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Calcium-channel blockers


Expert reviewer Dr Tim Cripps, Consultant Cardiologist
Next review due October 2022

Calcium-channel blockers are medicines that work on the muscle cells of your heart and your arteries. They’re used to treat a number of different health conditions.

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Uses of calcium-channel blockers

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

  • angina
  • high blood pressure
  • disturbance of the normal heart rhythm (arrhythmia)
  • Raynaud's phenomenon (a disorder that affects your blood vessels, causing them to narrow in response to cold temperatures or emotional stress)
  • cluster headaches (severe headaches usually affecting the area around one eye or temple)

It’s important to be aware that these medicines aren’t suitable for everyone. If you’re pregnant or breastfeeding, some calcium-channel blockers aren’t advised, or may cause problems. So, you should let your doctor know if you’re pregnant, breastfeeding or planning to have a baby. You should also discuss any other medical conditions you have and medicines that you’re taking.

It’s your decision whether to take a medicine or not. Discuss your options with your doctor and ask them about the pros and cons of any medicines they suggest.

How calcium-channel blockers work

Calcium plays a key role in how the muscles in your heart and arteries contract to pump blood round your body. To do this, calcium flows into these cells through special holes, or channels.

Effect on the heart

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. The medicines also act on special conducting cells, so affecting the speed of electrical flow through your heart. These effects can help with the symptoms of angina and irregular heart rhythms.

Effect on blood vessels

Calcium-channel blockers restrict how much calcium can enter the muscle cells in your blood vessels. These then 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 your heart. This allows more oxygen to reach the heart muscle cells.

Types of calcium-channel blockers

There are two main groups of calcium-channel blocker:

  • dihydropyridine calcium-channel blockers (for example amlodipine, felodipine and nifedipine) which make your arteries become wider. Dihydropyridines may be used to treat Raynaud’s phenomenon, angina and high blood pressure.
  • non-dihydropyridines, or ‘rate-limiting’ calcium-channel blockers (for example diltiazem and verapamil). These widen your arteries and affect your heart, reducing how hard it has to work and how fast it beats. Your doctor may prescribe these medicines to treat angina, high blood pressure and arrhythmia.

Your doctor will offer you the calcium-channel blocker that is most suitable for you. This will depend on the medical condition it’s treating, as well as your general health and other medicines you’re taking.

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Taking calcium-channel blockers

Calcium-channel blockers are only available on prescription, usually as tablets. The information that comes with your medicine will tell you how to take it, and how often. Some calcium-channel blockers come in long-acting ('modified release') versions. To read more about what this means, see our FAQ below, ‘What do the letters SR and XL mean in the name of my medicine?’

If you forget to take a tablet, check the patient information leaflet that comes with your medicine. This will explain what you need to do if you miss a dose of your medicine.

Don’t stop taking your calcium-channel blockers unless your doctor tells you to. Stopping calcium-channel blockers suddenly can cause pain and tightness in your chest (angina). If you need to stop taking your medicine, your doctor will tell you how to do this safely.

Always follow the instructions your doctor or pharmacist gives you about when to take your medicines. Read the patient information leaflet that comes with your medicine carefully. If you have any questions about your medicines or how to take them, ask your pharmacist.

If you’ve taken too much medicine, or think you’re reacting badly to it, seek advice from a health professional immediately. This could be from your pharmacist, doctor or the hospital.

Interactions of calcium-channel blockers

Calcium-channel blockers may interact with certain foods and medicines. For instance:

  • grapefruit juice can increase the effects of the medicine which can cause problems
  • alcohol and calcium-channel blockers can both cause a low blood pressure, so together might cause problems

Check the information which comes with your medicine to see if there are any recommendations about foods and drinks to avoid. And if you have any queries, ask your pharmacist.

Calcium-channel blockers may interact with other medicines, including some other heart medicines and certain antibiotics. If you’re taking beta-blockers, you won’t be able to take certain calcium-channel blockers (such as verapamil). Always check with your pharmacist or doctor before you take any other medicines or herbal remedies at the same time as a calcium-channel blocker.

Side-effects of calcium-channel blockers

You may not get any side-effects but, as with all medicines, they’re a possibility. Side-effects vary, according to which calcium-channel blocker you’re taking. The patient information leaflet can tell you exactly which side-effects may happen and how common they are with your particular medicine. Some of the most common side-effects of calcium-channel blockers include:

  • flushing
  • headache
  • swelling in your feet and ankles
  • dizziness
  • rapid or irregular heart beat (palpitations)
  • nausea (feeling sick or being sick) rashes

Some calcium-channel blockers, especially verapamil, may cause constipation. For more information about this, read our FAQ below, ‘Why does my medicine cause constipation?’

Side-effects may settle down on their own, so give your new medicine a chance and wait a few days to see if things get better. If the side-effects continue and you’re feeling unwell, contact your doctor. Don’t stop taking the medicine without discussing it with your GP first.

Frequently asked questions

  • If you’re taking a calcium-channel blocker, your tablet or capsule may have extra letters such as SR, XL, LA or MR in the name. If so, these have been specially designed to release your medicine slowly and steadily over a longer period of time. Doctors often refer to them as ‘modified release’ medicines. You may be offered these forms of your medicine so that you don’t have to take them so often. Depending on the type, this may be only once, or maybe twice a day.

    If you have this type of calcium-channel blocker, it’s important not to chew or crush them up. This would make their slow-release mechanism ineffective.

    Don’t take a different brand of modified release calcium-channel blocker to the one that has been prescribed for you. Brands can differ in how they affect you.

    If you’re not sure what type of calcium-channel blocker you have, or exactly how to take it, read the patient information that comes with your medicine. If you still have queries, your pharmacist can help.

  • Even though you’re taking calcium-channel blockers for angina or high blood pressure, the medicine can affect other parts of your body too. Calcium-channel blockers have an effect on the muscle which forms part of the walls of your bowel. This can stop your bowel working normally and lead to constipation. Constipation is the most commonly reported side-effect of verapamil. But you may also get constipation with other calcium-channel blockers.

    However, a change in bowel habit such as constipation can also be a symptom of serious disease. Don’t just assume it’s due to your medicine, especially if it starts or gets worse after you’ve been on your medicine for a while. Tell your GP about it.


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Related information

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    • Raynaud's phenomenon. PatientPlus. www.patient.info/doctor, last edited April 2016
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    • Personal communication, Dr Tim Cripps, Consultant Cardiologist, April 2019
  • Reviewed by Dr Kristina Routh, Freelance Health Editor, April 2019
    Expert reviewer Dr Tim Cripps, Consultant Cardiologist
    Next review due October 2022



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