Calcium-channel blockers

Published by Bupa's Health Information Team, September 2011.

This factsheet is for anyone taking calcium-channel blockers, or who would like information about them.

Calcium-channel blockers work on the muscle cells of the heart and the arteries. These medicines are used to treat chest pain (angina) and high blood pressure. For more information about these conditions, see Related topics.

Why would I take calcium-channel blockers?

Your GP may prescribe calcium-channel blockers if you have:

• angina
• high blood pressure (hypertension)
• disturbance of the normal heart rhythm (arrhythmia)
• Raynaud's phenomenon (pale, cold hands and feet caused by narrowing of the arteries that supply them with blood)

If you get cluster headaches (severe headaches usually affecting the area around one eye or temple), you may be prescribed a particular type of calcium-channel blocker called verapamil to try to prevent them.

If you have angina, your GP will usually only prescribe a calcium-channel blocker if beta-blockers (a different type of heart medicine) haven’t worked well enough alone or if there is a reason why you can't take them.

What are the main types of calcium-channel blocker?

There are three main types of calcium-channel blockers.

• The phenylalkylamines mainly affect the heart, reducing how hard it can work. You may be prescribed these to treat angina, high blood pressure and arrhythmia. These medicines aren’t suitable if you have heart failure or if you are taking beta-blockers, which also stop your heart working so hard. This group includes verapamil.
• The dihydropyridines mainly affect the arteries, causing them to become wider, which lowers blood pressure. This group includes most of the other commonly used calcium-channel blockers, such as amlodipine and nifedipine.
• The benzothiazepines affect both the heart and the arteries. These can be used to treat angina or high blood pressure. This group includes diltiazem.

Individual calcium-channel blockers work in different ways, so one that is taken to treat a certain condition may not be suitable for another.

How do calcium-channel blockers work?

Effect on the heart

Your heartbeat is controlled by special cells that generate electrical impulses, acting like pacemakers to regulate how often your heart beats. These electrical impulses flow from cell to cell within the heart and are converted into chemical signals.

One of these chemical signals is a rising level of calcium inside the muscle cell. This causes the muscle to contract.

Calcium-channel blockers slow down the amount of calcium that can get into heart muscle cells and so reduce how fast and strongly it can contract. This effect can help with the symptoms of angina and irregular heart rhythms, but this can vary depending on the type of medicine you’re prescribed.

Effect on blood vessels

The arteries that carry blood from your heart to the rest of your body have walls that contain a special type of muscle called smooth muscle, which controls the width of the arteries.

As the level of calcium inside muscle cells increases, the muscle contracts and the artery narrows. This raises your blood pressure because your blood is squeezed into a smaller space.

When calcium channels are blocked calcium can’t enter the cells so there is no signal to contract. Instead, the muscle cells in the blood vessels relax, causing the arteries to widen (this is called vasodilation). This helps to lower your blood pressure. Calcium-channel blockers also prevent angina by widening the coronary arteries that supply the heart and allowing more oxygen to reach the heart muscle cells.

How to take calcium-channel blockers

Calcium-channel blockers are only available on prescription. They usually come as tablets or capsules that you take once or twice a day. Long-acting versions, which are sometimes called 'modified release', are also available.

It’s important that you make sure you always have a prescription for the same brand of calcium-channel blocker because different brands aren’t necessarily absorbed by your body in the same way.

Don’t stop taking a calcium-channel blocker suddenly because this may make angina worse. Your GP will tell you how to reduce your calcium-channel blockers gradually if you need to stop taking them.

Always ask your GP for advice and read the patient information leaflet that comes with your medicine.

Special care

Your GP may not prescribe calcium-channel blockers if you’re pregnant or breastfeeding, have recently had a heart attack or certain other conditions, or are taking beta-blockers. Talk to your GP for more advice.

Side-effects of calcium-channel blockers

Side-effects are the unwanted effects of taking a medicine. This section doesn’t include every possible side-effect of calcium-channel blockers. Please read the patient information leaflet that comes with your medicine for more information.

Calcium-channel blockers can cause a drop in your blood pressure. This can make you feel dizzy when you stand up. To help prevent this, make sure you get up slowly when you stand up from lying or sitting down, and stay next to your bed or chair until you're sure that you aren’t feeling dizzy. Don’t drive or do anything else that needs you to be alert until you know how you react to your medicine.

Calcium-channel blockers slow down your heart (especially the medicines verapamil and diltiazem) and can cause headaches, constipation, flushing of your face and fluid retention, especially around your ankles.

Interactions of calcium-channel blockers with other medicines

Some calcium-channel blockers can be affected if you eat grapefruit or drink grapefruit juice so that the medicine is absorbed by your body at a different rate. Check with your GP or pharmacist whether you can still have grapefruit with the type of calcium-channel blocker you have been prescribed.

Also check with your GP or pharmacist before you take any other medicines or herbal remedies at the same time as a calcium-channel blocker.

Names of common calcium-channel blockers

The main types of calcium-channel blockers are shown in the table.

All medicines have a generic name. Many medicines also have one or more brand names. Generic names are written in lower case, whereas brand names start with a capital letter. 

For answers to frequently asked questions on this topic, see Common questions.

For sources and links to further information, see Resources.