Participating in several trials at the same time can put your life at risk because of drugs interaction. Safety issues are the main reason why most clinical trials will not allow volunteers to start a new trial unless they are out of their exclusion period from the previous trial. The exclusion period also called the “wash-out period,” is usually 30 days but can be longer depending on how long the human body will take to eliminate a specific drug. The exclusion period is validated by the health authorities and is known before the start of the study. The other reason is for the clinical trial itself as it is not possible to analyze specific drug safety and efficiency when a volunteer has a cocktail of drugs in his body.