Pharmacology is the science that deals with the study of drug origin, nature, chemistry, effects, and uses of drugs. It is the study of body reaction to the drug. It is subdivided into two categories as mentioned above, pharmacodynamics and pharmacokinetics. Molecular pharmacology deals with understanding the molecular basis for the actions of drugs and the characteristics of interactions between drug molecules and those of the substrates of drug action in the cell. The methods of molecular pharmacology include precise mathematical, physical, chemical, molecular biological and all biochemical and cell biological techniques to understand how cells respond to hormones or pharmacologic agents, and how chemical structure correlates with biological activity. Clinical Pharmacology is the study of drugs and the interactions of chemical substances with living beings, with a view to understanding the properties and their actions, including the interactions between drug molecules drug receptors and how these interactions induce an effect.