Mechanism of action refers to the biochemical interaction by which a drug produces its pharmacological effect.
In pharmacology, the term mechanism of action refers to the specific biochemical interaction through which a drug substance produces its pharmacological effect. This usually includes mention of the specific molecular targets to which the drug binds, such as an enzyme or receptor. Receptor sites have specific affinities for drugs based on the chemical structure of the drug, as well as the specific action that occurs there.
Some drugs (such as antacids and laxatives) do not bind to receptors to produce their corresponding therapeutic effect but simply interact with chemical or physical properties in the body.
In comparison, a mode of action describes functional or anatomical changes, at the cellular level, resulting from the exposure of a living organism to a substance.
Questions using this tag should relate to the pharmacological mechanism of action of a drug.
Reference: Wikipedia - Mechanism of Action