A rate-limiting calcium-channel blocker
Diltiazem
A "rate-limiting" calcium-channel blocker that relaxes vessels and slows the heart; modified-release brands are often not interchangeable.
What is Diltiazem?
Diltiazem is a rate-limiting calcium-channel blocker that both widens blood vessels and slows the heart. It is used to lower blood pressure, prevent angina, and help control certain fast or irregular heart rhythms.
Education and reference only. This is a plain-language guide to Diltiazem — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Diltiazem is a "rate-limiting" calcium-channel blocker. Unlike nifedipine, which mainly relaxes blood vessels, diltiazem both widens blood vessels and slows the heart, so it is used for high blood pressure, for angina, and to help control fast heart rates such as in atrial fibrillation. A practical quirk is important: there are many different modified-release brands of diltiazem, and they are not all interchangeable, so it is usually prescribed and dispensed by a specific brand name to keep treatment consistent.
How it works
Diltiazem blocks the calcium channels that muscle cells use to contract. In blood-vessel walls this relaxes and widens the vessels, lowering blood pressure; in the heart it slows the rate at which the heart's natural pacemaker fires and the speed at which signals pass through, which slows and steadies the heartbeat. This dual action — on both vessels and the heart's electrical system — is what sets the rate-limiting calcium-channel blockers apart from vessel-only ones like nifedipine and amlodipine.
Company & origin
Originated / developed by: Tanabe Seiyaku (now Mitsubishi Tanabe Pharma).
Diltiazem was discovered and developed by the Japanese company Tanabe Seiyaku (now Mitsubishi Tanabe Pharma) in the late 1960s/early 1970s. The benzothiazepine calcium-channel blocker was first launched in Japan in 1974 as Herbesser (Cardizem in the US).
What it treats
Conditions Diltiazem is used for
Practical use
How to take Diltiazem
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it as prescribed; modified-release forms should be swallowed whole and not crushed or chewed.
- Stick to the same brand if possible, as different versions can release the medicine differently.
- Be aware it can cause constipation, so keep well hydrated and eat plenty of fibre.
- Do not combine it with a beta-blocker without advice, as together they can slow the heart too much.
- Report a very slow heartbeat, marked dizziness, fainting or swollen ankles.
Weighing it up
Advantages & disadvantages of Diltiazem
Advantages
- Lowers blood pressure while also helping to control heart rate.
- Effective for angina and certain fast heart rhythms.
- Useful where both blood-pressure and rate control are wanted.
- Available in once-daily modified-release forms.
Disadvantages
- Can slow the heart too much, especially if combined with a beta-blocker.
- Commonly causes constipation and may cause ankle swelling.
- Different brands are not always interchangeable, which can cause confusion.
- Can interact with several other medicines, increasing their effects.
- May cause dizziness, headache or tiredness.
Practical use
Good to know
A key point is that the many modified-release brands of diltiazem are often not interchangeable, so prescriptions are usually written by brand and you should be kept on the same one rather than swapped between brands. Because diltiazem slows the heart, it should not be combined with a beta-blocker without specialist advice, as together they can slow the heart too much. Constipation is a recognised side effect. Modified-release forms should usually be swallowed whole. It can interact with several medicines (including raising levels of some statins), so the rest of your medicines are taken into account.
Who should not take it / use with caution
- People with certain slow or blocked heart rhythms, or significant heart failure with a weakened pump.
- People with very low blood pressure or certain unstable heart conditions.
- Used with great caution — and usually avoided — together with beta-blockers without specialist advice, as the heart can be slowed too much.
Monitoring
- Blood pressure and heart rate
- Heart rhythm where used for rate control
- For ankle swelling, constipation and tolerability
Side effects
- Slowing of the heart rate, and sometimes dizziness or tiredness.
- Ankle swelling, flushing and headache, particularly when starting.
- Constipation; uncommonly a very slow heart rate, or skin reactions.
Key interactions
- It must not usually be combined with a beta-blocker without specialist advice, as the heart-slowing effects add up.
- It raises the levels of some statins (such as simvastatin), limiting how much can be used together, and interacts with several other heart and other medicines.
- Grapefruit juice can raise its levels; tell your pharmacist about everything you take.
Available as: Immediate-release tablets and many modified-release brands (tablets and capsules) that are often not interchangeable — usually prescribed by brand and swallowed whole.
Answers
Diltiazem: frequently asked questions
Why is diltiazem prescribed by brand name?
Because the various modified-release versions of diltiazem release the drug differently and are not all interchangeable. To keep your treatment steady and predictable, prescribers usually specify a particular brand and keep you on the same one rather than switching between brands.
Can I take diltiazem with a beta-blocker?
Not without specialist advice. Both diltiazem and beta-blockers slow the heart, so combining them can slow it too much and cause problems. If you are prescribed both, it will be a deliberate, closely supervised decision — never something to start on your own.
What is the difference between diltiazem and nifedipine or amlodipine?
They are all calcium-channel blockers, but diltiazem is "rate-limiting" — it slows the heart as well as relaxing blood vessels — whereas nifedipine and amlodipine act mainly on blood vessels and do not slow the heart. This is why diltiazem can also be used to help control fast heart rhythms.
Does diltiazem cause constipation?
It can. Constipation is a recognised side effect of the rate-limiting calcium-channel blockers (diltiazem and verapamil), though it is usually milder with diltiazem than with verapamil. Plenty of fluids and fibre help; if it is troublesome, tell your pharmacist or prescriber.
What is the difference between diltiazem and Tildiem, Adizem or Cardizem?
They are the same medicine — diltiazem is the generic (active-ingredient) name, while Tildiem and Adizem are UK brand names and Cardizem is a US brand name. Because modified-release brands are not interchangeable, the specific brand you are given matters, even though the active ingredient is identical.
The wider class
About Calcium-channel blockers
Diltiazem belongs to the calcium-channel blockers class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Diltiazem hydrochloride.
- NICE NG136: Hypertension in adults.
- NICE CKS: Diltiazem.
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