Pharmacology is the science concerned with all aspects of the action of drugs and other chemicals on living systems. Its primary aim is the discovery of chemical mechanisms by which cellular and molecular functions are regulated for the purpose of understanding how existing drugs act and to develop new drugs for treatment and diagnosis of human diseases. The discipline of pharmacology explores biology through the actions of drugs and chemical substances. Drugs and chemicals produce their effects only through modifications of underlying biological systems; their actions are useful in regulating not only normal functions of cells and organisms but also the abnormal processes which occur in disease.