A cross-over design is a type of clinical trial where participants receive multiple treatments in a specific sequence. Each participant acts as their own control, meaning they experience both the treatment and the placebo or alternative treatment. This design helps reduce variability and allows researchers to observe the effects of each treatment more clearly. In a typical cross-over study, participants are randomly assigned to different treatment sequences. After a washout period, where no treatment is given to eliminate lingering effects, they switch to the other treatment. This method is often used in studies involving drugs, dietary interventions, or medical devices.