Phenomorphan is the μ-opioid receptor agonist. Phenomorphan is a synthetic narcotic analgesic structurally related to racemorphan and racemethorphan. It has no accepted medicinal value in the United States.

Properidine is an isopropyl analog of pethidine that acts as opioid analgesic.

Phenampromide is an opioid analgesic, which is considered to be structurally similar to isomethadone. Phenampromide belongs to the ampromide family of drugs, which also include propiram and diampromide. According to the literature, (R)-phenampromide has greater analgesic potency than its (S)-enantiomer. Synthetic narcotic analgesic phenampromide is under international control according to the UN Single Convention 1961 and its amendments, Schedule I.

Nicocodine is an opioid related to codeine. It is also an antitussive agent. Nicocodine exhibits at least twice the potency of codeine in clinical experiments. The study of the pharmacokinetic behaviour of nicocodine by means of blood and brain level curves of rats after i .v. application showed that the penetration of the blood brain barrier seems to be favoured for nicocodine. The detected peak concentration of nicocodine in brain after i.v. application is 4.4 times higher than the blood level values at the same time - codeine the main metabolite is detected in almost equal amounts in brain and blood. A comparative assay of codeine and nicocodine after p.o. application of equimolar doses per kg body weight revealed that predominantly codeine is found in brain and its peak value after nicocodine administration is 3-fold higher than after codeine administration. Nicocodine is hydrolysable to morphine and the WHO Expert Committee on Addiction-Producing Drugs (1962) recommended its international control as a narcotic, like other convertible drugs in the morphine series.

Mecloqualone is a quinazoline-class GABAergic and an analog of methaqualone. It acts as an agonist of the beta subtype of GABAa receptor and induces sedative, hypnotic and anxiolytic effects. Mecloqualone was marketed (mostly in france) under the names Nubrene and Casfen for the treatment of insomnia. Mecloqualone is no longer prescribed because of concerns about its potential for abuse and overdose. In the United States, it is registered as a Schedule-I non-narcotic controlled substance.

Myrophine is an opiate analog and long-acting prodrug for morphine with a slow onset of effects. It is weaker than morphine as an analgesic but longer-lasting in effects and was thought to have a more local anesthetic effect than morphine, though with a somewhat greater tendency to cause histamine reactions like itching and rash. In addiction studies conducted in human subjects in the 1950s, myrophine did not substitute for morphine in withdrawal, did not produce notable morphine-like effects, and did not produce addiction or dependence regardless of dose or how it was administered.

Eticyclidine (N-ethyl-1-phenylcyclohexylamine) is a phencyclidine derivative exerting nearly the same pharmacological profile as the parent compound. In rodents, it induces stereotypy, ataxia, interoceptive effect and hypothermia.

Desomorphine is the common name for 4,5--epoxy-17- methylmorphinan-3-ol or dihydrodesoxymorphine-D. It is an opioid analogue and morphine derivative in which the 6-hydroxyl group and the double bond at carbons 7 and 8 of morphine are reduced. Desomorphine can cross the blood–brain barrier, binding to opioid receptors, similar to the pharmacokinetic distribution of all phenanthrene-structured alkaloids. Taking Desomorphine causes euphoria as well as sedative and analgesic relief. In addition to its faster onset than other powerful painkillers drugs such as morphine, desomorphine also initiates less sedative effects and seems to have favorable postoperative results, such as reduced need for catheterization, less dizziness, and decreased vomiting incidence. In comparison with Morphine, Desomorphine is faster reduced. It follows that it has to be taken it more frequently to get the same effects. Furthermore, it causes side effects such as respiratory and gastrointestinal problems and increased blood pressure. In addition, Desomorphine’s withdrawal symptoms are up to three times longer than Morphine’s. This leads to the conclusion that Desomorphine is more addictive. At present, desomorphine is classified as a narcotic drug (DEA code number 9055) in Schedule I of the U.S. Controlled Substances Act and is listed as a controlled substance under the international Single Convention on Narcotic Drugs of 1961.

Etonitazene is a potent and selective mu-opioid agonist. It was developed in CIBA. Administration of etonitazene may induce respiratory depression, and therefor etonitazene is not used in humans. Etonitazene is explicitly listed as an illegal drug under UN convention and is illegal throughout the world.

Carfentanil is a synthetic fentanyl analog. It is a mu-opioid receptor agonist with an estimated analgesic potency approximately 10,000 times that of morphine and 20-30 times that of fentanyl, based on animal studies. Receptor binding studies have shown that carfentanil binds selectively and competitively to the μ subtype of opioid receptors relative to δ and κ opioid receptors. Preclinical studies have demonstrated that the pharmacodynamic effects, such as analgesia and constipation, produced by carfentanil are similar to other μ opioid agonists. Its extreme potency and propensity to produce rapid and profound respiratory depression has prompted recommendations that an opioid antagonist, such as naloxone or naltrexone, be available whenever carfentanil is used or suspected to be present. Carfentanil (Wildnil) has been used in veterinary as a prescription-only general anesthetic for intramuscular injection in large animals. Carfentanil is no longer FDA-approved for use in animals after Wildlife Laboratories withdrew the application for Wildnil. Carfentanyl is increasingly involved in opioid overdose deaths among illicit opioid users.