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.

Axelopran (previously known as TD-1211), a peripherally selective, multivalent µ-opioid receptor antagonist that is under development by Theravance Biopharma. This drug participated in phase II clinical trials in subjects with opioid-induced constipation. The most common adverse events were abdominal pain, nausea, and diarrhea. There were no indications of opioid withdrawal effects or reductions in opioid analgesia in patients treated with axelopran.

Nalmexone is an opioid partial agonist or mixed agonist-antagonist with both analgesic and narcotic antagonist properties. In preclinical models parenteral nalmexone was a moderately active antagonist and therefore might have low abuse potential. At the same time, early work in man indicated analgesic activity in doses above 20 mg.

Zenazocine is an opioid analgesic that mixes both agonist/antagonist activities. This compound participated in phase II clinical trial, however, the further development was ultimately halted and it has never been marketed.

Levallorphan (brand name Lorfan), is an opiate antagonist of morphine family. Levallorphan was formerly used in general anesthesia, mainly to reverse the respiratory depression produced by opioid analgesics and barbiturates used for induction of surgical anaesthesia whilst maintaining a degree of analgesia. Levallorphan was also used in combination with opioid analgesics to reduce their side effects, mainly in obstetrics. The combination of levallorphan with pethidine was used so frequently, a standardized formulation was made available, known as Pethilorfan, by Roche Products Ltd in later 1950s. Is known to be used for narcotic overdose. Levallorphan is similar to naloxone but differs from naloxone in that it also possesses some agonist properties. It acts as an antagonist and partial agonist of the mu opioid receptor (MOR). Levallorphan can produce severe mental reactions at sufficient doses including hallucinations, dissociation, and other psychotomimetic effects, dysphoria, anxiety, confusion, dizziness, disorientation, derealization, feelings of drunkenness, and bizarre, unusual, or disturbing dreams.