Inhibitors of the renin-angiotensin system (RAS), angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs), are commonly used in the treatment of hypertension. ACE inhibitors inhibit ACE and decrease blood pressure by decreasing conversion of angiotensin I to angiotensin II. ARBs are the second line treatment option if ACE inhibitors are not tolerated. They cause inhibition of AT1 receptors and decrease vasoconstriction. Aliskiren is a direct renin inhibitor if both ACE inhibitors and ARBs are not tolerated.