A numerical model for transdermal drug delivery (TDD) has been developed by treating skin as a composite, dynamic, porous medium. Governing unsteady mass transport equations in porous medium was solved for different cases for up to a period of drug-patch application of 10 hrs. The effects of cell migration and anisotropic diffusive properties of stratum corneum (SC) on TDD are analyzed. Each of the above factors and their combination are found to significantly affect TDD. The cell migration in SC decreases the predicted amount of drug considerably. Their combined effect in TDD helped in identifying four distinct regimes of pharmacological as well as engineering importance within the domain.