A drug may be defined as any artificial, natural, or endogenous (from within the body) molecule that exerts a biochemical or physiological effect on the cell, tissue, organ, or organism, and pharmacology is a branch of medicine, biology, and pharmaceutical sciences concerned with drug or medication action (sometimes the word pharmakon is used as a term to encompass these endogenous and exogenous bioactive species). It is the study of how chemicals interact with living organisms to impact normal or pathological biochemical function. Pharmaceuticals are defined as compounds that have therapeutic effects. Pharmacodynamics and pharmacokinetics are the two primary branches of pharmacology. Pharmacodynamics is the study of a drug's impacts on biological systems, while pharmacokinetics is the study of a drug's effects on biological systems. Pharmacodynamics is concerned with the interactions of chemicals with biological receptors, while pharmacokinetics is concerned with the absorption, distribution, metabolism, and excretion (ADME) of chemicals from biological systems. The terms pharmacology and pharmacy are not interchangeable, and the two are commonly used interchangeably.