Verapamil

Key facts

• Verapamil (found in brands such as Isoptin) is a calcium-channel blocker used for high blood pressure, angina, and fast or irregular heart rhythms such as supraventricular tachycardia; it is also used off-label to prevent cluster headache.
• It is taken as tablets, once or twice daily depending on whether you have an immediate-release or extended-release formulation.
• Verapamil slows electrical conduction through the heart. Combining it with a beta-blocker, or with other drugs that slow heart conduction, can cause severe bradycardia or heart block, so this combination should be avoided unless a specialist directs otherwise.
• Seek urgent care for a very slow or irregular pulse, fainting, or sudden breathlessness with swelling.

What verapamil treats

Verapamil treats hypertension, angina caused by reduced blood flow to the heart, and supraventricular arrhythmias, including atrial fibrillation needing rate control. It is also prescribed off-label to prevent cluster headache. It is not suitable for people with heart failure with reduced pumping function, because it can weaken the heart's contraction further.

How verapamil works

Verapamil blocks calcium from entering the muscle cells of the heart and blood vessels. With less calcium entering, the heart's electrical conduction slows and its contractions weaken slightly, while blood vessels relax and widen. Together these effects lower blood pressure, ease the heart's workload, and steady an overly fast or irregular rhythm.

Before you take it

• Avoid verapamil if you have severe heart failure, sick sinus syndrome or heart block without a pacemaker, or very low blood pressure.
• Do not combine verapamil with a beta-blocker or other AV-node-blocking drugs unless a specialist has assessed the risk of severe bradycardia or heart block.
• Tell your prescriber about digoxin, statins such as simvastatin, and any other heart medicines; verapamil can raise their levels.
• Grapefruit juice can raise verapamil levels in your blood; check with your pharmacist if you drink it regularly.

Side effects

Common effects include constipation, headache, flushing, dizziness on standing, and swelling of the ankles.

Stop and seek urgent medical care for any of these:

• A very slow, irregular, or pounding heartbeat.
• Fainting or severe dizziness.
• Sudden breathlessness, rapid weight gain, or worsening swelling, which can signal heart failure.
• Severe or persistent constipation.

Safety essentials

• Never combine verapamil with a beta-blocker or other heart-rate-slowing medicine without specialist supervision. Together they can cause severe bradycardia or complete heart block.
• Constipation is common and can become significant; increase fluids and fiber, and tell your prescriber if it persists.
• Do not stop verapamil suddenly; your prescriber will advise on tapering if treatment changes.
• Have your blood pressure and pulse checked regularly, especially after starting or changing the dose.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.