Glyceryl trinitrate

What it is

Glyceryl trinitrate is a nitrate that the body converts to nitric oxide, which relaxes the smooth muscle in blood vessel walls. The resulting widening of veins and arteries reduces the work the heart has to do and improves blood supply to the heart muscle. It is used for angina pectoris, both to relieve an attack and to cover exertion that is known to bring one on.

Used for

• Angina pectoris

What to know while taking it

Because it dilates vessels throughout the body, it commonly lowers blood pressure and often causes a throbbing headache, especially in the first days of use; sitting or lying down when taking it reduces the risk of feeling faint. It must not be combined with erectile-dysfunction drugs such as sildenafil or tadalafil, as the two together can cause a sudden and dangerous drop in blood pressure. Alcohol and hot weather add to the same blood-pressure effect.

When to see a doctor

Chest pain that does not settle after three doses is a medical emergency and needs an ambulance, not another dose. Fainting, a pounding heartbeat, or headaches that do not ease with continued use are reasons to see a doctor.

Worth knowing

• Can lower blood pressure
• Headache is a common effect
• No relief after three doses is an emergency