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with INR 6.4, 39 days after stopping warfarin, factors II, VII, and X had low values; LFTs and fibrinogen remained normal. On day 94, duloxetine was stopped, and by day 98, INR had fallen to 1.2, with factor II increasing to 48% and factor X to 54%. On day 105, INR was 0.9. The metabolism of warfarin involves several CY P450 isoenzymes (CY P 1A2, 2D6, 2C9, 2C19, and 3A4). Duloxetine inhibits CYP1A2 and CYP2D6 and could potentially interact with warfarin. Duloxetine is also highly protein bound in plasma (> 90%) and when given with warfarin, another highly protein-bound drug, could displace warfarin, possibly resulting in a toxic effect. Our case emphasizes the need to closely monitor for the toxic drug interactions between the 2 drugs.