Clozapine, an often-prescribed antipsychotic drug, is implicated in severe adverse drug reactions (ADRs).Formation of reactive intermediates by cytochrome P450s (CYPs) has been proposed as a possible expla-nation for these ADRs. Moreover, a protective role for human glutathione S-transferases (hGSTs) wasrecently shown using purified enzymes. We investigated the interplay between CYP bioactivation andGST detoxification in a reconstituted cellular context using recombinant yeast expressing a bacterialCYP BM3 mutant (M11), mimicking the drug-metabolizing potential of human CYPs, combined withhGSTA1-1, M1-1 or P1-1. Clozapine and the N-desmethylclozapine metabolite caused comparable growthinhibition and reactive oxygen species (ROS) formation, whereas the clozapine-N-oxide metabolite wasclearly less toxic. Clozapine metabolism by BM3 M11 and the hGSTs in yeast was confirmed by iden-tification of stable clozapine metabolites and hGST isoform-specific glutathione-conjugates. Oxidativemetabolism of clozapine by BM3 M11 increased ROS formation and growth inhibition. Co-expression ofhGSTP1-1 protected yeast from BM3 M11 induced growth inhibition in presence of clozapine, whereassimilar expression levels of hGSTA1-1 and hGSTM1-1 did not. ROS formation was not lowered by hGSTP1-1 co-expression and was unrelated to mitochondrial electron transport chain (mETC) activity. We presenta novel cellular model to study the effect of CYP and GST interplay in drug toxicity.