9 Diltiazem Side Effects: Headache, Constipation, and More

Diltiazem is a medication used to treat high blood pressure and chest pain. It belongs to a class called calcium channel blockers and goes by many brand names, including Cardiazem, Tiazac, and Cartia XT. Because of how it works, diltiazem can cause side effects such as constipation, swelling, and dizziness.

Some diltiazem side effects can be temporary and lessen over time as your body adjusts to the medication. But others, such as low blood pressure and a slow heart rate, are important to keep in mind — especially if your dosage is adjusted or other medications are added to your regimen.

Diltiazem side effects at a glance

Diltiazem side effects can range from mild to severe. Many can be managed at home. But more serious side effects that require medical attention are possible.

Common diltiazem side effects (reported by at least 2% of people during clinical trials) include:

• Runny nose

• Headache

• Sore throat

• Constipation

• Flu-like symptoms

• Swelling in the legs and ankles

• Muscle pain

• Dizziness

• Diarrhea

• Nausea

• Vomiting

• Sinus infections

• Back pain

• Feeling weaker than usual

Less common but serious diltiazem side effects include:

• Abnormally slow heart rate or heart block in certain people

• Worsening of heart failure

• Low blood pressure (hypotension)

• Liver problems

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Some diltiazem side effects may be more likely if you take it with interacting medications. Be sure to share your medication list with your healthcare team. That way, they can be managed before becoming an issue.

Below, we take a closer look at nine diltiazem side effects and tips for managing them.

1. Headache

Like other calcium channel blockers, diltiazem can cause headaches. This may be due to blood pressure changes from the medication. Often, this side effect subsides over time as your body adjusts to the treatment. Here are a few things you can do in the meantime:

• Rest and stay hydrated.

• Limit alcohol, which can worsen headaches.

• Ask your healthcare team about over-the-counter (OTC) pain relievers that may be safe for you to take, such as acetaminophen (Tylenol).

• Avoid certain activities or foods that seem to trigger or worsen your headaches.

But if headaches start interfering with your daily activities or don’t go away, tell your prescriber. It’s possible that they’re from diltiazem — or something else, such as hormonal changes. Your prescriber can help pinpoint the cause.

2. Dizziness

You may feel dizzy while taking diltiazem, especially as you start with the treatment. Dizziness can also happen if your blood pressure drops too low.

You may be more likely to feel dizzy when changing positions too quickly, such as going from sitting to standing. Try changing positions more slowly so your body has time to adjust. And if you don’t feel steady on your feet, sit or lie down. This can help you avoid falling.

EXPERT PICKS: WHAT TO READ NEXT

• Is this medication safe to take with diltiazem? Learn about potential diltiazem interactions and how to manage them.

• Alcohol and blood pressure medications: Get the details on why this can be a risky combination.

• What’s a typical dosage? Explore this guide for information on typical diltiazem dosages and what to do if you miss your dose.

Tell your prescriber if the dizziness is persistent or starting to interfere with your daily activities. 

Your dosage may need to be adjusted, or the medication may need to be stopped. But if you experience dizziness with fainting, chest pain, or irregular heartbeat, go to the ER.

3. Constipation

Diltiazem can cause constipation, which is another common calcium channel blocker side effect. If you become constipated, there are a few things you can do to get things moving again, including:

• Drink enough fluids throughout the day, since dehydration can worsen constipation.

• Incorporate more movement into your routine to help stimulate bowel movements.

• Introduce more fiber into your diet to help bulk up and soften your stools.

• Try OTC laxatives, but ask your healthcare team first.

If you’re unable to get relief, or if your constipation is severe, tell your prescriber. They may adjust your dosage or recommend an alternative heart or blood pressure medication that’s less likely to cause constipation.

4. Swelling

Diltiazem can cause swelling (edema) in your legs and ankles. This is more common with other calcium channel blockers, such as amlodipine (Norvasc). The risk of swelling tends to increase with higher doses and long-term use.

There are a few things you can do to help lessen leg swelling during treatment:

• Wear compression socks to support circulation and reduce fluid buildup.

• Elevate your legs above heart level when sitting or lying down, as directed by your healthcare team.

• Avoid prolonged standing or sitting to reduce pooling of fluid in your extremities.

If these strategies don’t seem to help, your prescriber may consider lowering your dose or switching you to a different medication.

5. Stuffy nose

Diltiazem can cause nasal congestion in some people. In most cases, you can manage this side effect at home:

• Use a saline spray.

• Try steam inhalation or a humidifier.

• Elevate your head while sleeping.

A pharmacist can also recommend some OTC decongestants. But it’s important to know that some decongestants are not recommended for people with high blood pressure. Plus, using nasal decongestants longer than 3 days can make your stuffy nose worse.

6. Low blood pressure

Since diltiazem can lower your blood pressure, there’s a chance it may drop too low. This risk goes up if you take diltiazem with other medications that lower blood pressure.

If your blood pressure drops too low, you may experience symptoms such as:

• Dizziness or lightheadedness

• Weakness or unusual tiredness

• Blurred vision

If you experience these symptoms, sit or lie down immediately to prevent falls and injury. Tell your healthcare team right away if these symptoms persist. They may need to adjust your dose or medications.

Get emergency medical care if you experience symptoms such as:

• Feeling like you’re going to pass out or actually fainting

• Severe dizziness or inability to stand

• Chest pain

• Slow, irregular, or pounding heartbeat

• Shortness of breath

• Severe weakness of confusion

7. Slow heart rate

Diltiazem blocks certain calcium channels in the heart, which slows down the electrical signals that control your heartbeat. This helps lower your heart rate to reduce the workload on your heart.

But this can also increase the risk of your heart beating too slowly, especially if you have problems with your heart’s electrical system or take higher doses. Taking diltiazem with other medications that slow your heart rate, such as beta blockers, also increases this risk.

A slow heart rate isn’t always cause for concern. But if you develop symptoms such as excessive fatigue or shortness of breath, tell your prescriber. This could indicate that your diltiazem dose is too high.

8. Liver problems

Diltiazem can occasionally cause elevations in liver enzymes, a potential sign of liver inflammation or damage. In most cases, these changes are temporary and don’t cause noticeable symptoms. But your healthcare team may monitor your liver function during regular checkups to catch liver problems early.

More serious liver problems are rare, but they have been reported in people taking calcium channel blockers like diltiazem. This risk may be higher if you take other medications that can affect the liver. Contact your healthcare team if you notice any of these symptoms:

• Yellowing of your skin or eyes (jaundice)

• Unusual fatigue

• Nausea or vomiting

• Loss of appetite

• Dark-colored urine

• Persistent fever or rash

9. Worsening heart failure

Experts recommend that people with certain types of heart failure avoid calcium channel blockers like diltiazem since it can worsen symptoms without benefits.

If you have preexisting heart failure, or if you develop heart failure while taking diltiazem, make sure your healthcare team is aware. They can determine the best next steps and treatment options.

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Written by:

Sandy P. Bonfin, PharmD, BCPS

Sandy Bonfin, PharmD, BCPS, is a clinical pharmacist at a Florida hospital. Bonfin has worked in pediatric medicine, emergency medicine, internal medicine, and intensive care.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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