Nalmefene is the first medication approved for alcoholism with the primary goal of reducing alcohol intake in an as needed approach. Nalmefene received a marketing authorization valid throughout the European Union on February 25, 2013 and is under development in Asia. Nalmefene is an opioid system modulator with a distinct μ, δ, and κ receptor profile. In vitro studies have demonstrated that Nalmefene is a selective opioid receptor ligand with antagonist activity at the μ and δ receptors and partial agonist activity at the κ receptor. In vivo studies have demonstrated that nalmefene reduces alcohol consumption, possibly by modulating cortico-mesolimbic functions. In the US, immediate-release injectable nalmefene was approved in 1995 as an antidote for opioid overdose. It was sold under the trade name Revex. The product was discontinued by its manufacturer around 2008. Currently Nalmefene is sold under the trade name Selincro. Selincro is indicated for the reduction of alcohol consumption in adult patients with alcohol dependence who have a high drinking-risk level, without physical withdrawal symptoms and who do not require immediate detoxification.

Naltrexone is marketed as its hydrochloride salt, naltrexone hydrochloride, under the trade names Revia and Depade. A once-monthly extended-release injectable formulation is marketed under the trade name Vivitrol. VIVITROL is indicated for the treatment of alcohol dependence in patients who are able to abstain from alcohol in an outpatient setting prior to initiation of treatment with VIVITROL. VIVITROL is indicated for the prevention of relapse to opioid dependence, following opioid detoxification. Naltrexone is a pure opiate antagonist and has little or no agonist activity. The mechanism of action of naltrexone in alcoholism is not understood; however, involvement of the endogenous opioid system is suggested by preclinical data. Naltrexone is thought to act as a competitive antagonist at mc, κ, and δ receptors in the CNS, with the highest affinity for the μ receptor. Naltrexone competitively binds to such receptors and may block the effects of endogenous opioids. This leads to the antagonization of most of the subjective and objective effects of opiates, including respiratory depression, miosis, euphoria, and drug craving. The major metabolite of naltrexone, 6-β-naltrexol, is also an opiate antagonist and may contribute to the antagonistic activity of the drug. Low dose naltrexone is an “off label” use of naltrexone. Normal naltrexone usage to break addictions is 50mg – 100mg. Usage of low dose naltrexone ranges in the area of 3 mg – 4.5 mg dosing and is prescribed in an oral pill form and is quite inexpensive. For people with multiple sclerosis, the dosage of LDN ranges from 1.5 to 4.5 ml per day.

Naloxone, sold under the brand name Narcan among others, is a medication used to block the effects of opioids, especially in overdose. Naloxone has an extremely high affinity for μ-opioid receptors in the central nervous system (CNS). Naloxone is a μ-opioid receptor (MOR) inverse agonist, 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 κ- (KOR) and δ-opioid receptors (DOR). If administered in the absence of concomitant opioid use, no functional pharmacological activity occurs (except the inability for the body to combat pain naturally). In contrast to direct opiate agonists, which elicit opiate withdrawal symptoms when discontinued in opiate-tolerant people, no evidence indicates the development of tolerance or dependence on naloxone. The mechanism of action is not completely understood, but studies suggest it functions to produce withdrawal symptoms by competing for opiate receptor sites within the CNS (a competitive antagonist, not a direct agonist), thereby preventing the action of both endogenous and xenobiotic opiates on these receptors without directly producing any effects itself. When administered parenterally (e.g. intravenously or by injection), as is most common, naloxone has a rapid distribution throughout the body. The mean serum half-life has been shown to range from 30 to 81 minutes, shorter than the average half-life of some opiates, necessitating repeat dosing if opioid receptors must be stopped from triggering for an extended period. Naloxone is primarily metabolized by the liver. Its major metabolite is naloxone-3-glucuronide, which is excreted in the urine. Naloxone is useful both in acute opioid overdose and in reducing respiratory or mental depression due to opioids. Whether it is useful in those in cardiac arrest due to an opioid overdose is unclear. Naloxone is poorly absorbed when taken by mouth, so it is commonly combined with a number of oral opioid preparations, including buprenorphine and pentazocine, so that when taken orally, just the opioid has an effect, but if misused by injecting, the naloxone blocks the effect of the opioid. In a meta-analysis of people with shock, including septic, cardiogenic, hemorrhagic, or spinal shock, those who received naloxone had improved blood flow. Naloxone is also experimentally used in the treatment for congenital insensitivity to pain with anhidrosis, an extremely rare disorder (one in 125 million) that renders one unable to feel pain or differentiate temperatures. Naloxone can also be used as an antidote in overdose of clonidine, a medication that lowers blood pressure.