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.

Amphetamine is a potent central nervous system (CNS) stimulant that is used in the treatment of attention deficit hyperactivity disorder (ADHD), narcolepsy, and obesity. Amphetamine was discovered in 1887 and exists as two enantiomers: levoamphetamine and dextroamphetamine. The mode of therapeutic action in ADHD is not known. Amphetamines are thought to block the reuptake of norepinephrine and dopamine into the presynaptic neuron and increase the release of these monoamines into the extraneuronal space. At higher dosages, they cause release of dopamine from the mesocorticolimbic system and the nigrostriatal dopamine systems. Amphetamine may also act as a direct agonist on central 5-HT receptors and may inhibit monoamine oxidase (MAO). In the periphery, amphetamines are believed to cause the release of noradrenaline by acting on the adrenergic nerve terminals and alpha- and beta-receptors. Modulation of serotonergic pathways may contribute to the calming affect. The drug interacts with VMAT enzymes to enhance release of DA and 5-HT from vesicles. It may also directly cause the reversal of DAT and SERT. Several currently prescribed amphetamine formulations contain both enantiomers, including Adderall, Dyanavel XR, and Evekeo, the last of which is racemic amphetamine sulfate. Amphetamine is also prescribed in enantiopure and prodrug form as dextroamphetamine and lisdexamfetamine respectively. Lisdexamfetamine is structurally different from amphetamine, and is inactive until it metabolizes into dextroamphetamine.