Quadazocine is a substituted hexahydro-2,6-methano-3-benzazocine patented by Sterling Drug Inc. as analgesics and narcotic antagonist. Quadazocine is a potent antagonist of μ opioid receptor, less potent antagonist of κ and δ opioid receptors. In monkeys for whom responding was reinforced by food delivery, quadazocine blocks the rate-decreasing effects of the µ-agonists alfentanil and fentanyl with greater potency than it blocked the rate-decreasing effects of the κ-agonists U69,593

Cyclazocine is a mixed opioid agonist/antagonist, an agonist of kappa opioid receptor, and a partial agonist of mu opioid receptor. The drug has analgesic activity and dose 0.25-0.5 mg/70 kg is equivalent to 10 mg/75 kg of morphine. Cyclazocine is a long-acting mu-opioid antagonist in human and was studied for the treatment of addiction to opioids and cocaine. Induction of the drug leads to dysphoria, hallucination, irritability, and sleeplessness.

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.

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.

Samidorphan, which was developed by Alkermes, is an opioid receptor antagonist that has been co-formulated with olanzapine into a single-dose oral tablet to mitigate the risk of weight gain while providing the therapeutic effect of olanzapine. In June 2021, the Food and Drug Administration (FDA) approved Lybalvi (olanzapine/samidorphan) for indications including treatment of adults with schizophrenia and/or bipolar I disorder (acute manic episodes or acute episodes with mixed features).

MOVANTIK (naloxegol) is a peripherally-acting mu-opioid receptor antagonist indicated for the treatment of opioid-induced constipation (OIC) in adult patients with chronic noncancer pain. It is being investigated for the treatment of constipation as a side effect of prescription opioid pain medicines.

Methylnaltrexone, is a peripherally acting μ-opioid receptor antagonist that acts on the gastrointestinal tract to inhibit the opioid-induced decrease in gastric motility and transit time. It is used to treat opiate-induced constipation in adults with chronic non-cancer pain and in adults with advanced illness who are receiving palliative care.

Alvimopan (LY246736, ADL 8-2698, trade name Entereg) is a potent, peripherally selective mu-opioid receptor antagonist. Alvimopan was developed by Adolor Corporation (now Cubist Pharmaceuticals) and GlaxoSmithKline for the treatment of postoperative ileus. Postoperative ileus is the impairment of gastrointestinal motility after intra-abdominal surgery or other non-abdominal surgeries. This may potentially delay gastrointestinal recovery and hospital discharge until its resolution. Morphine and other mu-opioid receptor agonists are universally used for the treatment of acute postsurgical pain; however, they are known to have an inhibitory effect on gastrointestinal motility and may prolong the duration of postoperative ileus. Following oral administration, alvimopan antagonizes the peripheral effects of opioids on gastrointestinal motility and secretion by competitively binding to gastrointestinal tract mu-opioid receptors.

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.