Drug half-life has important implications for dosing regimen and peak-to-trough ratio at the steady state. A half-life of 12-48 h is generally ideal for once daily dosing of oral drugs. If the half-life is too short, it may require more frequent dosing in order to maintain desired exposures and avoid unnecessarily high peak concentrations. This may pose challenges to achieving optimal efficacy, safety, and patient compliance. If the half-life is too long, the time over which accumulation and subsequent elimination occur may be prolonged. This may pose problems with managing adverse effects and the design of efficient clinical trials. Half-life is a key parameter for optimization in research and development. Structural modification to affect clearance, and to a lesser extent volume of distribution, is the preferred means of modulating half-life. An effective approach to half-life optimization requires an understanding of the many pitfalls associated with its estimation and interpretation.