We studied the process that triggers spontaneous recurrences of methamphetamine (MAP) psychosis, a phenomenon known as flashbacks, in 28 female patients who experienced flashbacks, by comparing them with 92 female nonflashbackers with a history of previous MAP psychosis. The study evaluated plasma monoamine neurotransmitter function in 12 of the 28 flashbackers and in 8 of the 92 nonflashbackers. Control data were obtained from 28 normal, healthy females composed of 13 MAP users and 15 nonusers, none of whom became psychotic. The 28 flashbackers had experienced significantly greater frequencies of threatening events and frightening paranoid-hallucinatory states during previous MAP abuse than the 92 nonflashbackers. The dominant triggering factor was a mild fear of other persons. Plasma norepinephrine (NE) levels were significantly higher in the 12 flashbackers during flashbacks than during periods of normalcy and were significantly higher than those in the 13 user and 15 nonuser control subjects. Plasma NE levels in the 12 flashbackers during periods of normalcy were significantly higher than those in the 13 user control subjects. The eight nonflashbackers had significantly higher NE levels than the 13 user control subjects. This suggests that an increase in peripheral noradrenergic activity may be related to the occurrence of flashbacks. The present study suggests that repeated MAP use with frightening experiences may induce sensitivity to psychosocial stressors. A mild fear of other persons may have actualized the encoded frightening memories associated with the frightening experiences via increased sensitivity to psychosocial stressors. Thus, flashbacks may have been caused through an increase in peripheral noradrenergic activity.