Enalapril is an angiotensin-converting enzyme (ACE) inhibitor primarily used to treat hypertension. It works by inhibiting the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor, thereby causing vasodilation and reducing blood pressure. This mechanism also decreases aldosterone secretion, leading to reduced sodium and water retention, further lowering blood pressure. Enalapril is effective in preventing complications of hypertension such as heart failure and kidney damage. It is not indicated for asthma, hyperthyroidism, or peptic ulcer treatment.

Reference: Goodman & Gilman's The Pharmacological Basis of Therapeutics, Brunton, 13th Edition.