Synthetic cathinones inhibit monoamine transporters, such as serotonin, norepinephrine, and dopamine transporters, and act on the central nervous system via increasing synaptic concentrations of monoamines. These compounds, which are highly addictive and potentially poisonous, are new psychoactive substances. In this study, we investigated the toxicokinetics of the synthetic cathinone, α-pyrrolidinohexanophenone (α-PHP), and assessed the relationship between the toxicokinetics and the long-term clinical symptoms induced by α-PHP in a male patient. The patient (39 years old) suddenly started uttering inarticulate words and demonstrating incomprehensible behavior in his house, and was brought to the emergency department of Iwate Medical University hospital. He presented with psychotic symptoms, such as hallucinations and delusion; however, his vital signs were normal. The hallucinations and delusion improved by the third day of hospitalization. Toxicological analysis was performed using liquid chromatography-tandem mass spectrometry with QuEChERS extraction. α-PHP was detected in his serum at a concentration of 175 ng/mL on his arrival at the hospital. His serum concentrations of α-PHP were serially determined and their natural logarithms were plotted against time after arrival. Although serum concentrations at early time points were lacking, the obtained curve was consistent with a two-compartment model and indicated a serum elimination half-life of 37 h. The long-lasting psychotic symptoms induced by synthetic cathinones appear to be correlated with their toxicokinetic characteristics, such as their long half-lives. Finally, interpreting the toxicokinetics of synthetic cathinones may provide useful information for the toxicological assessment of new psychoactive substances for forensic and clinical purposes.