WinNonlin is a software program used in pharmacokinetic analysis. It helps analyze drug concentration–time data and calculate important pharmacokinetic parameters such as the area under the curve (AUC), maximum drug concentration (Cmax), time to reach maximum concentration (Tmax), and half-life (t½). The software also supports non-compartmental analysis (NCA), making it a useful tool in bioequivalence studies, and clinical pharmacology.