Diltiazem is an oral calcium-channel blocker for adults with hypertension, angina, or selected fast heart-rhythm disorders. It helps relax blood vessels and slow cardiac activity, supporting blood-pressure control, angina prevention, and heart-rate management.
Diltiazem is an oral calcium-channel blocker supplied as capsules for adults with high blood pressure, angina, or selected fast heart-rhythm disorders. It reduces the force and speed of cardiac activity while relaxing blood vessels. This can lower blood pressure, reduce chest-pain episodes, and improve rate control.
Diltiazem is an oral calcium-channel blocker supplied as capsules for adults. It belongs to the benzothiazepine group and works by relaxing blood vessels while reducing the force and speed of cardiac activity. Capsules may use a modified-release design; follow the prescribed regimen and the exact details stated on the pack.
Diltiazem on this page is supplied as capsules for oral use. Capsules may use a modified-release design, which releases diltiazem gradually to maintain steadier blood concentrations through the day.
The prescribed regimen depends on the condition being treated, heart rate, blood-pressure response, kidney and liver function, and other cardiovascular medicines. A prescriber may alter the dose gradually rather than making large changes at once.
Use capsules in the following way:
Breaking a modified-release capsule can release diltiazem too quickly. That can increase the chance of low blood pressure, dizziness, or an excessively slow heart rate.
A missed dose should be taken when remembered unless the next scheduled dose is due soon. In that situation, skip the missed dose and continue with the normal schedule. Never take two doses together to compensate.
The MHRA identifies cardiovascular medicines as products where suspected adverse effects and serious medication incidents should be reported through the Yellow Card Scheme [3].
Diltiazem is a rate-limiting calcium-channel blocker. It blocks L-type calcium channels in cardiac muscle, the atrioventricular node, and vascular smooth muscle. Less calcium influx leads to slower electrical conduction, a lower heart rate in many patients, and relaxation of arteries.
Its effect differs from medicines that act mainly on blood vessels. Diltiazem has a stronger influence on heart rate and atrioventricular-node conduction than amlodipine or nifedipine. This makes it useful where raised blood pressure occurs alongside angina or a rate-control need.
The U.S. Food and Drug Administration describes diltiazem as a calcium-channel blocker that reduces calcium movement into muscle cells, producing vascular relaxation and cardiovascular effects [2].
Diltiazem belongs to the benzothiazepine group of calcium-channel blockers. It is used for hypertension, stable angina, and supraventricular arrhythmias where slowing electrical conduction through the heart is clinically appropriate.
Hypertension means that blood pressure remains raised over time, which places strain on arteries, the heart, kidneys, and brain. Diltiazem lowers pressure by relaxing arterial smooth muscle, allowing blood to pass with less resistance.
Angina occurs when the heart muscle does not receive enough oxygen-rich blood for its workload. Diltiazem can reduce angina by lowering heart rate, reducing contractile force, and widening coronary blood vessels.
Doctors may also use diltiazem for some supraventricular tachyarrhythmias. These are rhythm disturbances that begin above the heart’s ventricles. Slowing conduction through the atrioventricular node can help control an excessively fast pulse.
The benefit is preventive rather than immediate.
Diltiazem limits calcium entry into these cells, reducing vascular resistance and easing the heart’s workload [1].
Diltiazem is selected when blood-pressure control, angina prevention, and heart-rate effects need to be considered together. The best option depends on the diagnosed condition and the person’s pulse, cardiac function, and concurrent medicines.
| Treatment approach | Main cardiovascular action | Typical clinical fit |
|---|---|---|
| Diltiazem | Relaxes arteries and slows atrioventricular-node conduction | Hypertension or angina with a need for rate control |
| Amlodipine | Relaxes arteries with little direct effect on heart rate | Hypertension or angina when pulse slowing is not wanted |
| Beta-blocker therapy | Reduces heart rate and cardiac workload through beta receptors | Angina, some arrhythmias, or post-heart-attack care when suitable |
Amlodipine can be preferable for patients with a naturally slow pulse because it does not usually reduce heart rate to the same degree. Beta-blockers may be selected when there is a separate reason to reduce sympathetic stimulation, such as previous myocardial infarction.
Diltiazem is less suitable when impaired cardiac pumping function or conduction disease is present. The trade-off matters: its rate-limiting effect can be useful, yet it can also cause bradycardia in susceptible people.
The NHS Medicines A–Z guidance highlights the need to review other prescribed, non-prescribed, and herbal products when taking diltiazem [4].
This medication is not for you if you have had a serious allergic reaction to diltiazem or have specific heart-conduction problems without appropriate pacing support. It may also be unsuitable if you have a very slow pulse, very low blood pressure, acute heart failure with poor heart pumping function, or certain sick sinus problems.
Tell your doctor or pharmacist about all medicines, supplements, eye drops, inhalers, and herbal products you use, especially medicines that slow the heart or lower blood pressure. Grapefruit juice may make side effects more likely.
Many people tolerate diltiazem without major difficulty. The most reported effects are headache, flushing, dizziness, tiredness, nausea, constipation, ankle swelling, and a slower pulse.
Ankle swelling can be frustrating. It is caused by altered pressure within small blood vessels rather than simple fluid retention, so increasing water tablets without medical advice is not an appropriate fix.
Seek urgent medical assessment for:
Constipation is often overlooked until it becomes persistent. Adequate fluid intake, dietary fibre, and regular movement can help, unless a clinician has advised fluid restriction for heart failure or kidney disease.
The most avoidable problems arise from administration errors or unrecognised interactions.
Some people measure blood pressure immediately after exercise, a hot bath, caffeine, or a stressful journey. Those readings can be misleading. Sit quietly for several minutes, keep both feet on the floor, and record readings at similar times on different days.
In clinical practice, prescribers often value diltiazem when one medicine can address both blood-vessel tone and an elevated heart rate. A good response is usually measured through home blood-pressure readings, resting pulse, symptom frequency, and tolerance rather than a single reading in clinic.
Doctors also pay close attention to fatigue and ankle swelling. These effects are common reasons for reviewing the regimen, especially when they interfere with walking, work, or sleep. A low pulse may be acceptable in a physically fit person without symptoms, but the same number can be concerning when it comes with dizziness or fainting.
Consistency matters because blood-pressure and angina control depend on stable drug exposure.
Diltiazem begins affecting heart rate and blood vessels after doses are absorbed, though the practical benefit for blood-pressure control is assessed over repeated readings. Angina prevention also depends on regular dosing rather than a single capsule. NHS guidance reviewed in 2025 advises ongoing use as prescribed even when a person feels well. A prescriber may adjust treatment after reviewing pulse, symptoms, and blood-pressure trends. Keeping a symptom diary can help make that review more useful.
Food instructions depend on the prescribed capsule formulation, so the regimen should remain consistent from day to day. Taking a capsule with breakfast every day is different from alternating between fasting and fed doses. The MHRA’s 2024 medicines safety guidance supports consistent administration where modified-release medicines are involved. Grapefruit and grapefruit juice should be avoided because they may increase diltiazem exposure.
Yes, ankle swelling is a recognised calcium-channel-blocker effect. It may be mild and more visible in the evening after standing or sitting for long periods. NICE hypertension guidance updated in 2023 includes calcium-channel blockers among treatment options where tolerability should guide medicine choice. Sudden swelling with breathlessness, chest pain, or rapid weight change needs urgent assessment.
The combination can be used in selected patients, but it needs clinical supervision because both medicines can slow the heart and reduce blood pressure. Symptoms such as faintness, unusual tiredness, or a resting pulse that is much slower than usual should be assessed promptly. The British National Formulary, updated in 2025, lists the combination as one requiring caution because of bradycardia and atrioventricular block risk. Do not start or stop either medicine independently.
Blood pressure, angina frequency, or fast heart-rate symptoms can return when diltiazem is withdrawn suddenly. The risk is greater when the medicine was controlling frequent angina or an arrhythmia. NHS advice from 2025 recommends discussing treatment changes with the prescriber before stopping. A gradual change may be used where clinically appropriate.
Diltiazem requires individual assessment in pregnancy because maternal cardiovascular benefit must be balanced against fetal considerations. It can pass into breast milk, so breastfeeding decisions also need a prescriber-led review. The UK Teratology Information Service updated its cardiovascular-medicine information in 2024 to support individualised risk assessment for medicines used in pregnancy. A person who becomes pregnant while taking diltiazem should arrange a timely medication review rather than stopping abruptly.
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