Mark Ruscin, PharmD, FCCP, BCPS, Southern Illinois University Edwardsville School of Pharmacy; Sunny A Linnebur, PharmD, BCPS, BCGP, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Reviewed / Revised Jul 2021 | Modified Sep 2022 View Patient Education Topic Resources Effect of Aging on Drug Response In contrast to pharmacokinetic effects, pharmacodynamics is defined as what the drug does to the body or the response of the body to the drug; it is affected by receptor binding, postreceptor effects, and chemical interactions (see Drug-Receptor Interactions).