This type of categorisation is from a pharmacological perspective and categorises them by their biological target. Drug classes that share a common molecular mechanism of action modulate the activity of a specific biological target. The definition of a mechanism of action also includes the type of activity at that biological target. For receptors, these activities include agonist, antagonist, inverse agonist, or modulator.  Enzyme target mechanisms include activator or inhibitor. Ion channel modulators include opener or blocker.  The following are specific examples of drug classes whose definition is based on a specific mechanism of action:
* 5-alpha-reductase inhibitor
* ACE inhibitor
* Alpha-adrenergic agonist
* Angiotensin II receptor antagonist
* Beta blocker
* Cholinergic
* Dopaminergic
* GABAergic
* Incretin mimetic
* Nonsteroidal anti-inflammatory drug − cyclooxygenase inhibitor
* Proton-pump inhibitor
* Renin inhibitor
* Selective glucocorticoid receptor modulator
* Serotonergic
* Statin –  HMG-CoA reductase inhibitor