Adaptive clinical trial designs have been proposed as a promising new approach that may help improve the drug discovery process. Recent statistical papers have introduced a variety of methods to allow unplanned interim modifications to the study design while preserving the type I error rate of the clinical trial. In particular, there is a large body of literature exploring designs with unplanned modifications to the sample size based on interim estimates of the treatment effect falling into a “promising zone”. In this module we present the impact such designs can have on the power of randomized clinical trials. We provide guidance on the adaptive rules that lead to the greatest benefit to study precision, and we present and compare methods for full statistical inference following the use of such designs.