This field of study focuses on the scientific studies of drug interaction and poison/biohazard on biological system, in vivo or in vitro, or both. It covers pharmaco/toxico-dynamic, pharmaco/toxico-kinetics, drug/poison actions, body reactions on drug/poison and specific drug-drug/poison interactions, and changes in parameter(s) studied. Studies on the pathway and mechanism of action are also emphasized. Assessment of extract, bioactive compound from natural sources (plant and animal) or synthetic and their potential in drug discovery and physiological function in relation with toxicological problem is also included.