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.

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.

Benzethidine an opioid analgesic that was forbidden for use.

Betaprodine is an opioid analgesic under international control according to the UN Single Convention 1961. It has been used in obstetrics, as pre-operative medication, for minor surgical procedures.

Diampromide is a synthetic narcotic analgesic. It was designed as a methadone analog and hence with a chiral center similar to that of the parent. Diampromide approximates to the potency of pethidine and morphine in mice and rats, respectively. It has been evaluated in postoperative pain. Diampromide is not found in any pharmaceutical preparations sold in the United States. It is under international control according to the UN Single Convention 1961 and its amendments, Schedule I.

Proheptazine is a substituted azacycloalkane patented by American Home Products Corp. as an opioid analgesic. Proheptazine produces similar effects to other opioids, including analgesia, sedation, euphoria, dizziness and nausea.

Betamethadol or β-methadol is an opioid analgesic under international control according to the UN Single Convention 1961. Betamethadol is an isomer of the racemic mixture of dimepheptanol.

Alphamethadol is a synthetic opioid analgesic. Alphamethadol is composed of two isomers itself, L-α-methadol, and D-α-methadol. L-α-methadol is an important active metabolite of levacetylmethadol (LAAM), a medication therapy for individuals addicted to opiates that provides an alternative to methadone. Isomers of Alphamethadol bind to and activate the μ-opioid receptor; they are active as opioid analgesics.