In this article we describe the developments of two patients who were hospitalized after a quetiapine overdose, subsequently developing delirium. Delirium occurred several hours after ingestion and lasted several days. Laboratory blood testing revealed a slower decline in quetiapine plasma concentration than expected when compared to the standardized half-life averages of therapeutic doses of quetiapine. The clinical state during the first hours after ingestion does not sufficiently predict further clinical outcome. The changes in pharmacokinetics due to the intoxication, so-called toxicokinetics, are the underlying cause.