Updated: January 25, 2026

What Is Diltiazem XR? Uses, Dosage, and What You Need to Know in 2026

Author

Peter Daggett

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What Is Diltiazem XR?
What Is Diltiazem XR Used For?
What Dosage Forms and Strengths Are Available?
How Is Diltiazem XR Dosed?
How to Take Diltiazem XR Correctly
Who Should NOT Take Diltiazem XR?

What is Diltiazem XR? Learn about its uses, dosage forms, how to take it, what to avoid, and what makes it different from other heart medications in 2026.

Diltiazem XR is an extended-release formulation of diltiazem hydrochloride, a medication that has been helping patients manage heart-related conditions for over four decades. If you've been prescribed Diltiazem XR — or are wondering whether it might be right for you — here's a comprehensive, plain-English guide to everything you need to know.

What Is Diltiazem XR?

Diltiazem XR is a prescription calcium channel blocker, specifically a non-dihydropyridine (non-DHP) type in the benzothiazepine chemical class. It was first approved by the FDA in 1982 and has been one of the most widely prescribed heart medications in the world ever since.

The "XR" stands for extended-release, meaning the drug is slowly released into your body over 24 hours — making once-daily dosing possible, versus immediate-release diltiazem which requires 3–4 doses per day.

Brand names include Cardizem CD, Cardizem LA, Cartia XT, Dilacor XR, Dilt-XR, Tiazac, Taztia XT, and Matzim LA. Generic versions are widely available and significantly less expensive.

What Is Diltiazem XR Used For?

The FDA has approved Diltiazem XR (oral extended-release) for two main conditions:

Hypertension (high blood pressure) — Diltiazem XR relaxes blood vessel walls, reducing the resistance the heart must pump against. It is effective as monotherapy or in combination with other blood pressure medications.

Chronic stable angina (chest pain) — By reducing the heart's workload and oxygen demand, Diltiazem XR reduces the frequency and severity of angina episodes. It is used for both effort-related angina and vasospastic (Prinzmetal's) angina.

Off-label uses (not FDA-approved but supported by clinical evidence) include:

Rate control in atrial fibrillation (AF) and atrial flutter (more commonly managed with IV diltiazem in acute settings)

Migraine prophylaxis (prevention)

Pulmonary hypertension (selected patients with positive vasoreactivity testing)

What Dosage Forms and Strengths Are Available?

Diltiazem XR comes in two main forms:

Extended-release capsules (Cardizem CD-type, Cartia XT-type, Dilacor XR-type, Tiazac-type): 120 mg, 180 mg, 240 mg, 300 mg, 360 mg

Extended-release tablets (Cardizem LA-type, Matzim LA): 120 mg, 180 mg, 240 mg, 300 mg, 360 mg, 420 mg

Important: These formulation types are NOT interchangeable. Pharmacists cannot substitute one for another without a new prescription from your doctor.

How Is Diltiazem XR Dosed?

Dosing varies by formulation type and condition:

Hypertension: Starting dose usually 180–240 mg once daily; maximum dose 540 mg/day; titrate at 2-week intervals

Chronic stable angina: Starting dose usually 120–180 mg once daily; maximum dose 480 mg/day; titrate at 7–14 day intervals

How to Take Diltiazem XR Correctly

Take once daily at approximately the same time each day

Swallow capsules or tablets whole — never crush, chew, or break them. Breaking them destroys the extended-release mechanism.

Dilt-XR capsules specifically should be taken on an empty stomach in the morning

Avoid grapefruit juice — it interferes with CYP3A4 metabolism and can raise diltiazem blood levels dangerously

Do not stop taking Diltiazem XR without talking to your doctor first

Who Should NOT Take Diltiazem XR?

Diltiazem XR is contraindicated in patients with:

Sick sinus syndrome (unless they have a functioning pacemaker)

Second- or third-degree AV block (unless they have a functioning pacemaker)

Severely low blood pressure (systolic below 90 mmHg)

Acute myocardial infarction with pulmonary congestion

Known hypersensitivity to diltiazem

For a full list of drug interactions to discuss with your doctor, see Diltiazem XR Drug Interactions: What to Avoid and What to Tell Your Doctor.

If you're having trouble filling your prescription, use medfinder to find pharmacies near you with your exact formulation in stock.

Frequently Asked Questions

Diltiazem XR is FDA-approved for two conditions: hypertension (high blood pressure) and chronic stable angina (chest pain). Off-label uses include rate control in atrial fibrillation and atrial flutter, migraine prophylaxis, and certain cases of pulmonary hypertension. It works by blocking calcium channels in heart muscle and blood vessel walls.

These are all diltiazem extended-release products, but they use different release mechanisms and are not interchangeable. Cardizem CD is a once-daily capsule formulation, Cardizem LA is a once-daily tablet formulation, and generic 'Diltiazem XR' or 'Diltiazem ER' may refer to either capsule or tablet types depending on what your pharmacy stocks. Ask your doctor or pharmacist which specific type you have been prescribed.

For blood pressure control, Diltiazem XR typically begins lowering blood pressure within 1–2 hours of the first dose. Optimal blood pressure reduction is usually achieved within 2 weeks. For angina prevention, patients often notice a reduction in angina frequency within the first week of therapy.

Diltiazem XR can be combined with some other blood pressure medications, but not all. It should generally NOT be combined with beta-blockers or digoxin without careful monitoring, as all three slow heart rate and can cause dangerous bradycardia or heart block when used together. Always tell your doctor and pharmacist about all medications you take before starting or changing diltiazem XR.

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