The pharmacokinetics of venlafaxine in therapeutic doses is well established. It is metabolized by the cytochrome P450 enzymes including CYP2D6. The toxicokinetics in overdose is less well known. Case report: A 33-year-old Caucasian female who ingested 3.0 g venlafaxine, and 210 mg zolpidem. The patient remained symptomatic for the following 24 h. Plasma pharmacokinetic analysis demonstrated a prolonged elimination half-life of venlafaxine, estimated to be 15.3 h. We postulate that the patient was a slow metabolizer of substrates for CYP2D6, an enzyme known to exhibit polymorphism.