ACE inhibitors work by manipulating the renin-angiotensin system. This system is a self-regulating feedback loop that begins in the kidney with the production of renin in response to a drop in blood pressure. Renin is converted into angiotensin. In turn, angiotensin is converted into angiotensin II through the action of angiotensin converting enzymes. Angiotensin II is a potent vasoconstrictor that causes constriction of the arteries in the body, as well as retention of water and sodium. Thus, lower levels of angiotensin II are desirable because arteries are more relaxed and open.

As their name implies, ACE inhibitors work by inhibiting the action of the angiotensin converting enzymes, thus preventing the conversion of angiotensin to angiotensin II. ACE inhibitors are not the only blood pressure medication that works on the renin-angiotensin system. The closely related angiotensin II receptor blockers, or ARBs, work by preventing angiotensin II from connecting with its receptor, thus negating its effect. Additional drugs are under development that would prevent the production of renin. 

ACE inhibitors are widely used in the treatment of high blood pressure (hypertension), as well as other conditions such as heart failure and after heart attack. They are generally taken in the following forms:

The medication generally begins to affect the body within one to two hours after each oral dose (i.e., tablet, capsule or liquid) and almost instantly after IV injection.

ACE inhibitors include medications such as: