Paroxetine is generally dosed at 20–50 mg/day in single doses. Blood levels corresponding to a dose of 20 mg/day are 23–75 ng/ml. A 50-mg dose can produce blood levels as high as 207 ng/ml. The blood levels of our patient were about 10 times higher than the expected mean at that dose. Paroxetine is metabolized by the cytochrome P450 2D6 system, and the drug itself is an inhibitor of the enzyme. This results in a nonlinear metabolism, with higher doses causing a noncorresponding increase in the blood levels of the drug. Also, almost 7%–10% (1) of the white population has diminished 2D6 activity and consequently relies on unknown mechanisms for the metabolization of the drug. Dosing is guided by the clinical response; most patients improve in this dose range, and drug levels are rarely drawn.