Key takeaways

Diltiazem is a medication used to treat high blood pressure and prevent chest pain. It can cause side effects such as peripheral edema (swelling of the extremities), hypotension (low blood pressure), fatigue, and serious heart-related issues.
Weight gain associated with diltiazem is due to fluid retention and is not a direct side effect. However, sudden weight gain could be a sign of heart failure and requires prompt medical consultation.
The most common side effect of diltiazem injections is low blood pressure, occurring in 7% of patients, while oral diltiazem’s common side effects include swelling, headache, and dizziness.
Long-term use of diltiazem is considered safe, but it requires caution in patients with preexisting heart conditions and in interactions with other drugs.

Diltiazem is a generic prescription tablet or capsule used to treat high blood pressure and prevent chest pain (angina). Diltiazem injections are given to people during medical emergencies involving serious heart rate abnormalities: atrial fibrillation or paroxysmal supraventricular tachycardia. Some people are prescribed diltiazem in one of its brand-name versions: Cardizem, Cardizem CD, Cardizem LA, or Cartia XT. A calcium channel blocker, diltiazem partly blocks the ability of blood vessels and the heart to contract. This widens blood vessels, slows the heart, and reduces the force in each heartbeat. The combined effect is to lower blood pressure. Diltiazem can also have unwanted effects, including adverse effects on the heart.

Common side effects of diltiazem

The most common side effect of oral diltiazem is swelling due to fluid retention (edema), particularly in the hands, feet, and lower legs. However, low blood pressure is the most common side effect of a diltiazem injection. In order of incidence, the most common side effects of diltiazem are:

Swelling of the extremities (peripheral edema)
Headache
Dizziness
Fatigue
Slow heart rate
Flushing
Heart block
Low blood pressure
Acid indigestion
Constipation
Nausea
Liver problems
Skin rash

In clinical trials, people taking immediate-release diltiazem had a lower incidence of most of these side effects in comparison to people taking extended-release diltiazem.

Serious side effects of diltiazem

The most serious side effects of diltiazem include:

Slowed heart rate (bradycardia)
Heart block (AV block)
Heart rhythm problems (arrhythmias)
Severe low blood pressure
Heart failure
Severe allergic reactions

Weight gain

Weight gain is not a side effect of diltiazem. However, fluid retention is. Excess water can increase weight, but it’s only water weight. It will go away when the drug is stopped, or the edema is treated. However, a sudden gain in weight can be a sign of fluid retention due to congestive heart failure, so contact the prescriber or other healthcare professional if there’s a big gain in weight when taking diltiazem.

Hypotension

Low blood pressure is a very uncommon side effect in people taking diltiazem orally. However, low blood pressure is the most common side effect in people receiving diltiazem IV injections, occurring in 7% of patients. Nearly half will show symptoms. Unlike oral formats, however, diltiazem injections are used in critical situations involving serious heart rhythm problems. In these cases, patients are in an emergency or intensive care situation, so doctors and other healthcare professionals are monitoring blood pressure and will intervene if blood pressure drops. For people taking oral diltiazem, if low blood pressure is a problem, talk to the prescriber. The doses may need to be changed.

Fatigue

Asthenia is a common side effect of diltiazem. “Asthenia” is like fatigue, except that it’s a feeling of being worn out without actually working hard or exercising. It’s more commonly experienced in people taking extended-release diltiazem—about 3 in every 100. The incidence drops to 1 in 100 in people taking immediate-release diltiazem. Weakness, tiredness, and fatigue are not necessarily health-threatening side effects. However, if diltiazem-induced fatigue is interfering with daily life, talk to the prescribing healthcare provider about treatment options.

Hair loss

Hair loss has been reported in people taking diltiazem, but the incidence may be close to zero or as high as 2%. The nature of the hair loss has not been defined. If hair loss or thinning occurs when taking diltiazem, it may be caused by the drug or it may be an allergic or skin reaction to the drug. Contact the prescriber, particularly if there are other symptoms of a skin reaction, including rash or hives.

Side effects of diltiazem in elderly people

Diltiazem may not be appropriate for elderly people, particularly those with heart failure. There are several potential problems: increased risk for side effects, increased risk for falls and injuries, fluid retention, heart problems, and problems with mental function. In general, healthcare professionals will start older adults at a low dose. In others, healthcare providers may use a different calcium channel blocker that does not have strong effects on the heart or switch to another blood pressure medication.

How soon do diltiazem side effects start?

Diltiazem begins to work with the first dose. A dose of immediate-release diltiazem starts working in 30 to 60 minutes, while extended-release diltiazem begins working in about two to three hours. Many mild or moderate side effects could begin by then, including headache, dizziness, and nausea. Some serious side effects such as heart rhythm problems could also occur early in treatment. Other side effects such as fatigue and edema may require a few days or weeks of treatment before becoming a problem. Some allergic reactions, such as severe skin reactions, could also take some time before symptoms appear.

How long do diltiazem side effects last?

Diltiazem tablets and capsules are intended for long-term use. Some side effects will improve over time. However, once the drug is stopped, side effects will usually resolve. This can take about a day for immediate-release diltiazem and about twice that for extended-release diltiazem. Some side effects, though, may take longer to get better, including severe allergic reactions or heart problems. Some of the worst side effects, such as heart failure, may have lifelong consequences.

What are the long-term side effects of diltiazem?

Diltiazem is typically prescribed for months or years. There are no side effects due to long-term administration according to one study, so long-term use is considered safe.

Diltiazem contraindications

Because of its effects on the heart, diltiazem can significantly worsen serious heart problems. For this reason, diltiazem is never used in people with:

Second- to third-degree heart block unless a pacemaker is implanted
Sick sinus syndrome (a defect in the heart’s natural pacemaker) without an implanted pacemaker
Acute heart attack accompanied by fluid in the lungs (pulmonary congestion)
Low blood pressure
Allergies to the drug

Although diltiazem IV injections are used to treat atrial fibrillation and atrial flutter, there are certain cases of Afib in which the injection is contraindicated except in facilities that allow for monitoring and resuscitation.

Pregnancy

The safety of diltiazem, when given to pregnant women, has not been studied, but the risk is considered low. Healthcare providers are urged to be cautious when prescribing this drug during pregnancy or to use other treatment options.

Breastfeeding

Diltiazem is present in human breast milk, but the risk to the nursing infant is unknown. The FDA urges any prescribing healthcare provider to advise mothers prescribed diltiazem to use an alternative to breastfeeding.

Children

The Food and Drug Administration (FDA) has not approved diltiazem for use in children or adolescents, though some healthcare providers will prescribe it off-label to treat hypertension in pediatric patients.

Diltiazem warnings

Diltiazem can have significant effects on the heart and blood pressure, so there are several situations that require caution.

Cautions

Some heart conditions could be worsened by diltiazem, so the drug is either avoided or used with caution and extra monitoring in people with:

Heart conduction disorders such as heart block
Heart failure
Problems with the left ventricle of the heart
Liver disease
Gastroesophageal reflux disease (GERD)

Abuse and dependence

Healthcare professionals do not consider diltiazem to carry any risk of abuse or physical dependence.

Overdose

Get medical attention or call a poison control center if too much diltiazem is taken. An overdose can cause heart problems such as slow heart rate, low blood pressure, bad dizziness, fainting, heart block, or even cardiac failure.

Diltiazem interactions

Diltiazem has some potentially hazardous drug interactions. The most important are drugs that affect the heart. For this reason, the ulcer drug cisapride and the antipsychotic medication thioridazine are never prescribed with diltiazem.

Other drugs that affect the heart or lower blood pressure can be used, but with care and monitoring. These include:

Heart rhythm and heart rate drugs (antiarrhythmics) such as quinidine
Beta blockers such as Lopressor (metoprolol) and propranolol
Antipsychotics
Azole antifungal medications
Digitalis drugs such as digoxin
Nitroglycerin drugs
Benzodiazepines, particularly Halcion (triazolam) and midazolam
Niacin

Diltiazem can block the ability of the liver to break down certain types of drugs. These drugs can then build up in the body, so there’s an increased risk of side effects. On the other hand, some drugs block the liver’s ability to break down diltiazem, again raising the risk of side effects. These two types of drugs include:

Opioids
Some types of anticonvulsants such as carbamazepine
Buspirone
Some types of immune-suppressing drugs such as cyclosporine
HIV/AIDS drugs

Some drugs such as the tuberculosis drug rifampin or the supplement St. John’s wort speed up the body’s metabolism of diltiazem, reducing its effectiveness at lowering blood pressure. Drugs that raise blood pressure also reduce diltiazem’s effectiveness. These include stimulants, ADHD drugs, migraine drugs, NSAIDs, over-the-counter decongestants, and caffeine.

How to avoid diltiazem side effects

Diltiazem is an effective drug at controlling blood pressure, so it pays to prevent or manage some of the more common side effects. Here are a few tips.

1. Take diltiazem as prescribed

One of the best ways of maximizing the benefits of diltiazem treatment while minimizing the downside is to follow all the instructions given by the prescriber or written on the prescription label. For diltiazem, take this medicine at the same time every day. Don’t miss a dose. Diltiazem is taken once, twice, or three times daily, so use an alarm or app to remember each dose. If a dose is missed, take it when remembered. However, if the time for taking the next dose is near, then take that dose on time and skip the missed dose.

2. Make sure the prescriber has a complete medical history

Another sure way to minimize side effects is to tell the prescribing healthcare provider about all medical conditions, particularly:

Low blood pressure
Heart problems
Heart failure
Liver problems
GERD
Pregnancy or pregnancy plans
Breastfeeding or breastfeeding plans

Make sure the prescriber is also aware of all medications being taken. This includes not only prescription drugs but also over-the-counter medications and dietary supplements, as well.

3. Avoid alcohol

To prevent feeling tired or fatigued, it’s a good idea to either avoid drinking or not drink much. The same applies to using any drugs that can cause sleepiness like antihistamines.

4. Avoid driving and other risky activities

To prevent injuries or accidents, avoid driving, operating machinery, or other risky activities until certain that diltiazem is not causing fatigue or dizziness that can impair alertness.

5. Stand up slowly

Some people taking diltiazem may feel dizzy when standing up. To avoid this, stand up slowly. Sit down when feeling dizzy.

How to treat side effects of diltiazem

Not everyone will have problems with diltiazem. But, for those who do, there are ways to manage the side effects. Some adverse effects, though, may require medical attention.

Peripheral swelling

Elevate the feet to help reduce the swelling. If swelling persists or gets worse, talk to the prescribing healthcare provider.

Headache

Take a pain reliever such as acetaminophen. NSAIDs like aspirin or ibuprofen raise blood pressure. If headaches persist or get worse, talk to the prescribing healthcare provider.

Stomach pain

For severe stomach pain, get immediate medical attention.

Low blood pressure

Lightheadedness, dizziness, and fainting are signs that blood pressure is too low. Call a healthcare professional or get medical attention.

Heart problems

Contact a healthcare professional if you experience heart palpitations, heart rhythm abnormalities, or a slow heartbeat.

Liver problems

Diltiazem can cause serious liver problems. Contact a healthcare professional if any symptoms of liver disease are noticed, including:

Dark urine
Pale stools
Throwing up
Loss of appetite
Feeling tired
Yellowing of the skin or eyes

Allergic reactions

A hypersensitivity reaction or skin reaction to this drug will require immediate medical attention. Do not take another dose. Symptoms of a severe allergic or drug reaction include skin rash, hives, swelling of the face, mouth, or neck, trouble breathing, sore throat, fever, chills, skin peeling, skin blistering, skin pain, burning eyes, or sores in the mouth, nose, or throat.

Diltiazem side effects and how to avoid them