Enalapril is a prodrug because it is an inactive compound that is converted into its active form, enalaprilat, in the body. Enalaprilat is the active form that inhibits the enzyme responsible for the production of angiotensin II, a potent vasoconstrictor. By inhibiting this enzyme, enalaprilat helps to relax and widen the blood vessels, reducing blood pressure. The conversion of enalapril to enalaprilat occurs in the liver, making it a prodrug.