Phencyclidine is an illegal, hallucinogenic drug that was initially used as an anesthetic agent in the 1950s and early 1960s, but was then withdrawn in 1965 because of dissociative hallucinogenic effects that were often disturbing and sometimes severe and prolonged. Phencyclidine is a noncompetitive NMDA (N-methyl-D-aspartate) receptor antagonist and glutamate receptor antagonist, but also interacts with other receptor sites, and may have effects with dopamine, opioid and nicotinic receptors. Phencyclidine disrupts the functioning of receptors for the neurotransmitter glutamate, which plays a major role in the perception of pain as well as in learning, memory, and emotion. It also influences the actions of the neurotransmitter dopamine, which causes the euphoria associated with drug use. Phencyclidine overdose deaths may occur after taking a large dose, though many phencyclidine related deaths result from delusions and other psychological consequences of the drug’s use. There have been reports of death due to accidental drowning, leaping from high places, and motor vehicle accidents in addition to violent episodes of self-mutilation, suicides, and homicides.

Trodusquemine (MSI-1436) is a "first-in-class" highly selective non-competitive, allosteric inhibitor of PTP1B that can cross the blood-brain barrier to suppress feeding and promote insulin sensitivity and glycemic control. Trodusquemine is a naturally occurring cholestane that can be purified from the liver of the dogfish shark, Squalus acanthias, but it can also be manufactured synthetically by a fairly laborious process that requires several weeks. Trodusquemine has potential hypoglycemic, anti-diabetic, anti-obesity, and antineoplastic activities. Upon administration, trodusquemine selectively targets and inhibits PTP1B, thereby preventing PTP1B-mediated signaling. This prevents the dephosphorylation of the insulin receptor, which improves insulin signaling and insulin sensitivity, and decreases blood glucose levels. In susceptible cancer cells, inhibition of PTP1B causes a reduction of tumor cell proliferation.

MK-0686 is a bradykinin B1 receptor antagonist patented by American multinational pharmaceutical company Merck & Co for the treatment of neuropathic pain and inflammation. MK-0686 demonstrates significantly reduced susceptibility to human P-gp mediated efflux and shows good potential for human CNS penetration based on brain levels in CF-1 mice and monkeys. Additionally, MK-0686 also exhibited good CNS bradykinin B1 receptor occupancy in the transgenic rat expressing the human B1 receptor and showed oral efficacy in reducing CFA-induced hyperalgesia in a humanized mouse. Unfortunately, in phase II clinical trials MK-0686 failed to demonstrate efficacy in phase II clinical trials.

Telinavir (previously known as SC-52151) was developed as an anti-HIV aspartyl protease inhibitor for the treatment of HIV Infections. Telinavir participated in Phase I/II clinical study. In spite of the drug was well tolerated no antiviral activity was produced and further development of the drug was discontinued.

Levomequitazine is the L-enantiomer of mequitazine. The antihistaminergic activity mainly resides in the S-enantiomer, L-mequitazine, whereas the anticholinergic activity mainly resides in the D-enantiomer. It was shown, that L-enantiomer of mequitazine is less potent antagonist of human M3 muscarinic acetylcholine receptors than D-enantiomer. In vitro binding studies have shown that the affinity of L-mequitazine for H1 receptors is approximately ten times higher and to muscarinic receptors ten times lower, compared to d-mequitazine. Memory impairment was observed after administration of L-mequitazine 10 mg alone on delayed recall. This could be due to indirect effects of H1 receptor blockade. L-mequitazine 10 mg produced mild driving impairment, whereas L-mequitazine 2.5 and 5.0 mg show no effects on driving. Levomequitazine had been in phase III clinical trials by Pierre Fabre for the treatment of perennial allergic rhinitis and seasonal allergic rhinitis.

Bedoradrine (also known as KUR-1246 or MN-221), an ultra selective beta 2-adrenoceptor agonist, that participated in phase II clinical trials as an adjunct to standard therapy in the management of patients with acute exacerbation of asthma who did not respond to standard therapy. In addition, the drug was involved in trials for the treatment of preterm labor in obstetrical practice. Bedoradrine is also was studied in phase I of clinical trials for its use for treating chronic obstructive pulmonary disease, however, the efficacy for this disease was uncertain.

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.

Vatalanib a potent oral tyrosine kinase inhibitor with a selective range of molecular targets, has been extensively investigated and has shown promising results in patients with solid tumors in early trials. Vatalanib selectively inhibits the tyrosine kinase domains of vascular endothelial growth factor (VEGF) receptor tyrosine kinases (important enzymes in the formation of new blood vessels that contribute to tumor growth and metastasis), platelet-derived growth factor (PDGF) receptor, and c-KIT. The adverse effects of vatalanib appear similar to those of other VEGF inhibitors. In the CONFIRM trials, the most common side effects were high blood pressure, gastrointestinal upset (diarrhea, nausea, and vomiting), fatigue, and dizziness.