**3.3 Molecular effects**

Drug by interacting with the macromolecules of the cellular organelles like, proteins, lipids, etc. causes some changes in the rate or magnitude of an intrinsic cellular response without producing any new responses. Many drugs that have been interacting with receptors (e.g., serum albumin) within the body do not cause any biochemical or physiological response directly even though some positive and negative effects like agonism and antagonism are stimulated by the action of the drug to the receptor. The understanding of drug interactions at the molecular level guides us to know about drug's effect in detail, and hence the dosage and distribution of the drug.
