Ensaculin is related to naturally occurring benzopyranones like scoparone. The compound is a potent functional antagonist of excitatory amino acid-induced convulsions and mortality. In receptor-binding studies, Ensaculin showed high affinity to dopaminergic (D2, D3), serotoninergic (5-HT1A, 5-HT7), and adrenergic (A1a, A1b) receptors in the nanomolar range. Ensaculin antagonizes NMDA responses in a voltage-dependent manner. Various studies support the notion that this compound could indeed have a broad range of nootropic properties. Although few patients presented postural hypotension and dizziness after receiving ensaculin in phase I clinical trials, this drug candidate was further discontinued in phase III due to potential side effects.

Hydroxyflutamide is the major active metabolite of flutamide. Flutamide undergoes extensive first-pass metabolism by CYP1A2 to its metabolite hydroxyflutamide and its hydrolysis product, 3-trifluoromethyl-4-nitroaniline. Hydroxyflutamide is a more powerful antiandrogen in vivo, with higher affinity for the receptor than that of flutamide. Hydroxyflutamide is in phase II clinical trials for the treatment of prostate cancer. However, a drug resistance problem appears after about one year's treatment. Per-residue free energy decomposition analyses indicate that N705, T877, and M895 androgen receptor mutations are vital residues in the agonist/antagonist mechanism of hydroxyflutamide.

AstraZeneca (formerly Astra) is developing robalzotan (NAD-299, AZD-7371), a 5-HT1A antagonist, for the potential treatment of depression and anxiety. The compound has entered phase II trials but was discontinued. Then it investigated for the treatment of irritable bowel syndrome, but the study was prematurely terminated. The same final has expected the development of robalzotan in phase II to treat overactive bladder, this investigation was terminated in July 2005.

Cidoxepin is the cis-isomer of the widely prescribed tricyclic compound doxepin. Commercial preparations of the tricyclic anti-depressant doxepin contain 15% of the more active cis-doxepin and 85% of the trans-isomer. Elorac, Inc., a rapidly growing specialty pharmaceutical company focused on the treatment of dermatological disorders, is pleased to announce that it has acquired worldwide rights to the active agent Cidoxepin from Gideon Pharmaceuticals. Cidoxepin appears to be much more potent than doxepin while having less sedative and cholinergic side effects. Elorac plans to develop oral formulations of the drug to treat urticaria and topical formulations for treatment of atopic and contact dermatitis.

Velneperit, also known as S-2367, is a once-daily, oral, centrally acting, small molecule neuropeptide Y (NPY) Y5 receptor antagonist that was discovered by Shionogi Research Laboratories. It was developed for the oral treatment of obesity. Velneperit was in phase II trials, however, development was discontinued.

Zaurategrast (CDP323) is an ethyl ester prodrug of CT7758, a potent carboxylic acid antagonist of integrin alpha4-beta1 (α4β1) or very late antigen 4 (VLA4). CDP323 was under development with UCB and Biogen Idec for the treatment of multiple sclerosis. Its development was discontinued in 2009 based on inadequate interim efficacy data in a phase II clinical trial.

Traxoprodil (CP-101,606) is a potent, selective N-Methyl-D-aspartate (NMDA) receptor (NR2B subunit) antagonist under development by Pfizer for its potential as a neuroprotectant in head injury and neurodegenerative disease. It is in phase II trials in the US and in phase I in Japan for the potential treatment of head injury, such as, Depressive Disorder, Major and Parkinson's Disease. CP-101,606 does not protect against glutamate-induced neurotoxicity in cultured cerebellar neurons, up to a dose of 10 uM. These results are consistent with CP-101,606 being a potent NMDA antagonist, selective for the type of NMDA receptor associated with the hippocampus. Some further investigation revealed that CP-101,606 was associated with a dose-related dissociation and amnesia. These results support the hypothesis that glutamate antagonists may be useful antidyskinetic agents. However, future studies will have to determine if the benefits of dyskinesia suppression can be achieved without adverse cognitive effects.

Tesmilifene is a small-molecule antineoplastic drug and chemopotentiator that was under development by YM BioSciences for the treatment of breast cancer. Tesmilifene was developed as a selective ligand of the antiestrogen binding sites without estrogen receptor affinity. Tesmilifene potentiates the cytotoxicity of a variety of chemotherapy drugs in vitro and in vivo. Tesmilifene in combination with doxorubicin provides an unexpected and very large survival advantage over doxorubicin alone in a randomized trial in phase III clinical trial in advanced breast cancer. Unfortunately, Tesmilifene application associated with high rate disease and treatment-related adverse events and poor quality of life. Based on these results further development of Tesmilifene was discontinued

Metitepine, a psychotropic agent was developed as a non-selective antagonist of serotonin, dopamine, and adrenergic receptors. Metitepine has never been marketed.

Sunepitron (CP-93,393) is an anxiolytic drug with highly selective serotonin 5-hydroxytryptamine 1A autoreceptor agonist, alpha2-adrenergic antagonist, and dopamine D2 agonist properties. Sunepitron hydrochloride had been in Phase III clinical trials by Pfizer for the treatment of anxiety disorder and depression. However, this research has been discontinued.