Dipyridamole: preventing stroke and clots, capsules or tablets

Dipyridamole slows the blood's clotting action by making platelets less sticky. That helps prevent unwanted clots forming in narrowed blood vessels, which lowers the risk of heart attack and stroke. The NHS links it to stroke and TIA prevention and to preventing clots after heart valve replacement surgery.

Most adults aged 18 and over can take it. Children may be prescribed it for Kawasaki disease or to prevent clots after heart surgery, with weight-based doses taken two to three times a day.

Slow-release capsules are usually 200mg, taken twice a day: one in the morning and one in the evening, with or soon after a meal. Swallow them whole and do not crush or chew them. They are not for children.

Tablets and liquid are typically taken as 300mg to 600mg a day split into 3 or 4 smaller doses, before meals and at the same times each day. Swallow tablets whole and measure liquid with a syringe or measuring spoon, not a kitchen teaspoon.

The NHS lists several reasons dipyridamole may be unsuitable: an earlier allergic reaction, angina or other heart conditions including a recent heart attack, myasthenia gravis, bleeding disorders such as haemophilia or von Willebrand disease, low blood pressure, migraines, and being pregnant, trying for a baby or breastfeeding.

Say so if any of these apply. The prescriber may choose another medicine or monitor you more closely.

Common effects include nausea or vomiting, diarrhoea, headaches and dizziness. Taking tablets with or after food helps nausea, headaches may respond to rest, fluids and cutting down alcohol, and rising slowly from a chair helps with dizziness. Do not drive or use machinery if you feel dizzy or shaky.

Rarely, it can cause easy bruising or prolonged bleeding, which merits a call to NHS 111, and chest pain, breathlessness or a rapid heartbeat or signs of anaphylaxis, which need 999.

Other clot-preventing medicines such as low-dose aspirin, clopidogrel, ticagrelor, warfarin, dabigatran, apixaban and rivaroxaban affect the bleeding risk and your prescriber should know about them. Blood pressure medicines such as bisoprolol, ramipril and furosemide can add to dizziness.

Indigestion remedies including famotidine, omeprazole and antacids with magnesium or aluminium may reduce the effect of the tablets and liquid, so the NHS suggests separating them by 2 to 3 hours. Avoid 300mg aspirin and ibuprofen unless advised, but paracetamol can be used. Ginkgo and other herbal products need caution.

You can drink alcohol, but both alcohol and dipyridamole lower blood pressure, so dizziness is possible; the NHS suggests no more than 14 units a week. It is not often used in pregnancy because of limited safety data, but a doctor may recommend it if the benefits outweigh the risks. It may be possible while breastfeeding if the baby is healthy. There is no evidence it affects fertility.

You will usually need to take it for life. Do not stop without speaking to your doctor, because clotting returns to normal within 2 days. For a missed dose, take it when remembered unless the next is close, and never double up. If you take too much and have chest pain, a rapid heartbeat or dizziness, call 999.