Mirfentanil was developed as CNS analgesic with a short duration of action. It induced antinociception predominately through mu opioid receptors. It was shown that at doses larger than those, which exert opioid effects, mirfentanil had nonopioid analgesic effects. The drug was successfully encapsulated in liposomes having a variety of compositions. The lipid composition of the formulation was varied to optimize the stabilization of liposomes and the encapsulation of solutes. Mirfentanil participated in phase II clinical trials for the treatment of pain. However, this study was discontinued.

Trefentanil is a short-acting synthetic opioid of the piperidine class. The drug caused potent analgesia with the peak effect occurring 3 min after injection. There was no significant difference in analgesic potency of trefentanil and alfentanil as measured by tolerance to tibial pressure at 3 min. Trefentanil had a pharmacokinetic and pharmacodynamic profile similar to alfentanil, with a small extent of tissue distribution and a rapid blood/brain equilibration. Trefentanil caused significant respiratory depression at doses of 32 ug/kg and 64 ug/kg. It is a mu-opioid receptor agonist. Trefentanil produced naloxone reversible anti-nociception equi-efficacious to that of fentanyl.

Norbolethone is a 19-nor anabolic steroid first synthesized in 1966. During the 1960s it was administered to humans in efficacy studies concerned with short stature and underweight conditions. It has never been reported by doping control laboratories prior to 2001. Norbolethone matches the description for what is described as a "designer steroid. " In fact, Norbolethone was given in clinical trials over 30 years ago and never given the green light. No supply was ever manufactured, and no test was ever developed to detect this substance, yet ironically, it was suspected of being used in the 2000 Olympics based on blood and urine assays done by the IOC. Norbolethone was used in the treatment of idiopathic underweight, prevention of indomethacin-induced intestinal ulcers.

Meclonazepam (Ro11-3128 or 3-methylclonazepam) is a benzodiazepine derivative. It exerts anxiolytic activity. Meclonazepam demonstrated anti-schistosomal action, it causes spastic paralysis, calcium influx and tegumental disruption in the parasites. Contracturant effect of meclonazepam is not a result of its binding to the worm benzodiazepine binding sites.

Ocfentanil, a compound structurally similar to the opioid analgesic fentanyl, was developed in the early 1990’s with the hope that it would provide a better clinical safety profile than fentanyl. The receptor pharmacology of ocfentanil appears to share pharmacodynamic effects with fentanyl and other μ opioid agonists, including analgesia, sedation, and respiratory depression. In rodents, ocfentanil was approximately 2.5 times more potent as an analgesic than fentanyl and had a shorter duration of action. Because the preclinical research suggested that ocfentanil had a better safety profile than fentanyl, it was selected for clinical evaluation. Like other μ opioid agonists, ocfentanil has been reported to produce itching, nausea, sedation, and severe respiratory depression. Chest pain, psychosis, and agitation have also been reported. In humans, however, ocfentanil had a similar potency (3 ug/kg ocfentanil produced effects that were comparable to 5 ug/kg fentanyl) and side-effects profile as fentanyl so further clinical development was discontinued. Ocfentanil is not approved in any country for medical useand is under national control in Canada, the United Kingdom, and China.

HU-308 ([(1R,2R,5R)-2-[2,6-dimethoxy-4-(2-methyloctan-2-yl)phenyl]-7,7-dimethyl-4-bicyclo[3.1.1]hept-3-enyl]methanol) is a potent, selective agonist for the CB2 receptor. The synthesis and characterization took place in the laboratory of Prof. Mechoulam at the Hebrew University of Jerusalem in the late 1990s. It has analgesic effects, promotes proliferation of neural stem cells,[3] and protects both liver and blood vessel tissues against oxidative stress via inhibition of TNF-α. In vivo, HU-308 has hypotensive, analgesic, and anti-inflammatory activities in mice that can be reversed by the CB2 receptor antagonist SR 144528 but not the CB1 receptor antagonist rimonabant. Pretreatment of mice with HU-308 decreases the I/R-induced tissue damage, inflammatory cell infiltration, tissue, and serum TNF-α, MIP-1, and MIP-2 levels, tissue lipid peroxidation, and apoptosis. HU-308 increases proliferation of HT29 colon cancer cells and growth of tumors in an HT29 mouse xenograft model. The physiological and toxicological properties of this compound have not been evaluated in humans.

Clonitazene is a synthetic opioid analgesic, structurally related to etonitazene. In the USA clonitazene is a schedule I narcotic controlled substance.