Calcium-channel blockers

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

This section contains answers to common questions about this topic. Questions have been suggested by health professionals, website feedback and requests via email.

What is the difference between XL and SR forms of a medicine?


XL means extended release and SR means sustained release. XL forms of calcium-channel blockers last for longer in your body than SR forms. This means you need to take them less often.


Some types of tablets or capsules are designed specifically to be broken down slowly in your body, so that the medicine takes longer to get into your bloodstream. This means your body receives a steady, continuous dose of the medicine, and its effects last for longer than those of an ordinary tablet. Different forms may release the active medicine into your bloodstream at different rates.

The SR form of calcium-channel blockers has been modified to release the medicine over a few hours, for example, the medicine might be in granule form rather than powder form. You will usually take them twice daily. Different brands of medicine may use the terms MR (modified release), CR (controlled release) or Retard, but these all mean the same as SR.

The XL form of calcium-channel blockers is designed to stay in your body even longer – usually more than 24 hours. This means you may only have to take your medicine once a day. Different brands of medicine may use the term LA (long-acting) instead of XL.

Diltiazem and nifedipine are examples of calcium-channel blockers that have a number of different slow-release forms.

You must swallow these types of medicine whole and not chew, crush or break them up, as this makes their slow-release mechanism ineffective. It can be dangerous if all the medicine is released into your body at once.

Don’t take a different brand of calcium-channel blocker to the one that has been prescribed for you, as different brands can be released into your body at slightly varying rates.

I have forgotten to take a tablet – what can I do?


This depends on the exact type of calcium-channel blocker you’re taking, and how late you are with taking your medicine.


First, check the patient information leaflet that comes with your medicine to find out what you need to do if you miss a dose of your medicine. Usually, you will just need to take your medicine as soon as you remember. But, if it's nearly time for your next dose, you should miss a dose and just take the next one at the usual time. Never take a double dose to make up for one that you have forgotten because it can be dangerous to have a high level of the medicine in your body.

With some medicines, you must not take the missed tablet/capsule if you are more than four hours late taking the dose. All medicines are different, so it's important that you check the patient information leaflet. If you’re still unsure, speak to your pharmacist or GP.

Never stop taking your calcium-channel blockers unless your GP tells you to. Calcium-channel blockers need to be stopped gradually because stopping them suddenly can cause pain and tightness in your chest (angina). 

Can I carry on taking my calcium-channel blocker if I become pregnant?


You may need to stop taking your calcium-channel blocker if you become pregnant. However, talk to your GP before stopping any medicines – he or she will tell you if you need to change your medicine.


Some calcium-channel blockers aren’t advised for women who are pregnant. Tell your GP if you’re trying for a baby or have become pregnant.

In particular, diltiazem can be harmful to your unborn baby. It shouldn't be taken during pregnancy or if you're trying for a baby. Your GP might prescribe a different medicine instead. Other calcium-channel blockers, such as nifedipine and verapamil, are also thought to be best avoided while pregnant, but you may need to keep taking them for your own health. If you’re taking these medicines, your GP will weigh up the risk of harm to your baby against your need for the medicine.

If you usually take calcium-channel blockers for high blood pressure and want to try for a baby or you become pregnant, your GP may suggest you switch to a different type of medicine, such as a beta-blocker or a medicine called methyldopa.

You may also need to carry on taking alternative medicines to calcium-channel blockers while you’re breastfeeding, as the medicines can get into your breast milk.


For our main content on this topic, see Information.

For sources and links to further information, see Resources.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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  • Publication date: September 2011

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