• Aliskiren -- Aliskiren is classified as a renin inhibitor. It is the first medication in its class. Renin is an enzyme produced in the kidneys that acts throughout the body. It works to convert angiotensinogen to angiotensin I. A different enzyme (angiotensin-converting enzyme, or ACE) then converts angiotensin I to angiotensin II, a powerful substance that increases blood pressure by narrowing blood vessels and indirectly stimulating the kidneys to retain salt.

Many blood pressure medications work in various steps in this process (such as ACE inhibitors or angiotensin II receptor blockers, known as ARBs). However, aliskiren is different; it acts at the beginning of the process, preventing renin from converting angiotensinogen to angiotensin I.

• Hydrochlorothiazide -- Hydrochlorothiazide is a diuretic, which is commonly referred to as a "water pill." It works by increasing the amount of salt and water the kidneys remove from the blood. This extra salt and water is then passed out through the urine. By increasing the amount of water removed from the blood, hydrochlorothiazide causes a decrease in blood volume. Because of this effect, hydrochlorothiazide can lower blood pressure and can also help with water retention.