Volinanserin (MDL-100,907) is a highly selective 5-HT2A receptor antagonist. It is widely used in scientific research to investigate the function of the 5-HT2A receptor. Volinanserin is also being trialed as a potential antipsychotic, antidepressant and treatment for insomnia. Volinanserin (M-100907) was in phase III trials for chronic schizophrenia. In August 1999, development was discontinued for acute schizophrenia (schizoaffective disorder) on the basis of poor results. M-100907 is also active in animal models involving blockade of NMDA glutamatergic channel receptors, an effect known to resemble some behavioral symptoms of schizophrenia in man. M-100907 is also claimed in other patents for the treatment of thromboembolic disorders, for the treatment of various developmental neurological disorders such as autism and attention deficit hyperactivity disorder.

Idazoxan is an alpha2 receptor antagonist which also shows activity at imidazoline I1 and I2 receptors and modulates the release of dopamine. Idazoxan was in phase II development in the US. Later the development of idazoxan for schizophrenia was discontinued. It was also in clinical trials for cognition disorders in United Kingdom, and was also discontinued. Idazoxan is used in scientific research as a tool for the study of alpha 2-adrenoceptors.

Bifeprunox, code name DU-127,090 is an atypical antipsychotic agent, which combines minimal D2 receptor agonism with 5-HT receptor agonism. Bifeprunox was in phase III of clinical trials for the treatment of schizophrenia, Bipolar Depression and in phase I for Parkinson's disease, but these studies were discontinued because efficacy data did not support pursuing the existing development strategy of stabilization of non-acute patients with schizophrenia.

Pridopidine is an experimental drug candidate belonging to a class of agents known as dopidines, which act as dopaminergic stabilizers in the central nervous system. As a dopamine stabilizer, pridopidine is thought to reduce the effects of dopamine when there’s too much and increase its effects when there’s too little. Pridopidine, therefore, plays two opposing roles in the brain, which stabilize dopamine levels. In this way, pridopidine is thought to help the brain reestablish a normal balance of neurotransmitters, and thus regain control over motion. Pridopidine intended to treat Huntington’s disease movement symptoms. Pridopidine was well tolerated and had an adverse event profile similar to a placebo.

Fluperlapine is dibenzazepine chemically and pharmacologically similar to clozapine. Fluperlapine had no cataleptogenic effect and did not inhibit the apomorphine- and d-amphetamine-induced stereotypes. Fluperlapine is fairly effective neuroleptic drug with a fast-acting antipsychotic affect. The effects in movement disorders imply that fluperlapine is less liable than traditional neuroleptics to induce acute extrapyramidal side effects and tardive dyskinesia and is particularly beneficial in the treatment of patients vulnerable to neurological side-effects. It was demonstrated efficacy in the treatment of a variety of medical conditions including schizophrenia, psychosis associated with Parkinson's disease and dystonia. It has the capacity for producing life-threatening agranulocytosis.

MK-0557, trans-N-[1-(2-fluorophenyl)-3-pyrazolyl]-3-oxospiro [6 azaisobenzofuran-1(3H),10-cyclohexane]-40-carboxamide, is an orally available Neuropeptide Y (NPY5) receptor antagonist. MK-0557 was studied in the clinical trials for the treatment of obesity, however, MK-0557 did not significantly increase the weight loss efficacy. MK-0557 safety and effectiveness were studied in a trial for the treatment of cognitive impairment in patients with schizophrenia. It seems MK-0557 development was discontinued.

Clorotepine (aka octoclothepin or octoclothepine) is an antipsychotic from the tricyclic group derived from perathiepin. It was originally developed in 1965 and marketed in the Czech Republic by Spofa in or around 1971 for the treatment of schizophrenic psychosis. Clorotepine has a high affinity for the dopamine (D1, D2, D3, D4), receptors the serotonin 5-HT (2A, 2B, 2C, 6, 7) receptors, the alpha-adrenergic receptors (1A, 1B, 1D), and the histamine H1 receptors. In most instances, it acts as an antagonist (or inverse agonist). Clorotepine will also block the reuptake of norepinephrine by inhibiting the norepinephrine transporter.

Org 25935 (SCH 900435) is a synthetic drug developed by Organon International, which acts as a selective inhibitor of the glycine transporter GlyT-1. In human trial for prevention of relapse in alcohol-dependent patients in Org 25935 demonstrated no benefit over placebo in preventing alcohol relapse. Org 25935 was tested as an adjunctive treatment to atypical antipsychotics in predominant persistent negative symptoms of schizophrenia, where it did not differ significantly from placebo in reducing negative symptoms or improving cognitive functioning. Clinical trials against panic disorder did not show any benefit compared to placebo.

Belaperidone (LU111995) is a recently identified antipsychotic agent with high 5-hydroxytryptamine2 and dopamine D4 receptor affinities as well as D4 versus D2 receptor selectivity. The drug did not produce catalepsy. LU111995 prolongs the Q-T interval to a limited degree and is not arrhythmogenic over the physiological range of cycle lengths. Belaperidone had been in phase II clinical trials for the treatment of schizophrenia. However, the study about this drug candidate was discontinued.

Fenmetozole is an alpha-2 adrenergic receptor antagonist which was developed for the treatment of schizophrenic and/or depressed patients, however never reached the market. It was also shown that the drug may reduce symptoms of minimal brain dysfunction in children and antagonize the effect of barbiturates and ethanol.