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Medicine guide

Diltiazem

About this information

This NHS content is written for people in England. Medicine names, availability, prescribing and services may differ in other countries.

Diltiazem is a medicine used to treat high blood pressure.

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

It works by lowering your blood pressure and making it easier for your heart to pump blood around your body.

Diltiazem is also used to:

Diltiazem is available on prescription only. It comes as tablets or capsules to treat high blood pressure, angina or Raynaud's. It's also available as a cream or ointment to treat anal fissures.

Who can take diltiazem

Most adults and children aged 12 years old and over can take diltiazem.

Who may not be able to take diltiazem

Diltiazem is not suitable for some people.

To make sure it's safe for you, tell your doctor if you:

  • have ever had an allergic reaction to diltiazem or any other medicine
  • are pregnant, trying to get pregnant or breastfeeding
  • have liver disease or kidney disease
  • have heart failure or problems with your heartbeat
  • have a condition that causes food to move slower than usual through your body
  • have a rare inherited condition called porphyria

Dosage

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

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

Slow-release tablets and capsules release diltiazem slower than the standard tablets and capsules.

Changes to your dose

If the dose you start on does not reduce your blood pressure enough or help to control your angina, then your doctor will gradually increase your dose.

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

How to take tablets or capsules

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.

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

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 does not digest.

How to use cream or ointment

For an anal fissure, you'll need to apply a 2.5cm length of diltiazem cream or ointment to the broken skin on your anus, twice a day, usually for 6 to 8 weeks. Follow the instructions on the packaging.

How long to take it for

If you're taking diltiazem for high blood pressure or angina, you'll usually take it long term, even for the rest of your life.

Talk to your doctor if you want to stop taking diltiazem. Stopping may cause your blood pressure to rise and this may increase your risk of a heart attack or stroke.

If you're using it to treat an anal fissure, you'll use the cream or ointment to heal the tear on your anus until it's no longer painful to poo. This will mean the tear has healed. This usually takes around 6 to 8 weeks.

If you stop using the cream before a fissure has fully healed, it may tear again.

If you're bothered by side effects, your doctor may be able to prescribe you a different medicine.

Important

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

If you 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, skip 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, skip the missed dose and take your next dose at the usual time
  • 3 times a day – skip the missed dose and take your next dose at the usual time

Never have an extra 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.

If you take too much

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

Contact 111 for advice if:

  • you take more than your prescribed dose of diltiazem

Go to 111.nhs.uk or call 111

Information

If you need to go to A&E, do not drive. Ask someone to drive you or call 999 and ask for an ambulance.

Bring the diltiazem packet or leaflet inside it, any remaining medicine, and any other medicines you take.

Common side effects

These common side effects of diltiazem happen in more than 1 in 100 people. They are usually mild and will not last long. There are things you can do to help cope with them:

Swollen hands, ankles or feet

Raise your legs or the swollen area on a chair or pillows when you can.

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 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 light-headed

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. Do not drink alcohol as it will make you feel worse.

Feeling tired, weak and generally unwell

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, cycle 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 where you use the cream or ointment

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're 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

Get more fibre into your diet 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.

Speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or does not go away.

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 or call 111 now if:

  • you get severe pain in your stomach
  • the whites of your eyes turn yellow, or your skin turns yellow although this may be less obvious on brown or black skin – this can be a sign of liver problems
  • your heartbeat becomes noticeable (palpitations)

Call 999 or go to A&E now if:

  • you get chest pain that does not stop after a few minutes or is new or worse if you already have angina

Chest pain is a possible sign of a heart attack and needs to be checked out as soon as possible.

Meds - serious side effects A&E safety messaging

Do not drive to A&E. Ask someone to drive you or call 999 and ask for an ambulance.

Bring all the medicines you take with you.

Serious allergic reaction

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

Meds New IA (H4) - serious allergic reaction

Call 999 now if:

  • your lips, mouth, throat or tongue suddenly become swollen
  • you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
  • your throat feels tight or you're struggling to swallow
  • your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
  • you suddenly become very confused, drowsy or dizzy
  • someone faints and cannot be woken up
  • a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)

You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.

These can be signs of a serious allergic reaction and may need immediate treatment in hospital.

Other side effects

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

Diltiazem and pregnancy

You can use diltiazem during pregnancy, although it's not usually recommended.

If you're taking diltiazem to treat high blood pressure, you might be switched to a different medicine if you're pregnant.

If you're taking diltiazem for angina or heart rhythm problems, you should be reviewed by a pregnancy specialist (obstetrician) and a heart specialist (cardiologist). Keep taking diltiazem until you've had your review.

If you're using diltiazem to treat anal fissures, speak to your doctor who may suggest an alternative medicine.

Diltiazem and breastfeeding

If your doctor or health visitor says your baby is healthy, you can take diltiazem while breastfeeding.

There is not much information about using diltiazem while breastfeeding, but some information shows that it passes into breast milk in tiny amounts. It's unlikely to harm your baby. However, your doctor might suggest an alternative medicine that we know more about.

If you use the cream or ointment, make sure that you've washed your hands before picking up your baby.

If you do breastfeed while taking diltiazem and you notice that your baby is not feeding as well as usual, seems unusually sleepy, looks paler than usual, or if you have any other concerns about your baby, then talk to your health visitor midwife, pharmacist or doctor as soon as possible.

Diltiazem and fertility

Diltiazem may affect male fertility. There's no evidence that diltiazem affects fertility in women.

If you're trying for a baby, or having problems getting pregnant while taking diltiazem, then speak to your doctor.

Meds New IA (H2) - Pregnancy non-urgent care card

Tell your doctor if you're:

  • trying to get pregnant
  • pregnant
  • breastfeeding

Cautions with other medicines

There are some medicines that may affect how 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 or pharmacist before starting diltiazem if you're taking any other medicines, including:

These are not all the medicines that may cause problems if you take them with diltiazem. For a full list, see the leaflet inside your medicine packet.

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 remedy taken for depression. It's thought to affect the way diltiazem works.

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

There's not enough information to say that other complementary medicines, herbal remedies and supplements are safe to take with diltiazem. They're not tested in the same way as pharmacy and prescription medicines. They're generally not tested for the effect they have on other medicines.

Meds New IA (H2) - Cautions with other medicines alert

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

Content supplied by the NHS website

Content supplied by the NHS website, refreshed 19 August 2026. View the original NHS article ↗

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