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.

Spiroxatrine is a drug which acts as a selective antagonist at both the 5-HT1A receptor and the α2 adrenergic receptor. Spiroxatrine was identified as a moderately potent but non-selective agonist at the human nociceptin/orphanin FQ receptor, ORL1

Mesulergine, an antagonist of 5-HT2C, and dopamine receptors was studied in clinical trials for the treatment of Parkinson's disease. However, further, development was discontinued due to toxicological observations in animal experiments.

Aplindore (DAB-452) is a small molecule that displays potent dopamine D2 receptor partial agonist activity in in vitro and in vivo assays and is predicted to have antipsychotic efficacy without motor side effects. Aplindore had been in phase II clinical trials for the treatment of Parkinson's disease and restless legs syndrome. Aplindore was generally well tolerated and there were no withdrawals due to adverse events and no serious adverse events.

Ocaperidone [R 79598] is an equipotent antagonist of central dopamine D2 and serotonin2 receptors being investigated as a potential antipsychotic agent. Ocaperidone is a benzisoxazol piperidine antipsychotic primarily binds and with high affinity to 5-HT2 (serotonin) receptors, alpha1 and alpha 2 adrenergic receptors, dopamine D2 receptors and histamine H1 receptors. Ocaperidone is an antagonist primarily at the 5HT and D2 receptors. A proposed mechanism of action is the central D2 receptor blockade which is common to all neuroleptics that are used to treat positive symptoms of schizophrenia.

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.

Eptapirone is a potent, selective and efficacious 5-HT1A receptor agonist. In rats, it is readily bioavailable after oral administration. Likely, because of its high efficacy at 5-HT1A receptors, Eptapirone exerted powerful antidepressant- and anxiolytic-like activity in animal models. Eptapirone given in the evening suppresses REM (rapid eye movement) sleep more than buspirone and implies a greater central effect on serotonin receptors, which is consistent with the preclinical data that indicate it has greater efficacy than buspirone. It has little effect on other sleep stages. Eptapirone has been in phase I clinical trials for the treatment of anxiety and major depressive disorder. However, this research has been discontinued.

U-92016A is a psychoactive drug and research chemical used in scientific studies. U-92016A acts as a potent, high efficacy, and selective 5-HT1A receptor full agonist with a long duration of action.