Here is a list of the different classes of medications, and how that class of medications work, from the National Heart Lung and Blood Institute. There are usually several different specific medications within each class.
(We are pretty lucky now. When I was in medical school the number of medications was very limited, and the incidence of side effects therefore considerably higher.)
Today's blood pressure medicines can safely help most people control their blood pressure. These medicines are easy to take. The side effects, if any, tend to be minor.
If you have side effects from your medicines, talk with your doctor. He or she might adjust the doses or prescribe other medicines. You shouldn't decide on your own to stop taking your medicines.
Blood pressure medicines work in different ways to lower blood pressure. Some remove extra fluid and salt from the body to lower blood pressure. Others slow down the heartbeat or relax and widen blood vessels. Often, two or more medicines work better than one.
Diuretics sometimes are called water pills. They help your kidneys flush excess water and salt from your body. This reduces the amount of fluid in your blood, and your blood pressure goes down.
Diuretics often are used with other HBP medicines and sometimes combined into one pill.
Beta blockers help your heart beat slower and with less force. As a result, your heart pumps less blood through your blood vessels. This causes your blood pressure to go down.
ACE inhibitors keep your body from making a hormone called angiotensin II. This hormone normally causes blood vessels to narrow. ACE inhibitors prevent this, so your blood pressure goes down.
Angiotensin II Receptor Blockers
Angiotensin II receptor blockers are newer blood pressure medicines that protect your blood vessels from the angiotensin II hormone. As a result, blood vessels relax and widen, and your blood pressure goes down.
Calcium Channel Blockers
Calcium channel blockers keep calcium from entering the muscle cells of your heart and blood vessels. This allows blood vessels to relax, and your blood pressure goes down.
Alpha blockers reduce nerve impulses that tighten blood vessels. This allows blood to flow more freely, causing blood pressure to go down.
Alpha-beta blockers reduce nerve impulses the same way alpha blockers do. However, they also slow the heartbeat like beta blockers. As a result, blood pressure goes down.
Nervous System Inhibitors
Nervous system inhibitors increase nerve impulses from the brain to relax and widen blood vessels. This causes blood pressure to go down.
Vasodilators relax the muscles in blood vessel walls. This causes blood pressure to go down."