1. About diltiazem

Diltiazem is a medicine used to treat high blood pressure.

If you have high blood pressure, taking diltiazem helps to prevent future heart disease, heart attacks and strokes.

Diltiazem is also used to prevent chest pain caused by angina as well as Raynaud's phenomenon. It can also be used to help heal an anal fissure.

It's available on prescription only and comes as tablets, capsules, cream or ointment.

2. Key facts

  • Diltiazem works by lowering your blood pressure and makes it easier for your heart to pump blood around your body.
  • You can take diltiazem at any time of day. Try to make sure it's around the same time or times every day.
  • Common side effects include swollen hands, ankles or feet, headaches and constipation.
  • Diltiazem starts to work on the day you start taking it, but for high blood pressure and angina it may take a couple of weeks to work fully.
  • It's important to keep taking diltiazem even if you feel well, as you'll still be getting the benefits of the medicine.

3. Who can and cannot take diltiazem

Diltiazem can be taken by adults and children aged 12 years and over.

Diltiazem is not suitable for some people.

To make sure diltiazem is safe for you, tell your doctor if you:

  • have had an allergic reaction to diltiazem or any other medicines in the past
  • are trying to get pregnant, are already pregnant or you're breastfeeding
  • have liver disease or kidney disease
  • have heart failure or problems with your heart beat
  • have a condition that causes food to move slower than usual through your body
  • have porphyria (a blood disorder)

4. How and when to take it

Take diltiazem exactly as your doctor has told you. If you're not sure, check with your doctor or pharmacist.

You can take diltiazem at any time of day but try to make sure it's around the same time or times every day.


Your dose of diltiazem depends on why you need the medicine and what kind your doctor has prescribed. It is important to keep taking the same brand of diltiazem once you have started.

Diltiazem tablets or capsules come as standard (immediate release) or slow-release (prolonged release, SR or XL). Your doctor will tell you whether you need to take them once a day or in divided doses throughout the day.

Slow-release tablets release diltiazem slower than the immediate-release tablets.

How to take or apply it

You can take diltiazem with or without food. Swallow diltiazem tablets or capsules whole, usually with a glass of water. Do not chew or crush them.

If you find tablets or capsules difficult to swallow, speak to a pharmacist or doctor, as there may be other options.

With some of the capsules and tablets you might notice what looks like a whole capsule or tablet in your poo. Do not worry, this is normal. It's just the empty outer shell of the capsule or tablet which your body has not digested.

For anal fissure, you'll need to apply a 2cm length of diltiazem cream or ointment to the broken skin on your anus, twice a day, usually for 6 weeks. Follow the instructions on the packaging.


Keep taking diltiazem even if you feel well, as you'll still be getting the benefits of the medicine.

Will my dose go up or down?

If the dose you start on does not work well enough (your blood pressure does not lower enough, or your angina is not controlled), then your doctor will gradually increase your dose.

Your doctor may also lower your dose if the side effects bother you.

What if I forget to take it?

If you forget to take a dose and you usually take diltiazem:

  • once a day take it as soon as you remember, unless it's less than 12 hours until your next dose. In this case, leave out the missed dose and take your next dose at the usual time.
  • twice a day take it as soon as you remember, unless it's less than 4 hours until your next dose. In this case, leave out the missed dose and take your next dose at the usual time.
  • three times a day leave out that dose and take your next dose at the usual time.

Do not take a double dose to make up for a forgotten one.

If you forget doses often, it may help to set an alarm to remind you. You could also ask a pharmacist for advice on other ways to help you remember to take your medicine.

What if I take too much?

Urgent advice: Contact 111 for advice if:

  • you take too much diltiazem

Too much diltiazem can make you feel faint, dizzy or sleepy. This is because it can cause your heart to beat irregularly.

If you need to go to hospital, do not drive yourself; get someone else to drive you or call for an ambulance. Find your nearest A&E

Take the diltiazem packet or leaflet inside it, plus any remaining medicine, with you.

5. Side effects

Like all medicines, diltiazem can cause side effects, although not everyone gets them.

Common side effects

These common side effects happen in more than 1 in 100 people. They are usually mild and will not last long.

Talk to a pharmacist or doctor if the side effects bother you or last for more than a few days:

  • swollen hands, ankles or feet
  • headaches
  • feeling dizzy and lightheaded
  • feeling tired, weak and generally unwell
  • feeling hot (flushing) and redness of the skin
  • itching or burning on the skin where you use the cream or ointment
  • stomach pain, indigestion and constipation

Serious side effects

Serious side effects after taking diltiazem are rare and happen in less than 1 in 10,000 people.

Stop taking diltiazem and call a doctor straight away if you get:

  • severe pain in your stomach
  • yellow skin or the whites of your eyes turn yellow – this can be a sign of liver problems

Immediate action required: Call 999 or go to A&E now if:

  • you have chest pain that's new or gets worse – this needs to be checked by a doctor as chest pain is a possible sign of a heart attack.

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to diltiazem.

Immediate action required: Call 999 or go to A&E now if:

  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
  • you're wheezing
  • you get tightness in the chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling

You could be having a serious allergic reaction and may need immediate treatment in hospital.

These are not all the side effects of diltiazem. For a full list, see the leaflet inside your medicine packet.

You can report any suspected side effects to the UK safety scheme.

6. How to cope with side effects

What to do about:

  • swollen hands, ankles or feet raise your legs when you're sitting down. This will get better after a few days as your body gets used to the medicine. If it does not, or it gets worse, speak to your doctor.
  • headaches make sure you rest and drink plenty of fluids. Do not drink too much alcohol. Ask a pharmacist to recommend a painkiller. Paracetamol is safe to take with diltiazem. Headaches should usually go away after the first week of taking diltiazem. Talk to your doctor if they last longer than a week or are severe.
  • feeling dizzy and lightheaded if diltiazem makes you feel dizzy, stop what you're doing and sit or lie down until you feel better. Do not drive, ride a bike or operate tools or machinery until you feel OK.
  • feeling tired and weak make sure you rest and drink plenty of fluids. Do not drink too much alcohol. Try to take diltiazem at a time when you can sit down (or lie down) when the symptoms are at their worst. If you're still having problems after a week, speak to your doctor, as they may need to change you to a different type of medicine. Do not drive or use tools or machinery until you feel OK.
  • feeling hot (flushing) and redness of the skin try cutting down on coffee, tea and alcohol. It might help to keep the room cool and use a fan. You could also spray your face with cool water or sip cold or iced drinks. The flushing should go away after a few days. If it does not go away or it's causing you problems, contact your doctor.
  • itching or burning on the skin try holding something cool on your skin like a damp towel. Take cool baths or showers. If you have itchy skin, use an unperfumed moisturiser regularly. However, do not use moisturiser on an anal fissure as this will irritate it more. Keep your nails clean, short and smooth and try to pat or tap your skin rather than scratching.
  • stomach pain try to rest and relax. It can help to eat and drink slowly and have smaller and more frequent meals. Putting a heat pad or covered hot water bottle on your stomach may also help. If you are in a lot of pain, speak to a doctor or pharmacist. 
  • indigestion – it might help to eat smaller and more frequent meals, and to eat and drink slowly. Talk to your doctor if the symptoms get worse.
  • constipation eat more high-fibre foods such as fresh fruit, vegetables and cereals, and drink plenty of water. Try to exercise regularly, for example, by going for a daily walk or run. If this does not help, talk to a pharmacist or doctor. Watch this short video about how to treat constipation.

7. Pregnancy and breastfeeding

Diltiazem is not usually recommended in pregnancy.

If you're trying to get pregnant, or you're already pregnant, talk to your doctor about the benefits and possible harms of taking diltiazem. There may be other medicines that are safer for you.

Find out more about how diltiazem and other calcium channel blockers can affect you and your baby during pregnancy on the Best Use of Medicines in Pregnancy (BUMPS) website.

Diltiazem and breastfeeding

If your doctor or health visitor says your baby is healthy, diltiazem can be used during breastfeeding.

Diltiazem passes into breast milk in small amounts, with very few babies getting side effects.

It's important to keep taking diltiazem to keep you well. Breastfeeding will also benefit both you and your baby.

If you notice that your baby is not feeding as well as usual, seems unusually sleepy, or if you have any other concerns about your baby, talk to your health visitor or doctor straight away.

8. Cautions with other medicines

Some medicines can interfere with the way diltiazem works.

Taking diltiazem with other medicines that lower blood pressure can sometimes lower your blood pressure too much. This may make you feel dizzy or faint. If this happens to you, tell your doctor, as your dose may need to be changed.

Tell your doctor if you are taking any of these medicines before starting diltiazem:

Taking diltiazem with painkillers

Paracetamol is the best painkiller to take while you're taking diltiazem. If paracetamol does not work, try ibuprofen.

Talk to your doctor if you need to take painkillers more than a few times a week.

Mixing diltiazem with herbal remedies or supplements

St John's wort is a herbal medicine taken for depression. It is thought to interfere with the way diltiazem works.

Talk to a pharmacist or doctor if you're thinking about taking St John's wort.


Tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.

9. Common questions

Page last reviewed: 30/01/2020
Next review due: 30/01/2023