Neurotoxicity of the amphetamine analogs methamphetamine (METH) and 3,4-methylenedioxyamphetamine (MDA) (the active metabolite of ecstasy) may involve their prostaglandin H synthase (PHS)-dependent bioactivation to free radical intermediates that generate reactive oxygen species and oxidatively damage cellular macromolecules. We used Chinese hamster ovary-K1 (CHO-K1) cell lines either untransfected or stably expressing human PHS-1 (hPHS-1) or hPHS-2 to investigate hPHS isozyme-dependent oxidative damage and cytotoxicity. Both METH and MDA (250-1000 μM) caused concentration-independent cytotoxicity in hPHS-1 cells, suggesting maximal bioactivation at the lowest concentration. In hPHS-2 cells, with half the activity of hPHS-1 cells, METH (250-1000 μM) cytotoxicity was less than that for hPHS-1 cells but was concentration dependent and increased by exogenous arachidonic acid (AA), which increased hPHS activity. Whereas 10 μM MDA and METH were not cytotoxic, at 100 μM both analogs caused AA-dependent and concentration-dependent increases in cytotoxicity and DNA oxidation in both hPHS-1/2 cells. The hPHS-2 isozyme appeared to provide more efficacious bioactivation of these amphetamine analogs. Acetylsalicylic acid, an irreversible inhibitor of both hPHS-1 and hPHS-2, blocked cytotoxicity and DNA oxidation in both cell lines and untransfected CHO-K1 cells lacking PHS activity were similarly resistant. Accordingly, isozyme-dependent hPHS-catalyzed bioactivation of METH and MDA can cause oxidative macromolecular damage and cytotoxicity, which may contribute to their neurotoxicity.