Relenopride (YKP-10811) is a serotonin 4 (5-HT4) receptor agonist that was developed for regulation of gastric motility. It improved antral contractions and accelerated gastric emptying in dogs and had no adverse effects. Phase II clinical trials have investigated the efficacy and safety of relenopride in patients with (chronic and functional) constipation and irritable bowel syndrome (IBD). Relenopride was reported to accelerate gastrointestinal motility and colonic transit and improve bowel functions in patients with functional constipation, compared with placebo.

FLESINOXAN, a phenylpiperazine derivative, is a selective agonist for 5-HT1A receptors. It is an antidepressant agent which clinical development was stopped.

Piclozotan (SUN N4057) is a 1,4-benzoxazepine derivative that exhibits sub-nanomolar affinity at serotonin 1A receptor with good selectivity over dopamine D2 and α1-adrenoceptors. Piclozotan reduced levodopa-induced forelimb hyperkinesia by 55% and 69%, respectively, at 1h relative to the control. Piclozotan significantly lengthened the duration of rotational behavior by 26% versus the control and attenuated the increase in striatal levodopa-derived extracellular dopamine levels. Piclozotan, a serotonin 1A agonist, can improve motor complications in patients with advanced Parkinson's disease. Piclozotan has been shown to be neuroprotective against ischemic neuronal damage in animal models. Piclozotan had been in phase II for the treatment of stroke. However, this research has been discontinued.

Repinotan (BAYX3702) is a highly selective 5-HT1A receptor agonist that has shown neuroprotective effects in animals (attenuating NMDA-induced delayed neuronal death in rats). Repinotan inhibits glutamate induced depolarization. A variety of mechanisms and pathways is thought to be involved in its efficacy, such as activation of the anti-apoptotic phosphatidylinositol 3-kinase (PI-3K) pathway, inhibition of glutamate release, extracellular-regulated kinase (Erk)-stimulated Bcl-2 expression or inhibition of caspase-3 activity, and increased release of the neurite extension factor S-100 beta. Based on results in animal studies, repinotan could be a promising candidate for treating acute ischemic stroke in humans. A phase II clinical trials in patients with acute ischemic stroke was completed in 2009.

Pardoprunox is a partial D2/3 dopamine receptor agonist and full 5-HT1A serotonin receptor agonist. Partial D(2/3) dopamine (DA) receptor agonists provide a novel approach to the treatment of the motor symptoms of Parkinson's disease that may avoid common dopaminergic side effects, including dyskinesia and psychosis. Pardoprunox passed phase III clinical trial for the treatment of Parkinson's disease.

Pumosetrag is a novel, orally active and selective 5-HT 3 agonist. It is a partial agonist in rats and guinea-pig and a full agonist in the mouse, suggesting important species differences in 5-HT3 receptor structure. Pumosetrag had been in phase II clinical trials for the treatment of gastroesophageal reflux disease and irritable bowel syndrome. No serious adverse events were reported. Diarrhea was not more common on the drug and only one subject experienced pruritus. All researches on this drug candidate are discontinued.

Disulergine is the synthetic 8 alpha-amino ergoline. Disulergine is the dopamine D2 receptor agonist and prolactin release inhibitor. Disulergine was as potent as dopamine in inhibiting growth hormone release but, in contrast to dopamine, was nearly ineffective in stimulating the secretion of the hormone.

Osemozotan (also known as MKC-242) was developed as a selective 5-HT1A receptor agonist. Experiments on animal have shown that osemozotan improved most abnormal behaviors such as isolation rearing. Osemozotan was being investigated for the treatment of pain, aggressive behavior, anxiety, depression, obsessive-compulsive disorder, and drug dependence with methamphetamine and cocaine. However, all these studies were suspended. In the USA osemozotan participated in phase II clinical trial for the insomnia patients, however, the study was terminated because of the license agreement.

Avitriptan (BMS-180048), a new 5-HT 1B/1D receptor agonist, has been studied in phase II clinical trials in patients with migraine headaches. Later experiments have confirmed antimigraine activity together with coronary side-effect potential that is why further studies were discontinued.

Lirexapride serotonin 5-HT4 receptor and dopamine D2 receptor agonists. It had been in phase II clinical trials for the treatment of irritable bowel syndrome. However, this research has been discontinued.