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Generic name: diltiazem (oral/injection) [ dil-TYE-a-zem ]
Brand names: Cardizem, Cardizem CD, Cardizem LA, Cartia XT, Dilt-XR, ... show all 9 brands
Drug classes: Calcium channel blockers, Group IV antiarrhythmics

Medically reviewed by Kaci Durbin, MD. Last updated on Aug 6, 2023.

What is diltiazem?

Diltiazem belongs to a class of medications called calcium-channel blockers. It works by relaxing the blood vessels so the heart does not have to pump as hard. Diltiazem also increases the supply of blood and oxygen to the heart.

Diltiazem oral is used in adults alone or in combination with other medicines to treat hypertension (high blood pressure) or symptoms of angina (chest pain). Lowering blood pressure may lower your risk of a stroke or heart attack.

Diltiazem injection is used in adults to treat certain heart rhythm disorders such as atrial fibrillation or atrial flutter, or dangerously rapid heartbeats (tachycardia).

Diltiazem side effects

Get emergency medical help if you have signs of an allergic reaction to diltiazem (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Diltiazem may cause serious side effects. Call your doctor at once if you have:

Common diltiazem side effects may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Before taking this medicine

You should not use diltiazem if you are allergic to it, or if you have:

You may not be able to use diltiazem if you have:

To make sure this medicine is safe for you, tell your doctor if you have ever had:

It is not known whether diltiazem will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

Tell your doctor if you are breastfeeding.

How should I use diltiazem?

Use diltiazem exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.

Diltiazem injection is given into a vein by a healthcare provider. Your heart rate will be constantly monitored using an electrocardiogram or ECG (sometimes called an EKG). Your blood pressure and other vital signs will also be watched closely.

Diltiazem oral is taken by mouth. Your pharmacist can provide more information about how to take this medicine correctly.

Your dose needs may change if you switch to a different brand, strength, or form of this medicine.

Some forms of diltiazem oral cannot be crushed or chewed, and some forms can be opened and mixed with applesauce. Ask your pharmacist how to take this medicine.

Your blood pressure and liver function will need to be checked often.

If you have high blood pressure, keep using this medicine even if you feel well. High blood pressure often has no symptoms.

Store at room temperature away from moisture, heat, and light.

What happens if I miss a dose?

Diltiazem injection is used when needed and does not have a daily dose. Call your doctor if the medicine is not effective.

Take diltiazem oral as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include low blood pressure, slow heart rate, severe dizziness, or fainting.

What should I avoid while using diltiazem?

Avoid drinking alcohol while taking diltiazem extended-release capsules. Drinking alcohol with this medicine can cause side effects.

Avoid taking an herbal supplement containing St. John's wort.

Avoid getting up too fast from a sitting or lying position, or you may feel dizzy. Avoid driving or hazardous activity until you know how this medicine will affect you. Your reactions could be impaired.


You should not use diltiazem if you have very low blood pressure, a serious heart condition such as "sick sinus syndrome" or "AV block" (unless you have a pacemaker), or if you have recently had a heart attack and you have a build-up of fluid in your lungs.

Before taking this medicine, tell your doctor if you have kidney disease, liver disease, or congestive heart failure.

Diltiazem may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert. Do not stop taking this medication without first talking to your doctor. If you stop taking it suddenly, your condition may become worse.

Diltiazem may be only part of a complete program of treatment that also includes diet, exercise, and other medications. Follow your diet, medication, and exercise routines very closely.

If you are being treated for high blood pressure, keep using this medicine even if you feel well. High blood pressure often has no symptoms. You may need to use blood pressure medicine for the rest of your life. However, if you have symptoms of low blood pressure (dizziness, fainting, weakness, or blurred vision), call your doctor and stop taking diltiazem.

What other drugs will affect diltiazem?

Sometimes it is not safe to use certain medicines at the same time. Some drugs can affect your blood levels of other drugs you use, which may increase side effects or make the medicines less effective.

Many drugs can interact with diltiazem. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all other medicines you use.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use diltiazem only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.