Your GP may prescribe calcium-channel blockers if you have:
- 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); if you get them your doctor may prescribe a particular type of calcium-channel blocker called verapamil to try to prevent them
Calcium plays a key role in how the muscles in your heart and arteries constrict to pump blood through your heart and round your body. It also controls the electrical flow through your heart. Calcium gets into your cells through calcium channels. These are found in the smooth muscle of your heart and arteries. These channels open and close depending on electrical changes on the surface of the smooth muscle cells. The resulting change in the level of calcium triggers events within the cells. Calcium-channel blockers work by restricting the amount of calcium allowed into the muscle cells through these 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 the speed of electrical flow through your heart. This effect can help with the symptoms of angina and irregular heart rhythms.
Effect on blood vessels
Calcium-channel blockers restrict how much calcium can enter your cells. 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 your heart. This allows more oxygen to reach the heart muscle cells.
There are different types of calcium-channel blocker, and they don’t all work the same way. Some aren’t suitable for certain conditions, and their effects vary. Your doctor will know which one is best to prescribe for you. It’s important that you read your patient information leaflet that comes with the medicine and to ask your doctor any questions you have about it.
As an overview, there are three main types of calcium-channel blocker. These are explained below, with some information about what they may be used for. The three types are:
Dihydropyridines include amlodipine, felodipine, lacidipine, lercanidipine, nicardipine, nifedipine, and nimodipine. They mainly affect the cells in your arteries rather than your heart muscle cells. They cause your arteries to become wider, which lowers blood pressure. Dihydropyridines may be used to treat Raynaud’s phenomenon, angina and high blood pressure. Your doctor will explain which medicine they are prescribing for you. Even though they all belong to the same group, different ones treat different conditions.
These are the medicine and brand names of dihydropyridines.
Medicine Brand name amlodipine Exforge (in combination with valsartan), Istin felodipine Cardioplen XL, Felogen XL, Felotens XL, Keloc SR, Neofel X, Parmid XL, Plendil, Triapin (in combination with ramipril), Vascalpha lacidipine Motens lercanidipine Zanidip nicardipine Cardene, Cardene SR nifedipine Adalat, Adalat LA, Adalat Retard, Adipine MR, Adipine XL, Beta-Adalat (in combination with atenolol), Coracten SR, Coracten XL, Fortipine LA 40, Nifedipress MR, Tenif (in combination with atenolol), Tensipine MR, Valni XL nimodipine Nimotop
Phenylalkylamines mainly affect your heart, reducing how hard it has to work. Your doctor may prescribe these to treat angina, high blood pressure and arrhythmia. These medicines aren’t suitable if you have heart failure or if you’re taking beta-blockers. This group includes verapamil.
These are the medicine and brand names of phenylalkylamines.
Medicine Brand name verapamil Cordilox, Securon, Half Securon SR, Securon SR, Univer, Verapress MR, Vertab SR 240
Benzothiazepines affect both your heart and your arteries. You may have these to treat angina or high blood pressure. This group includes diltiazem and might be used if beta-blockers aren’t suitable for you or if they haven’t worked.
These are the medicine and brand names of benzothiazepines.
Medicine Brand name diltiazem Adizem-SR, Adizem-XL, Angitil SR, Angitil XL, Dilcardia SR, Dilzem SR, Dilzem XL, Slozem, Tildiem, Tildiem LA, Tildiem Retard, Viazem XL, Zemtard
Calcium-channel blockers are only available on prescription. They usually come as tablets or capsules that you take once, twice or sometimes three times a day, depending on the brand you’re taking. Take them with a glass of water, and don’t crush up the tablet or capsule.
Long-acting versions, which are sometimes called 'modified release', are also available. To read more about what this means, see our FAQ: XL and SR calcium-channel blockers.
It’s important that you always have a prescription for the same brand of calcium-channel blocker. This is 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.
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.
Depending on the particular medicine you’re taking, you may need to:
- take your medicine as soon as you remember
- miss the dose out if it is nearly time for your next dose, then take the next one at the usual time
Never take a double dose to make up for one that you have forgotten. It can be potentially harmful to have a high level of the medicine in your body.
Don’t 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).
If you accidentally take too much of your medicine, go to your nearest hospital or contact your GP as soon as possible. Taking too much can cause side-effects such as very low blood pressure which can make you feel weak, faint and light-headed. If your blood pressure gets very low, you can go into shock. This is why it’s really important that you get medical advice if you take too much.
Always ask your GP for advice and read the patient information leaflet that comes with your medicine.
Whenever you start taking a new medicine, or your doctor changes the dose or the type of medicine you’re taking, it’s likely they will ask you to come back for a check up. With calcium-channel blockers, it very much depends on the condition that’s being treated. For high blood pressure, for example, your doctor will likely recommend that you come back after four weeks so they can measure your blood pressure.
If you’re taking other medicines at the same time, your doctor might want to see you more often to check there aren’t any interactions or complications.
Not everyone can take calcium-channel blockers. It depends on the particular type of calcium-channel blocker and the reason you’re taking it. For example, Your GP may not prescribe verapimil or diltiazem if you have:
- heart failure
- recently had a heart attack
- low blood pressure
- a condition called brachycardia (slow heart rate)
It might seem odd that certain heart medicines aren’t advised if you have heart failure. But this is because these types of calcium-channel blocker act on your heart and may prevent your heart from functioning as it needs to. As a result, this can make your condition worse.
If you have a particular existing health condition, you’ll need to discuss whether or not you can take calcium-channel blockers with your doctor or pharmacist. You still may be able to have them, but your doctor may want to monitor you closely.
This includes if you have:
Other calcium-channel blockers, such as amlodipine and verapamil, also aren’t advised if you’re pregnant. However you may need to keep taking them for your own health. Your GP will weigh up the risk of harm to your baby with your need for the medicine. Talk to your GP for more advice about this.
Calcium-channel blockers may interact with certain foods and medicines.
Some calcium-channel blockers, such as verapamil, can be affected if you eat grapefruit or drink grapefruit juice. This can increase the effects of the medicine which can cause problems. Check with your pharmacist to see if you can still have grapefruit with your calcium-channel blocker.
Alcohol can have a similar effect to grapefruit juice so it’s best not to drink alcohol when you’re taking calcium-channel blockers. Check your patient information leaflet for specific advice about your calcium-channel blocker and alcohol.
Calcium-channel blockers can also 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 calcium-channel blockers. Always check with your GP or pharmacist before you take any other medicines or herbal remedies at the same time as a calcium-channel blocker.
You might not get any side-effects but, as with all medicines, they are a possibility. Even if you do get some side-effects, they will often be mild and ease a few days after you start taking the medicine. Because calcium-channel blockers have different effects, it’s not possible to say here how common or rare some of these side-effects are – it depends on which calcium-channel blocker you’re taking. Your patient information leaflet can tell you exactly which side-effects may happen and how common they are with your particular medicine. Some side-effects include:
- tummy (abdominal) pain
- rapid or irregular heart beat (palpitations)
- nausea (feeling sick or being sick)
- swelling in your feet and ankles
- low blood pressure (hypotension)
Verapamil can commonly cause constipation. For more information about this, read our FAQ: Calcium-channel blockers and constipation
Give your new medicine a chance and wait a few days to see if any side-effects ease. If they continue and you’re feeling unwell, contact your doctor. Don’t stop taking the medicine without your GP’s advice. It can be dangerous to suddenly stop taking calcium-channel blockers because that may cause angina to become worse.
SR means sustained release and XL means extended or prolonged 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 to be broken down slowly in your body. This means that the medicine takes longer to get into your bloodstream. This gives you a steady, continuous dose of the medicine, so its effects last for longer than an ordinary tablet. Different forms may release the active medicine into your bloodstream at different rates.
The SR forms of calcium-channel blockers have 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), LA (long acting) or Retard, but these all mean the same as SR.
The XL forms of calcium-channel blockers are 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.
Diltiazem and nifedipine are examples of calcium-channel blockers that have a number of different extended (slow)-release forms.
You must swallow these formulations whole and not chew or crush them up, as this makes their extended (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. Different brands can be released into your body at slightly different rates.
Constipation is the most commonly reported side-effect of verapamil. But you may also get constipation with other calcium-channel blockers.
Constipation is likely to be caused by the medicine disrupting the normal way your bowel works. This is because you have smooth muscle in your gastrointestinal (GI) tract as well as in your heart and arteries. Your gastrointestinal tract includes your oesophagus, stomach, small and large intestine, back passage (rectum) and anus. If the medicine acts on the calcium-channels in your GI tract, this can stop your bowel working normally and lead to constipation.
So, even though you’re taking calcium-channel blockers for your heart, the medicine can affect other parts of your body too. This means your bodily functions, including how your digestive system processes food, are also affected. Lots of people find side-effects like this settle down or aren’t too disruptive, but if you’re worried about constipation or it’s affecting you, it’s always worth talking to your GP about it.
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