Setoperone is and antagonist of the brain serotonin 5-HT2 receptor and particular the 5-HT2A isoform. Setoperone is radiolabeled with the radioisotope fluorine-18 and is used in positron emission tomography (PET) in neuroimaging for the study neuropsychiatric disorders, such as schizophrenia and depression.

Adoprazine (SVL-313) is a full 5-HT1A receptor agonist and full D2/3 receptor antagonist possessing characteristics of an atypical antipsychotic, representing a potential novel treatment for schizophrenia and bipolar disorder. This drug together with some others, e.g. Mazapertine succinate, PF-217830 was discontinued from clinical trials due to either non-optimal pharmacokinetic properties or insufficient therapeutical efficacy.

Butaclamol is an antipsychotic drug, which was studied for the treatment of schizophrenia. This drug has never marketed and now is used in research, because of its action as a dopamine receptor-blocking agent. Butaclamol consists of the two forms: (-)-butaclamol, an inactive drug and (+)-butaclamol, a potent neuroleptic drug.

PF-03654746 is a potent, selective antagonist of the human H3 receptor, developed by Pfizer. It was in the clinical trial phase II for the treatment of excessive daytime sleepiness (EDS) associated with narcolepsy, Tourette syndrome as well as potential anti-allergy applications and in phase I of clinical trial for the treatment of Schizophrenia and Alzheimer's disease, but these investigations were discontinued.

Talnetant (SB-223412) is a selective, orally active neurokinin 3 receptor antagonist and is under development for the potential treatment of several disorders, including irritable bowel syndrome, schizophrenia, chronic obstructive pulmonary disease, cough, overactive bladder and urinary incontinence. The most common adverse effects were headache, fatigue, and nausea.

Fananserin is a potential antipsychotic compound with a high affinity for both D4 and 5-HT2A receptors, and negligible affinity for D2 receptors. Fananserin has been researched for the treatment of schizophrenia. Fananserin was the first selective D4/5-HT2A antagonist to undergo clinical trials for schizophrenia. It has a high affinity for D4 (Ki 2.9 nM) and 5-HT2A (Ki 0.37 nM) receptors and is over 100-fold selective versus H1, a1 adrenergic, 5-HT1A and D2 dopamine receptors. Development of this compound was halted following phase II clinical trials due to lack of efficacy.

Iomazenil (also known as Ro16-0154, benzodine) is a partial inverse agonist of central-type benzodiazepine receptors (BZR) which binds specifically to BZR with high affinity and a potential treatment for alcohol abuse. The compound was introduced in 1989 by pharmaceutical company Hoffmann-La Roche as an Iodine-123-labelled SPECT tracer for imaging benzodiazepine receptors (GABAA receptors) in the brain.

Sonepiprazole exhibits highly specific binding to the D4 dopamine receptor with more than 100-fold selectivity for the D4 receptor over other receptors, including dopamine, serotonin, and adrenergic receptors. It is a neutral antagonist at the D4 dopamine receptor and is devoid of dopamine agonist activity. Sonepiprazole selectively induces c-fos expression in the prefrontal cortex and blocks behavioral, biochemical, and genomic effects of repeated amphetamine administration in rats. Sonepiprazole was investigated as an antipsychotic for the treatment of schizophrenia in a placebo-controlled clinical trial, but in contrast to its comparator olanzapine no benefits were found and it was not researched further for this indication.

ACP-104 or N-Desmethylclozapine (NDMC), or norclozapine is a major metabolite of clozapine, which was developed like a small molecule drug candidate by ACADIA for treatment schizophrenia. ACP-104 combines M1 muscarinic agonist, 5-HT2A inverse agonist, and D2 and D3 dopamine partial agonist in a single compound and, therefore, uniquely addresses what ACADIA believed are the three most promising target mechanisms for treating schizophrenia. Then drug was discontinued, because the study did not meet its primary endpoint of antipsychotic efficacy or any of the secondary endpoints. Neither dose of ACP-104 demonstrated improved efficacy as compared to placebo. The most common adverse events in the treatment arms relative to placebo were increased salivation, tachycardia, and dyspepsia, which were noted to be dose-related. There was no clinically significant decrease in neutrophil counts in the study drug arms.

CX 516, a compound synthesized by Cortex Pharmaceuticals using Ampakine® technology licensed from the University of California, was in clinical investigations for the treatment of Alzheimer's disease, schizophrenia, fragile X syndrome and autism, and sleep disorders, however, development of this drug candidate has been discontinued. CX 516 had an extremely short halflife in humans, very low potency and failed to show any benefits in phase II studies. The compound did have a good safety profile, reducing concerns about the toxicity of excess glutamate. Cortex subsequently terminated clinical development of CX 516.