Pharmacology deals with the elucidation of molecular and organismal function in relation to chemicals .
Pharmacology is the branch of biology concerned with the study of drug action , where a drug can be broadly defined as any man-made , natural , or endogenous ( from within the body ) atoms which exerts a biochemical or physiological effect on the cell , tissue , organ , or organism ( sometimes the word pharmacon is used as a term to encompass these endogenous and exogenous bioactive species ) .