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.

MK-212 is a 5HT2C-receptor agonist. It displays selectivity for 5-HT2C over 5-HT2A (IC50 values are 0.028 and 0.42 uM for human 5-HT2C and 5-HT2A receptors expressed in HEK293 cells respectively). A dose-dependent the effect of 5HT2C-receptor agonist MK-212 on mouse behavior was demonstrated. Intraperitoneal injection of MK-212 in high doses (0.5 and 1.0 mg/kg) increased blood level of corticosterone in mice and reduced their motor activity. In low doses of 0.1 and 0.2 mg/kg, the agonist reduced anxiety, but had no effect on motor activity. It is hypothesized that low doses of MK-212 exhibited anxiolytic activity in mice.

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.

Pirenperone, a quinazoline derivative, is a selective antagonist at serotonin receptor 2A binding sites. The liposoluble compound pirenperone has been studied in a variety of behavioral tests including the sensitive d-lysergic acid diethylamide (LSD) cue discrimination assay, in which it served as a potent LSD-antagonist. Pirenperone also proved to be an effective antagonist of serotonin-mediated behavioral responses including the head twitch response thought to be mediated by serotonin receptors.

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.

Quizapine is a piperazine-based nonselective serotonin (5-HT) receptor agonist with antidepressant and oxytocic activities. Quipazine targets and binds to serotonin receptors, particularly to the 5HT2A and 5HT3 receptors. Quipazine is a potential anti-parkinsonian agent. Serotonin receptor activation by quipazine may lead to smooth muscle contraction and antidepressant effects. quipazine, a central serotonergic agent, counteracted some of the drug-induced symptoms of pseudoparkinsonism in laboratory animals. Cholinergic, dopaminergic and histaminergic receptors play an important role in the manifestations of these symptoms.

ORG 37684 is a selective full agonist of 5-hydroxytryptamine receptor 5-HT2 family with a high selectivity for 5-HT2C in comparison with 5-HT2B and 5-HT2A receptors. It was studied for treatment of depression, but that investigations were discontinued. On animal studies ORG 37684 possessed hypophagic effect, which was exclusively mediated by activation of 5-HT2C receptors. Thus, this compound can be further investigated in using for weight loss.