Paramethoxymethamphetamine (PMMA) is an emerging and prevalent psychoactive drug with a structure analogous to amphetamine and related psychostimulants. However, the neurobehavioral effect is only studied in experimental animals and is barely mentioned in human. The authors report the antemortem neurobehavioral manifestations in 8 patients with PMMA use. There were 2 different antemortem presentations. The first group of patients showed delirium, hypertalkativity, and incoherence speech and then turned into convulsion and death. They did not exhibit the typical hyperdopaminergic movement disorder. The second group of patients gradually fell asleep and then suffered respiratory or cardiovascular collapse. The heart blood PMMA level was higher in the second group than in the first group of patients. Forensic autopsy showed variable findings, ranging from no remarkable change to significant pathological damage similar to serotonin syndrome in both groups of patients. PMMA seems to enhance serotoninergism than dopaminergism, and exerts a concentration-related dual effect on human.