Verapamil: uses, doses, side effects and cautions

Verapamil treats irregular heart rhythms (arrhythmias) and high blood pressure, and helps prevent heart disease, heart attacks and stroke in people with high blood pressure. It prevents angina chest pain, and specialists prescribe it for cluster headaches.

It relaxes and widens blood vessels, which lowers blood pressure and improves the blood and oxygen supply to the heart, and it relaxes the heart and slows the heart rate, which helps heart rhythm problems. It is prescription only.

The NHS gives these usual adult doses. Your prescriber decides your own dose.

Most adults and children aged 1 year and over can take verapamil. Tell the prescriber if you have had an allergic reaction to it, have liver or kidney problems, low blood pressure, porphyria, heart failure, a very slow or irregular heart rate, Wolff-Parkinson-White syndrome, a muscle disorder such as myasthenia gravis, Lambert-Eaton myasthenic syndrome or muscular dystrophy, or if you are pregnant, trying to conceive or breastfeeding.

Swallow tablets whole with a drink of water; do not chew or crush them. Take it at the same time daily, with or without food. Treatment is usually long term and can be for the rest of your life.

If you miss a dose, take it promptly unless the next is near, in which case skip it. Never double up. Call NHS 111 if you take too much; symptoms include low blood pressure, fainting, dizziness and an irregular heartbeat. Talk to your doctor before stopping, because stopping may make blood pressure rise and increase the risk of a heart attack or stroke.

Constipation: eat more fibre such as fruit, vegetables and cereals and drink plenty of water. For nausea, eat simple food and take verapamil after a meal or snack. For flushing, cut down on coffee and tea and keep the room cool. Headaches: rest, drink fluids, and paracetamol is safe. If dizzy, sit or lie down until it passes, and do not drive or use machinery.

Call NHS 111 or a doctor for yellow eyes or skin, dark urine or swelling of hands, feet, ankles or legs. Call 999 for chest pain that does not ease after several minutes with sweating, nausea or breathlessness, and for signs of anaphylaxis. Avoid alcohol if it worsens symptoms.

Named medicines include the antibiotics clarithromycin, erythromycin and rifampicin, itraconazole, digoxin, ivabradine, flecainide, quinidine, dabigatran, darunavir, ritonavir, carbamazepine, phenytoin, ciclosporin, tacrolimus, simvastatin, atorvastatin and colchicine.

Paracetamol is the best painkiller, with ibuprofen as an alternative if it does not work. St John's wort can affect how verapamil works, and grapefruit can make side effects worse.

You may take verapamil during pregnancy, though it is not often prescribed; people taking it for high blood pressure usually switch, and those taking it for angina or rhythm problems should consult an obstetrician and cardiologist first. It passes into breast milk in tiny amounts and has not been known to cause side effects in breastfed babies. The NHS found no evidence that it reduces fertility. Report suspected side effects via the Yellow Card scheme.