Tiospirone (TSP) is an atypical antipsychotic drug. Tiaspirone appeared to be a promising antipsychotic agent as it didn`t cause extrapyramidal syndromes. It has 5HT-2 antagonistic properties as well as affinity for D2, 5HT-1a, 5HT-6 and sigma receptors. Tiospirone was in phase III clinical trials for the treatment of attention hyperactivity disorder with Mead Johnson in the USA but its development appears to have been discontinued.

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.

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.

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.

Mezilamine is a dopamine antagonist, it blocks presynaptic but stimulates postsynaptic alpha-adrenoceptors. Potential antipsychotic drug.

Spiramide (AMI-193) is a spiperone derivative, a selective 5-HT2A, (Ki = 2 nM) 5-HT1A (Ki = 50 nM), and D2 receptor (Ki = 3 nM) antagonist, with negligible affinity for the 5-HT2C receptor (Ki = 4300 nM). The ability of Spiramide to serve as a functional 5-HT2A antagonist in behavioral studies was demonstrated through studies in which Spiramide blocked the discriminative - stimulus effects of the 5HT2A agonist 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM).

Ritanserin (INN, USAN, BAN) is a serotonin receptor antagonist which was never marketed for clinical use but has been used in scientific research. In humans, ritanserin increases deep slow-wave sleep, improved liveliness in a variety of psychiatric disorders and facilitated participation in behaviour therapy. During clinical trials, unexpected observations indicated that ritanserin may be of value in treating obsessive-compulsive disorder, acute mania, negative symptoms of schizophrenia, drug addicts, etc. Clinical observations confirmed the efficacy of ritanserin in the chronic withdrawal phase after detoxification from ethanol. Ritanserin had been in phase III clinical trials by Janssen L.P. for the treatment of anxiety disorder and major depressive disorder. However, the clinical development of ritanserin was discontinued.

Lysergide (LSD) is a semi-synthetic hallucinogen and is one of the most potent drugs known. Recreational use became popular between the 1960s to 1980s, but is now less common. LSD was first synthesized by Albert Hoffman while working for Sandoz Laboratories in Basel in 1938. Some years later, during a re-evaluation of the compound, he accidentally ingested a small amount and described the first ‘trip’. During the 1950s and 1960s, Sandoz evaluated the drug for therapeutic purposes and marketed it under the name Delysid®. It was used for research into the chemical origins of mental illness. Recreational use started in the 1960s and is associated with the ‘psychedelic period’. LSD possesses a complex pharmacological profile that includes direct activation of serotonin, dopamine and norepinephrine receptors. In addition, one of its chief sites of action is that of compound-specific (“allosteric”) alterations in secondary messengers associated with 5HT2A and 5HT2C receptor activation and changes in gene expression. The hallucinogenic effects of LSD are likely due to agonism at 5HT2A and 5HT2C receptors. LSD is also an agonist at the majority of known serotonin receptors, including 5HT1A, 5HT1B, 5HT1D, 5HT5A, 5HT6 and 5HT7 receptors. During the 1960s, LSD was investigated for a variety of psychiatric indications, including the following: as an aid in treatment of schizophrenia; as a means of creating a "model psychosis"; as a direct antidepressant; and as an adjunct to psychotherapy. LSD is listed in Schedule I of the United Nations 1971 Convention on Psychotropic Substances.

Sumanirole is a novel dopamine agonist with high affinity and efficacy at D2 dopamine receptors and has a substantial degree of selectivity for the D2 receptor over other dopamine receptor subtypes. It had been in clinical trials for the treatment of Parkinson’s disease and restless leg syndrome but these studies were terminated for the efficacy reason.