Exploratory toxicology as an integrated part of drug discovery. Part I: Why and how.

•Early hazard identification, reliable risk assessment and diligent risk avoidance strategies are essential.•We describe why toxicology should be an integrated discipline within the drug discovery process.•We focus on target safety assessment, identification of series without inherent safety risks, optimization on safety and profiling of candidates.•We discuss the safety areas to be addressed with screening during the discovery process.