The inter-individual variability in drug responses, including ADR, may have diverse causes such as: patient conditions, e.g. a renal dysfunction impacts response to renally excreted drugs; drug interactions, e.g. a first drug, such as fluoxetin may inhibit the effect of a second drug such as tamoxifen by targeting the same enzyme; drug-food interactions e.g. aliments such as grapefruit may inhibit drug metabolism enzymes, such as CYP3A4, causing drug toxicity; genetics e.g. a genomic variation in the coding sequence of a drug metabolizing enzyme such as CYP3A4 also impacts drug response. Here, CYP3A4 is linked to Abnormal renal physiology.