Angiotensin II Receptor Blockers (ARBs) and Angiotensin-Converting Enzyme (ACE) inhibitors differ the most in the way that they affect the renin-angiotensin-aldosterone (RAA) system, which helps to control blood pressure. Other slight differences between ARBs and ACE inhibitors can include a decreased risk of certain side effects, especially persistent cough, with ARBs. Some studies have suggested that women who use ARBs after a heart attack have higher survival rates than women who use ACE inhibitors. In most other ways, these two classes of drugs are very similar.

ARBs and ACE inhibitors affect the RAA system in slightly different ways that both relate to angiotensin II. This is a powerful chemical that signals blood vessels to constrict, and it can contribute to hypertension. ARBs, such as candesartan, losartan and irbesartan, prevent angiotensin II from connecting with receptors on small arteries. This means blood vessels don’t narrow and blood pressure is reduced.

The action of ACE inhibitors is very different, though the overall effect is similar. Medications like benzapril, enalapril, and lisinopril prevent the conversion of angiotensin I into angiotensin II. The absence of this chemical means the blood vessels get few chemical messages to constrict, and blood pressure normalizes.

Another difference between ARBs and ACE inhibitors may be the degree to which certain side effects are experienced. Patients who have trouble tolerating ACE inhibitors are often switched to an ARB. This is mainly due to the symptoms of difficult coughing that ACE inhibitors commonly cause. An ARB can have this side effect, too, but not as often, and many patients are made more comfortable if they switch to one.

Moreover, preliminary research suggests that ARBs may be a better choice for women who have experienced a heart attack. Some studies have evaluated mortality rates in women who take ARBs and ACE inhibitors after a heart attack. The evidence suggests that ARBs appear to improve life expectancy, but only for women. There needs to be more study in this area to confirm these results.

Despite some differences, ARBs and ACE inhibitors are similar in a vast number of ways. They’re both recommended to regulate high blood pressure, lengthen survival after a heart attack, and slow the progression of kidney failure as caused by diabetes. Drugs from these classes may additionally protect against stroke. It's also suggested that these medications may help prevent high cholesterol.

ARBs and ACE inhibitors also have comparable side effects. Common ones are headache, dizziness and cough. Additional adverse reactions include diarrhea, rash, and allergy. Both classes of drugs can cause serious birth defects and may interact with the same medications, like lithium.