Naloxone is approved by the Food and Drug Administration (FDA) to rapidly reverse opioid overdose. It is an opioid antagonist—meaning it binds to opioid receptors to reverse and block the effects of opioids, such as fentanyl, heroin, and oxycodone. Administered when a patient is showing signs of opioid overdose, naloxone is a temporary treatment and its effects do not last long.