Naloxone hydrochloride is an agent capable of antagonizing respiratory depression and analgesic actions which are inherent to the opioid by competitively acting at opioid receptors. It greatly contributed to basic research on antagonistic action of opioid receptors due to its high affinity to opioid receptors, in particular, micro-receptor. Naloxone has been recommended as an analeptic agent at a guideline level for patients with revealed or suspicious opioid addiction. Further, it has also been used as a preventive and treatment agent for spinal cord ischemia. Moreover, even though it has been confirmed in 1980's that naloxone has vasopressor effect in septic shock, further clinical trials are required for its wide clinical application.