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.

Napamezole [WIN 51181] is a potent alpha-2 adrenergic receptor antagonist and a selective inhibitor of 5-hydroxytryptamine re-uptake in vitro. Napamezole was at the phase I stage of development with Sanofi Winthrop (formerly known as Sterling Drug before it was purchased by Sanofi) in the USA as a treatment for depression. The alpha adrenergic antagonist activity of napamezole was determined in vitro in rat brain receptor binding assay using [3H]clonidine and [3H]prazosin for alpha-2 and alpha-1 receptors, respectively. The Ki values for napamezole were 28 nM (alpha-2) and 93 nM (alpha-1).

Gepirone (brand name Travivo) is an investigational azapirone antidepressant and anxiolytic drug in development for the treatment of major depressive disorder but has yet to be marketed. Like other azapirones, it acts as a selective partial agonist of the 5-HT1A receptor. Gepirone has been under development in the U.S. in an extended release form (referred to as Gepirone ER). It has been rejected multiple times by the FDA during the drug approval process and Phase III studies evaluating its use in the treatment of MDD were prematurely terminated. These were the initial Phase III studies of gepirone ER in MDD, and the effective dose range had not been determined. In March 2016, the FDA reversed its decision and gave gepirone ER a positive review, clearing the way for the drug to finally gain market approval in the U.S. In addition to its antidepressant and anxiolytic properties, gepirone has been found to improve symptoms of sexual dysfunction in men and women, similarly to the marketed 5-HT1A receptor agonist flibanserin. The pro-sexual effects appear to be independent of its antidepressant and anxiolytic effects. Mechanism of action studies have demonstrated that gepirone possesses a much greater selectivity for 5-HT1A receptors over dopamine D2 receptors. Long-term studies have shown that gepirone has a differential action at presynaptic (agonist) and post-synaptic (partial agonist) 5-HT1A receptors. Treatment with gepirone ER desensitizes presynaptic 5-HT1A receptors, which decreases serotonin autoregulatory inhibition and enhances activation of postsynaptic 5-HT1A receptors. As a partial agonist gepirone ER acts as an agonist when endogenous serotonin is not present and as an antagonist when endogenous serotonin is present. Overall, gepirone ER increases serotonin production when insufficient amounts are present, and decreases serotonin production when excess amounts are present. Gepirone has been tested in Phase II clinical trial as antidepressant medication for pharmacotherapy for cocaine dependent subjects.

Lorcaserin, currently marketed under the trade name Belviq and previously Lorqess during development, is a weight-loss drug developed by Arena Pharmaceuticals. Lorcaserin is a selective 5-HT2C receptor agonist, and in vitro testing of the drug showed reasonable selectivity for 5-HT2C over other related targets. 5-HT2C receptors are located almost exclusively in the brain, and can be found in the choroid plexus, cortex, hippocampus, cerebellum, amygdala, thalamus, and hypothalamus. The activation of 5-HT2C receptors in the hypothalamus is supposed to activate proopiomelanocortin (POMC) production and consequently promote weight loss through satiety. This hypothesis is supported by clinical trials and other studies. While it is generally thought that 5-HT2C receptors help to regulate appetite as well as mood, and endocrine secretion, the exact mechanism of appetite regulation is not yet known. Lorcaserin has shown 100x selectivity for 5-HT2C versus the closely related 5-HT2B receptor, and 17x selectivity over the 5-HT2A receptor

Dexfenfluramine, also marketed under the name Redux, is a serotoninergic anorectic drug. Dexfenfluramine, the dextrorotatory isomer of fenfluramine, is indicated for use in the management of obesity in patients with a body mass index of > or = 30 kg/m2, or > or = 27 kg/m2 in the presence of other risk factors. Unlike fenfluramine, dexfenfluramine is a pure serotonin agonist. Dexfenfluramine increases serotonergic activity by stimulating serotonin (5-hydroxytryptamine; 5-HT) release into brain synapses, inhibiting its reuptake into presynaptic neurons and by directly stimulating postsynaptic serotonin receptors. Dexfenfluramine reduces blood pressure, percent glycosylated hemoglobin, and concentrations of blood glucose and blood lipids, but these benefits may be indirect. Dexfenfluramine may also be of some value in controlling eating habits in diabetic patients, preventing weight gain after smoking cessation, and treating bulimia, seasonal affective disorder, neuroleptic-induced obesity, and premenstrual syndrome. Dexfenfluramine's most frequent adverse effects are insomnia, diarrhea, and headache; it has also been associated with primary pulmonary hypertension. The drug should not be combined with other serotonergic agonists because of the risk of serotonin syndrome. The recommended dosage is 15 mg twice daily. Dexfenfluramine is effective in the treatment of obesity in selected patients. Because its efficacy is lost after six months of continuous treatment, it should be viewed primarily as an adjunct to diet and exercise. Dexfenfluramine was approved by the FDA in 1996 and has been widely used for the treatment of obesity. However, Dexfenfluramine was removed from the U.S. market in 1997 following reports of valvular heart disease and pulmonary hypertension.

Roxindole (EMD-49,980) is a dopaminergic and serotonergic drug which was originally developed for the treatment of schizophrenia. Roxindole has also been investigated as a therapy for the major depressive disorder, Parkinson's disease, and prolactinoma. Roxindole is dopamine autoreceptor-selective agonistic drug with high affinity to D2-like receptors and with much lower affinities to D1-like, % and ol2, muscarinic and 5HT 2 receptors. Additionally, Roxindole exerts 5HT uptake inhibition and 5HT1A agonistic effects. The bioavailability of Roxindole has been estimated at 5% due to a high first-pass metabolization. On the other hand, in 14C distribution studies, Roxindole has crossed the blood-brain barrier readily and the brain concentrations at all intervals have been much higher than corresponding plasma levels. In clinical trials, Roxindole ‘s antipsychotic efficacy was only modest but it was unexpectedly found to produce potent and rapid antidepressant and anxiolytic effects. However, the clinical development of Roxindole was discontinued.

Medifoxamine, an antidepressive drug, preferentially inhibits dopamine reuptake. It was marketed in France, but because of the hepatotoxicity, then was withdrawn.

Alniditan is a non-indole migraine-abortive agent. It is a benzopyran derivative The action of sumatriptan is thought to be mediated by 5-hydroxytryptamine (5-HT)1D-type receptors. Alniditan did not attenuate substance P-induced inflammation, suggesting that the mediating receptors are located prejunctionally. In vitro alniditan exhibited less vasoconstrictive effects on the rat basilar artery than did sumatriptan, although at a very high concentration, alniditan caused intensive constriction, most likely through a mechanism independent from 5-HT receptor activation. Alniditan dose dependently attenuated the neurogenic inflammation and was more potent than sumatriptan. Adverse effects are: head pressure, paraesthesia, and hot flushes.

Zalospirone is a selective partial agonist of 5HT1A receptor developed by Wyeth. It was investigated in clinical trials in major depression. Although the highest dose of the drug seemed to have significant antidepressant efficacy, it was not well tolerated and by the 6th week more than half of patients in the high-dose group has dropped out.

Sediel (generic name: tandospirone citrate, marketed as Sediel in Japan) is a new type of antianxiety drug developed independently by Sumitomo Pharmaceuticals. It acts selectively on only the serotonin nerves in the brain that play an important part in the formation of anxiety and depression, and demonstrates antianxiety and anti-depression effects. Since it does not act on the other nerves that are so extensive in the brain, there is virtually no hypnotic or sedative effect, and the drug displays virtually no drug-dependence or side effects such as drowsiness and dizziness. Sediel has been on sale in Japan since December 1996, and is recognized for recognized as effective in the treatment of generalized anxiety disorders. Tandospirone acts as a potent and selective 5-HT1A receptor partial agonist. It was also investigated the usefulness of 5-HT1A agonists for enhancing some types of cognitive performance and possibly social and work function in patients with schizophrenia, and related to this was discovered, that tandospirone in combination with atypical antipsychotic drugs can improve cognitive function in Schizophrenia.