Cardizem Drug Interactions You Need to Know About

If you take Cardizem (Diltiazem), it's important to know which medications, supplements, and foods can interact with it. Diltiazem is metabolized by the liver enzyme CYP3A4, and it also inhibits that same enzyme — which means it can both be affected by other drugs and change how other drugs work in your body.

Some interactions are minor nuisances. Others can be genuinely dangerous. This guide breaks down the major and moderate drug interactions with Cardizem so you can have an informed conversation with your doctor and pharmacist.

How Drug Interactions Work

A drug interaction happens when one substance changes how another substance works in your body. There are a few ways this can happen:

• Metabolism interference: Many drugs are broken down by the same liver enzymes. When two drugs compete for the same enzyme (especially CYP3A4), one or both can build up to higher-than-expected levels in your blood, increasing the risk of side effects.
• Additive effects: If two drugs have similar effects (for example, both slow heart rate), combining them can amplify that effect to a dangerous degree.
• Opposing effects: Some drugs can counteract each other, making one or both less effective.

Cardizem is involved in all three types. It's both a substrate of CYP3A4 (meaning CYP3A4 breaks it down) and a moderate inhibitor of CYP3A4 (meaning it slows down the breakdown of other drugs processed by that enzyme). This dual role is what gives it such a long list of interactions.

Medications That Interact With Cardizem

Major Interactions — Avoid or Use With Extreme Caution

These combinations are potentially dangerous and should generally be avoided unless your doctor specifically decides the benefit outweighs the risk, with close monitoring.

• Beta-blockers (Metoprolol/Lopressor/Toprol XL, Atenolol/Tenormin, Propranolol/Inderal, Carvedilol/Coreg) — Both Cardizem and beta-blockers slow the heart rate and reduce the force of heart contractions. Together, they can cause severe bradycardia (dangerously slow heart rate), AV block, and heart failure. IV beta-blockers with Cardizem are especially dangerous and should never be combined. Oral combinations are sometimes used under close monitoring, but this requires careful dose management.
• Digoxin (Lanoxin) — Cardizem increases Digoxin blood levels by 20-50%. Since Digoxin has a narrow therapeutic window (the difference between an effective dose and a toxic dose is small), this can lead to Digoxin toxicity, with symptoms like nausea, vomiting, visual disturbances (yellow-tinted vision), and dangerous heart rhythm changes. Your doctor should monitor Digoxin levels closely.
• Simvastatin (Zocor) and Lovastatin (Mevacor) — Cardizem inhibits CYP3A4, which is the enzyme that breaks down these statins. The result is significantly higher statin levels in your blood, which increases the risk of rhabdomyolysis — a serious condition where muscle tissue breaks down and can damage the kidneys. If you take Cardizem, your doctor should limit Simvastatin to 10 mg/day or switch to a statin that doesn't use CYP3A4 (like Rosuvastatin or Pravastatin).
• Cyclosporine (Sandimmune, Neoral, Gengraf) — Cardizem significantly increases Cyclosporine blood levels through CYP3A4 inhibition. This raises the risk of Cyclosporine toxicity, including kidney damage. Cyclosporine levels must be monitored closely if both drugs are used together.
• Carbamazepine (Tegretol) — Cardizem raises Carbamazepine levels, potentially causing toxicity with symptoms like dizziness, double vision, unsteadiness, and nausea. Blood level monitoring is essential.
• Lithium — Combining Diltiazem with Lithium can increase the risk of neurotoxicity, causing symptoms like tremors, confusion, and muscle weakness. Lithium levels should be monitored.
• Rifampin (Rifadin) — This goes the other direction: Rifampin is a powerful CYP3A4 inducer that can dramatically reduce Diltiazem levels in your blood, potentially making Cardizem ineffective. This combination should generally be avoided.

Moderate Interactions — Use With Caution

These combinations may require dose adjustments or extra monitoring, but are sometimes used together when clinically appropriate.

• Benzodiazepines — specifically Midazolam (Versed) and Triazolam (Halcion). Cardizem can increase blood levels of these sedatives through CYP3A4 inhibition, leading to excessive sedation, drowsiness, and respiratory depression. Doses may need to be reduced.
• Buspirone (Buspar) — Cardizem increases Buspirone levels, potentially causing more dizziness and drowsiness.
• Cimetidine (Tagamet) — This heartburn medication inhibits the enzymes that break down Diltiazem, which can raise Cardizem levels in your blood and increase the risk of side effects like low blood pressure and slow heart rate.
• Quinidine — Both drugs have cardiac effects. Combining them increases the risk of dangerous heart rhythm changes.
• Amiodarone (Cordarone, Pacerone) — Both Amiodarone and Cardizem slow heart rate and AV node conduction. Together, they can cause severe bradycardia and AV block. This combination requires very careful monitoring.

Supplements and Over-the-Counter Drugs to Watch Out For

It's not just prescription drugs you need to worry about. Several common supplements and OTC products can interact with Cardizem:

• St. John's Wort — This popular herbal supplement is a CYP3A4 inducer, similar to Rifampin. It can reduce Diltiazem levels in your blood, making it less effective. Avoid this combination.
• Calcium supplements — While it may seem counterintuitive, oral calcium supplements at normal doses don't meaningfully interfere with calcium channel blockers. However, IV calcium can reverse the effects of Diltiazem in emergency settings.
• NSAIDs (Ibuprofen/Advil/Motrin, Naproxen/Aleve) — NSAIDs can reduce the blood pressure-lowering effect of Cardizem and increase the risk of kidney problems, especially in older adults. Use the lowest dose for the shortest time, and talk to your doctor about alternatives like Acetaminophen (Tylenol).
• Antacids — Most antacids don't significantly interact with Diltiazem, but Cimetidine (Tagamet) does (see above). Other H2 blockers like Famotidine (Pepcid) are generally safer choices.

Food and Drink Interactions

Grapefruit and Grapefruit Juice

Avoid grapefruit while taking Cardizem. Grapefruit inhibits CYP3A4 in your intestines, which can significantly increase how much Diltiazem your body absorbs. This can raise blood levels of the drug, increasing the risk of side effects like low blood pressure, excessive heart rate slowing, and dizziness. Even one glass of grapefruit juice can have an effect.

Alcohol

Alcohol can enhance the blood pressure-lowering effects of Cardizem. Drinking while taking Diltiazem may cause your blood pressure to drop more than expected, leading to dizziness, lightheadedness, or fainting. If you drink, do so in moderation and be aware of how you feel — especially when standing up.

Food Timing

Immediate-release Cardizem tablets are typically taken before meals. Extended-release formulations can generally be taken with or without food, though taking them consistently (always with food or always without) helps maintain steady drug levels.

What to Tell Your Doctor

Before starting Cardizem — and at every follow-up visit — make sure your doctor and pharmacist know about:

• Every medication you take, including prescriptions, over-the-counter drugs, and herbal supplements. Don't assume something is too "minor" to mention.
• Any new medications started since your last visit — even if another doctor prescribed them.
• Any symptoms that could signal an interaction: new or worsening dizziness, extreme fatigue, very slow heart rate (below 50 bpm), muscle pain or weakness (especially if you take a statin), confusion, or visual changes.
• If you're planning surgery. Anesthesiologists need to know about Cardizem because it can interact with anesthesia drugs and affect heart rate during procedures.

Your pharmacist is also a valuable resource. They can run an interaction check on your full medication list whenever you start a new drug — and many will do this automatically when filling prescriptions.

Final Thoughts

Cardizem (Diltiazem) has a significant number of drug interactions — largely because of its role as both a CYP3A4 substrate and inhibitor. The most important ones to remember are beta-blockers (risk of severe bradycardia), statins like Simvastatin (risk of rhabdomyolysis), Digoxin (risk of toxicity), and grapefruit (increased drug levels).

Always keep your healthcare providers informed about everything you take. For more about Cardizem, see our guides on Cardizem side effects and what Cardizem is used for. To find Cardizem at the best price near you, visit Medfinder.