Pharmacology and Toxicology together form a discipline that examines the interactions of chemical substances with living systems.  Pharmacology focuses on the properties of drugs, including their sites of action, processing by the human body, and therapeutic uses.  Toxicology studies the adverse effects of chemicals such as environmental agents and synthetic compounds, including drugs and their metabolites, and the means to prevent or treat their effects.  Because the study of chemicals requires an intimate knowledge of the biological systems affected, Pharmacology and Toxicology are by necessity an integrative discipline that studies the effects of chemicals at the molecular, cellular, organ, organismal, and population levels.