Calcium-channel Blockers

Authored by , Reviewed by Dr Colin Tidy | Last edited | Meets Patient’s editorial guidelines

Calcium-channel blockers (sometimes called calcium antagonists) are a group of medicines that affect the way calcium passes into certain muscle cells. They are used to treat various conditions, including high blood pressure, angina, Raynaud's phenomenon and some abnormal heart rhythms (arrhythmias). They are also used to try to stop premature labour in pregnancy.

A calcium-channel blocker can be used alone. However, one is often combined with another medicine to treat high blood pressure or angina, when one medicine alone has not worked so well.

The heart is mainly made of special muscle cells which contract to pump blood into the blood vessels (arteries). The walls of the arteries also contain 'smooth' muscle cells. When these contract, the artery narrows. The heart muscle cells and smooth muscle cells need calcium to contract. Calcium passes into these cells via tiny 'channels'.

Calcium-channel blockers reduce the amount of calcium that goes into these muscle cells. This causes these muscle cells to relax. So, the effects of these medicines are:

  • To widen the arteries, which:
    • Reduces the blood pressure.
    • Helps to ease angina by widening the coronary arteries.
    • Can ease symptoms of Raynaud's phenomenon. In this condition you have cold and painful fingers and toes, caused by narrowing of the arteries in the hands and feet.
  • To reduce the force and rate of the heartbeat. This helps to prevent angina pains.

When a pregnant woman goes into labour too early, calcium-channel blockers stop the muscles of the womb (uterus) from contracting.

Different types of calcium-channel blockers differ in the main sites of action in the body:

As they have very little effect on the special conducting cells in the heart, dihydropyridine calcium-channel blockers are not useful for arrhythmias. They are also unlikely to make heart failure worse. They are safe to take with a beta-blocker.

  • Angina and high blood pressure are commonly treated with verapamil. You should not take verapamil in addition to a beta-blocker medicine.
  • Angina and high blood pressure are treated with diltiazem.

As a rule, you should not take verapamil or diltiazem if you have heart failure. This is because they 'relax' the heart and can make heart failure worse.

Most people who take calcium-channel blockers have no side-effects, or only minor ones. Because their action is to relax and widen blood vessels (arteries), some people develop flushing and headache. These tend to ease over a few days if you continue to take the tablets. Mild ankle swelling is also quite common, particularly with dihydropyridine calcium-channel blockers.

Constipation is quite a common side-effect, especially with verapamil. You can often deal with this by increasing the amount of fibre that you eat and increasing the amount of water and other fluids that you drink.

Other side-effects are uncommon and include feeling sick, palpitations, tiredness, dizziness and rashes. This is not a complete list of all possible known side-effects. Read the information leaflet that comes with your particular brand for a full list of possible side-effects. However, be optimistic - don't necessarily be put off taking these tablets. Serious side-effects are rare and it's wise not to stop calcium-channel blockers without speaking with your doctor.

How to use the Yellow Card Scheme

If you think you have had a side-effect to one of your medicines you can report this on the Yellow Card Scheme. You can do this online at

The Yellow Card Scheme is used to make pharmacists, doctors and nurses aware of any new side-effects that medicines or any other healthcare products may have caused. If you wish to report a side-effect, you will need to provide basic information about:

  • The side-effect.
  • The name of the medicine which you think caused it.
  • The person who had the side-effect.
  • Your contact details as the reporter of the side-effect.

It is helpful if you have your medication - and/or the leaflet that came with it - with you while you fill out the report.

Further reading and references