Naloxone is an opioid antagonis drug developed by Sankyo in the 1960s. Naloxone is a drug used to counter the effects of opiate overdose, for example heroin or morphine overdose. Naloxone is specifically used to counteract life-threatening depression of the central nervous system and respiratory system. Naloxone is also experimentally used in the treatment for congenital insensitivity to pain with anhidrosis (CIPA), an extremely rare disorder (1 in 125 million) that renders one unable to feel pain. It is marketed under various trademarks including Narcan, Nalone, and Narcanti, and has sometimes been mistakenly called "naltrexate." It is not to be confused with naltrexone, an opioid receptor antagonist with qualitatively different effects, used for dependence treatment rather than emergency overdose treatment.
Naloxone has an extremely high affinity for µ-opioid receptors in the central nervous system. Naloxone is a µ-opioid receptor competitive antagonist, and its rapid blockade of those receptors often produces rapid onset of withdrawal symptoms. Naloxone also has an antagonist action, though with a lower affinity, at k- and d-opioid receptors.
Naloxone is synthesized from thebaine. The chemical structure of naloxone resembles that of oxymorphone, the only difference being the substitution of the N-methyl group with an allyl (prop-2-enyl) group. The name naloxone has been derived from N-allyl and oxymorphone.
Naloxone is most commonly injected intravenously for fastest action. The drug generally acts within a minute, and its effects may last up to 45 minutes. It can also be administered via intramuscular or subcutaneous injection. Use of a wedge device (nasal atomizer) attached to a syringe to create a mist delivering the drug to the nasal mucosa may also be utilized, although this solution is more likely utilized outside of a clinical facility. Naloxone is used orally along with Oxycontin Controlled Release and it helps in reducing the constipation associated with opioids. Enteral administration of Naloxone blocks opioid action at the intestinal receptor level, but has low systemic bioavailability due to marked hepatic first pass metabolism. 
Counteracting opiate overdose and addiction
Naloxone has been distributed as part of emergency kits to heroin users, and this has been shown to reduce rates of fatal overdose. Projects of this type are under way in San Francisco, New Mexico, Philadelphia, New York State, Baltimore, Boston, Los Angeles, Milwaukee, and Chicago, with pilot projects started in Scotland in 2006. Also in the UK, in December 2008 the Welsh Assembly Government announced intention to establish demonstration sites for 'take home' Naloxone. While naloxone is still often used in emergency treatments for opioid overdose, its clinical use in the long-term treatment of opioid addiction is being increasingly superseded by naltrexone. Naltrexone is structurally similar but has a slightly increased affinity for k-opioid receptors over naloxone, can be administered orally, and has a longer duration of action.
Enteral naloxone has been successfully used in the reduction of gastritis and esophagitis associated with opioid therapy in mechanically-ventilated acute care patients.
The combination oxycodone/naloxone is used for the prophylaxis of opioid-induced constipation in patients requiring strong opioid therapy under the trade name Targin and in the Netherlands under Targinact.
Preventing opioid abuse
Naloxone is used as a secondary chemical in the drug Suboxone. Suboxone and Subutex were created to help opiate-addicted patients detox. Suboxone contains four parts buprenorphine and one part naloxone, while Subutex contains only buprenorphrine. Naloxone was added to Suboxone in an effort to dissuade patients from injecting the tablets, due to naloxones ability to block opioid receptors and send the user into immediate withdrawal. Users with a high tolerance however may still be able to abuse Suboxone via injection given that buprenorphine has a higher affinity for opioid receptors than naloxone. Oral or sublingual administration affects only the gastrointestinal tract, and has the added benefit of helping to reverse constipation and lowered bowel motility caused by chronic medical use, or abuse, of a variety of opioids. Because of possible side effects of naloxone in some patients, chemical detox can begin with Suboxone's sister drug, Subutex, which does not contain naloxone. It is common for Suboxone film to be used in all cases unless pregnancy is a concern.
Possible side effects include: change in mood, increased sweating, nausea, nervousness, restlessness, trembling, vomiting, allergic reactions such as rash or swelling, dizziness, fainting, fast or irregular pulse, flushing, headache, heart rhythm changes, seizures, sudden chest pain. Naloxone has been shown to block the action of pain-lowering endorphins which the body produces naturally. The likely reason for this is that these endorphins operate on the same opioid receptors that Naloxone blocks. Naloxone is capable of blocking a placebo pain-lowering response, both in clinical and experimental pain, if the placebo is administered together with a hidden or blind injection of naloxone. Other studies have found that placebo alone can activate the body's µ-opioid endorphin system, delivering pain relief via the same receptor mechanism as morphine.