The Alzheimer's Disease Anti-inflammatory Prevention Trial (ADAPT) is designed to compare two nonsteroidal anti-inflammatory agents against placebo. A placebo control for two active treatments can be achieved in several ways, each of which may have different implications for the logistics of drug supply, enrollment, adherence to treatment, and the validity of specific treatment comparisons. The authors outline the placebo designs considered in ADAPT, discuss their advantages and disadvantages, and provide their rationale for and the consequences of the selection of the double placebo design.