Diltiazem: what it treats, how to take it, side effects
Last updated September 3, 2026.
Diltiazem is a calcium channel blocker that relaxes blood vessels and increases blood and oxygen supply to the heart. You may know it as Cardizem or Tiazac. It covers high blood pressure and angina, and it comes in enough forms that the pharmacist's instructions matter as much as the prescription.
What does it treat?
High blood pressure and angina (chest pain). MedlinePlus also lists certain abnormal heart rhythms as another use. One distinction to know: taken regularly, it controls chest pain - it does not stop chest pain already happening. Your doctor prescribes a different medication for that.
How do you take it?
The regular tablet is taken three or four times a day; the extended-release tablet or capsule once or twice a day, same times every day. Ask your pharmacist whether your specific product goes with or without food - the instructions genuinely vary by product. Swallow extended-release tablets and capsules whole, never chew or crush them. Your doctor starts low and increases gradually - no more than once every 1 to 2 days for the regular tablet, every 7 to 14 days for extended-release. Full benefit takes up to 2 weeks. Keep taking it even when you feel well, and never stop without your doctor. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: dizziness or lightheadedness, flushing, headache, weakness, slow heartbeat, vomiting, diarrhea, constipation, nasal congestion, and cough.
- Serious: swelling of the face, eyes, lips, tongue, hands, arms, feet, ankles, or lower legs; trouble breathing or swallowing; fainting; rash; and the liver-injury cluster - yellowing skin or eyes, nausea, extreme tiredness, unusual bleeding or bruising, lack of energy, loss of appetite, upper right stomach pain, flu-like symptoms. And a specific one: an increase in the frequency or severity of chest pain means calling the doctor immediately.
Who should not take it?
Flag heart failure, a slow heart rate or heart-rhythm problems, low blood pressure, and liver or kidney disease. It can make you dizzy - stand slowly, and no driving until you know how it affects you. Tell the surgeon or dentist before any procedure. Pregnancy and breastfeeding need a direct call with your doctor.
When is it an emergency?
Call 911 for fainting, worsening chest pain, or trouble breathing or swallowing. Yellowing skin or eyes with upper right stomach pain and extreme tiredness mean immediate care. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why does my pharmacist keep asking which diltiazem product I take?
Because the products genuinely differ. MedlinePlus says to ask your pharmacist whether your product is taken with or without food, because instructions vary with each product - and the regular tablet is three to four times a day while the extended-release forms are once or twice. Same drug name, different rules. When you refill, confirm the product matches what you had.
Can diltiazem stop chest pain once it starts?
No. MedlinePlus says taken regularly it may control chest pain, but it does not stop chest pain once it starts - your doctor prescribes a separate fast-acting medication for attacks. And an increase in the frequency or severity of chest pain while on diltiazem is an immediate call to your doctor.
How is diltiazem different from amlodipine?
Both are calcium channel blockers, but they lean different directions. Amlodipine works mostly on the blood vessels; diltiazem also slows the heart and its electrical activity, which is why it gets used for certain abnormal heart rhythms and why a slow heartbeat is on its common side effect list.
Can I drink alcohol while taking diltiazem?
Neither the label nor MedlinePlus gives diltiazem-specific alcohol language. Alcohol dilates blood vessels and drops pressure on its own, which stacks with what this drug does - the dizziness risk climbs. Keep it light and ask your doctor for the personal rule.
Why are my ankles swelling on diltiazem?
Swelling of the feet, ankles, or lower legs is on MedlinePlus's serious list for diltiazem - dilated vessels leak a little fluid into tissues. It is worth a prompt call to your doctor, since the fix may be a dose change or a companion medication, not just putting your feet up.
What happens if I miss a dose of diltiazem?
Take it as soon as you remember, unless it is almost time for the next one - then skip it and never double up. With the 3-to-4-times-daily regular tablet, meal-anchoring the doses keeps the rhythm; with once-daily extended-release, pair it with breakfast.