p-Methylthioamphetamine (MTA) is a potent and selective serotonin releaser that appears to lack the serotonin neurotoxic effects seen with p-chloroamphetamine (PCA). MTA was about twice as potent as PCA at inhibiting serotonin uptake, but 7 to 10 times less potent at inhibiting dopamine and norepinephrine uptake. In drug discrimination tests, MTA was nearly as effective as PCA in animals trained to recognize MDMA or related compounds. MTA also caused dose-dependent serotonin release from rat brain slices similar to PCA. However, a high dose of PCA reduced serotonin and its metabolite by 70-90% in brain regions, while twice the molar dose of MTA had no such effect, suggesting MTA is not neurotoxic to serotonin neurons.
MMAI (5-methoxy-6-methyl-2-aminoindan) appears to be a selective serotonin releaser without psychostimulant or hallucinogenic effects. In rats trained to discriminate MMAI from saline, only other serotonin-releasing drugs fully mimicked MMAI's effects. MMAI did not produce amphetamine-like or LSD-like stimulus effects. Depleting serotonin with p-chlorophenylalanine blocked MMAI's discriminative cue for about a week, and selective serotonin reuptake inhibitors reduced its discriminability. Behavioral observations showed MMAI induced a syndrome similar to that caused by serotonin precursors or receptor agonists, including hypolocomotion, catalepsy-like posture, and flat body posture. The findings suggest MMAI acts primarily by releasing serotonin rather than directly activating or blocking neurotransmitter receptors.