(+)-alpha-Dihydrotetrabenazine (HTBZ) is an active component of tetrabenazine. Tetrabenazine is a mixture of closely-related compounds (isomers) and is readily metabolized in the human body to HTBZ and related isomers. Tetrabenazine is a drug for the symptomatic treatment of hyperkinetic movement disorder and is marketed under the trade names Nitoman in Canada and Xenazine in New Zealand and some parts of Europe, and is also available in the USA as an orphan drug. (+)-alpha-Dihydrotetrabenazine and related benzo[a]quinolizines have been labeled with tritium and carbon-11 radioisotopes and used for in vitro and in vivo studies of the VMAT2 in animal and human brain. Adeptio Pharmaceuticals is developing alpha-dihydrotetrabenazine (HTBZ) for the treatment of neurological disorders. It acts by inhibiting vesicular monoamine transporter 2 (VMAT2), thereby blocking the transport of dopamine into axon terminals or into storage vesicles.

Clozapine was discovered in 1958 by an anesthetist and now it is used for the treatment of schizophrenia. Although the exact mechanism of its action is unknown, the effect of clozapine on schizophrenia is associated with inhibition of dopamine D2 and serotonin 2A receptors.

DA-6886 is an antagonist of the 5-HT4 receptor, discovered by the Korean Dong-A ST Research Institute. The drug binds with high activity and selectivity to human 5-HT4 receptor splice variants, with mean pKi of 7.1, 7.5 and 7.9 for the human 5-HT4a, 5-HT4b, and 5-HT4d, respectively. DA-886 induced relaxation of the rat esophagus preparation in a 5-HT4 receptor antagonist-sensitive manner. In the normal ICR mice, oral administration of the drug at 0.4 and 2 mg/kg resulted in a marked stimulation of colonic transit. DA-6886 was investigated in phase I clinical trial for the treatment of Irritable Bowel Syndrome.

Juvantia Pharma and Orion developed ORM-12741, also known as ORM-10921, a novel selective antagonist of alpha-2C adrenoceptors for the treatment of depression and Alzheimer's disease. ORM-12741 participated in phase II clinical trial where was evaluated the safety and efficacy of the drug in patients with Alzheimer's disease. In spite of the successfully completed phase II, further study of the drug for this disease was discontinued. In addition, ORM-12741 participated in clinical trial phase II to prove the concept that this drug could prevent blood vessel spasms for Raynaud's phenomenon. Raynaud's phenomenon is a disorder of the digital blood vessels resulting in episodic impairment of blood flow. However, this study was terminated because of the recommendation by study Data and Safety Monitoring Committee to the sponsor following the interim analysis of 8 subjects.

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.