drug (-)-naloxone. Unlike "normal" naloxone, (+)-naloxone has no significant affinity for opioid receptors, but instead has been discovered to act as a selective antagonist of Toll-like receptor 4. This receptor is involved in immune system responses, and activation of TLR4 induces glial activation and release of inflammatory mediators such as TNF-a and Interleukin-1.