Naloxone is an opioid antagonist medication used to block or reverse the effects of opioid drugs, particularly within the setting of drug overdoses which are rapidly becoming a leading cause of death worldwide. More specifically, naloxone has a high affinity for μ-opioid receptors, where it acts as an inverse agonist, causing the rapid removal of any other drugs bound to these receptors. When taken in large quantities, opioid medications such as morphine, hydromorphone, methadone, heroin, or fentanyl are capable of causing life-threatening symptoms such as respiratory depression, reduced heart rate, slurred speech, drowsiness, and constricted pupils. If untreated, this can progress to vomiting, absent pulse and breathing, loss of consciousness, and even death. Naloxone is indicated for the rapid reversal of these symptoms of central nervous system depression in opioid overdose. It's important to note that naloxone only works on opioid receptors within the body, and is therefore not capable of reversing the effects of non-opioid medications such as stimulants like methamphetamine or cocaine, or benzodiazepines like lorazepam or diazepam. Also known as the brand name product Narcan, naloxone is currently available by intramuscular (IM) or subcutaneous (SubQ) injection, nasal spray, or intravenous (IV) infusion. Naloxone IM injections are commonly available in the form of "kits", which is ideal for making overdose treatment accessible and readily available for administration by minimally trained individuals within the community. Kits commonly include the supplies necessary to treat an overdose in a non-medical setting such as alcohol swabs, syringes, a rescue breathing mask, and instructions for use. Frequently also carried by medical and emergency personnel and at events known to be associated with heavy drug use like music festivals, naloxone kits are considered a key component of harm reduction strategies. There are over-the-counter nasal sprays available. When injected intramuscularly (IM), naloxone acts within three to five minutes. Administration of naloxone is associated with very few side effects. Notably, if injected into a person not currently using opioid medications, there would be no noticeable effects at all. However, for individuals using opioid medications or experiencing an overdose, IM injection of naloxone rapidly reverses opioid effects and can cause the injected individual to immediately experience withdrawal symptoms. Common symptoms of opioid withdrawal include nausea, vomiting, sweating, runny nose, aches, and diarrhea. Although certainly physically uncomfortable, opioid withdrawal symptoms are not life-threatening; administration of naloxone is, therefore, appropriate for any person appearing to have any symptoms of an opioid overdose. Due to its short duration of action, persons injected with naloxone should be monitored for responsiveness and potentially injected a second time or taken to the hospital. Naloxone is also available within the combination product Suboxone with the opioid medication buprenorphine. Suboxone is used for the maintenance treatment of opioid dependence and addiction. When taken orally, naloxone has no pharmacological effect and does not reduce the effectiveness of the opioid effect of buprenorphine. The primary purpose of including naloxone within Suboxone is to act as a deterrent to injection, as injected naloxone would rapidly reverse the effects of buprenorphine. Naloxone was granted FDA approval on 13 April 1971.