Calcium channel blockers are medicines used to lower blood pressure. They stop calcium from entering the cells of the heart and arteries. Calcium causes the heart and arteries to squeeze more strongly. By blocking calcium, calcium channel blockers allow blood vessels to relax and open.

Some calcium channel blockers also can slow the heart rate. This can further lower blood pressure. The medicines also may be prescribed to relieve chest pain, called angina, and control an irregular heartbeat.

Calcium channel blockers are sometimes called calcium antagonists.

Calcium channel blockers are available in short-acting and long-acting forms. Short-acting medicines work quickly, but their effects last only a few hours. Long-acting medicines are slowly released to provide a longer-lasting effect. Which one is best for you depends on your health and the condition being treated.

Examples of calcium channel blockers include:

• Amlodipine (Norvasc).
• Diltiazem (Cardizem, Tiazac, others).
• Felodipine.
• Isradipine.
• Nicardipine.
• Nifedipine (Procardia).
• Nisoldipine (Sular).
• Verapamil (Verelan).

Sometimes, a calcium channel blocker may be prescribed with other high blood pressure medicines.

In addition to being used to treat high blood pressure, calcium channel blockers may be prescribed to prevent, treat or improve symptoms of conditions, such as:

• Coronary artery disease.
• Chest pain, called angina.
• Irregular heartbeats, also called arrhythmia.
• Blood vessel conditions, such as Raynaud's disease.

For Black people, calcium channel blockers might work better than other blood pressure medicines, such as beta blockers, angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers.

Side effects of calcium channel blockers may include:

• Constipation.
• Dizziness.
• Fast heartbeat you can feel.
• Extreme tiredness.
• Flushing.
• Headache.
• Nausea.
• Swelling in the feet and lower legs.

Avoid grapefruit products while taking the calcium channel blockers diltiazem and verapamil. Grapefruit juice interacts with these medicines and can affect heart rate and blood pressure. This can cause symptoms such as headaches and dizziness.

Talk to your health care team if you have any questions about the medicines you take.