To speed up and make less expensive the typically very expensive and time-consuming drug development process, numerous computational tools have been developed. Preclinical studies involve estimating absorption, distribution, metabolism, and excretion (ADME) properties and optimizing new chemical entities. Issues with these pharmacokinetic properties, as well as toxicity, have been part of the reasons for failure of drug candidates. All these properties affect the pharmacodynamic action of a drug molecule. A good candidate should have balanced ADME and good potency. This mini-review discusses the impact of tautomerism on pharmacokinetics, pharmacodynamics properties, formulation, and racemization. We emphasize here that tautomerism is not a novel phenomenon of drugs in the pill or the body.