Q.Why do we need to classify drugs in different ways ?

No single classification scheme captures every useful aspect of a drug, so drugs are classified in four complementary ways:

• On the basis of pharmacological effect — groups drugs by what effect they produce (e.g. "analgesics", "antacids"). This is the most useful classification for a doctor, who needs to quickly choose a drug appropriate for a patient's symptoms.
• On the basis of drug action — groups drugs by their biochemical mechanism at the molecular level (e.g. all drugs that block a particular receptor), independent of chemical structure. This helps understand how a drug works.
• On the basis of chemical structure — groups drugs sharing a common structural skeleton or functional groups, since structurally similar drugs often show similar biological activity (structure–activity relationship). This is useful when synthesising new variants.
• On the basis of molecular targets — groups drugs by the specific biomolecule (enzyme or receptor) they act on. This is the most useful classification for medicinal chemists, because it directly indicates the chemical/structural requirements a molecule must have to interact with that particular target, guiding rational design of new drugs.

Since clinical use, mechanistic understanding, and drug design each need a different lens, all four classifications are needed together.

List the four classification schemes (effect, action, structure, target). For each, state who it is useful for and why. Conclude that multiple schemes are needed because no single one serves both clinical and drug-design purposes.

• Naming only one classification scheme instead of explaining why several coexist.
• Confusing classification by chemical structure with classification by molecular target — the former is about the drug's own skeleton, the latter about what it binds to.