GTN Spray is used to treat and prevent heart-related chest pain (angina). Angina occurs when the heart muscle is not getting enough blood. This medicine works by relaxing and widening blood vessels so blood can flow more easily to the heart. It has a very short-lived effect. GTN Spray should be taken at the first sign of chest pain. It should be used in the dose and duration as advised by your doctor. Seek medical help immediately if your chest pain continues for more than 15 minutes. Some people may be advised to use this medicine prior to any exertional activity or exercise, which may precipitate angina. The most common side effect of this medicine is a headache which may be severe. This can sometimes be helped by drinking plenty of fluids and avoiding alcohol. You may also experience lightheadedness, which could increase your risk of having a fall. Do not use this medicine if you are taking medicines to treat high blood pressure in your lungs (pulmonary hypertension), or erectile dysfunction; or if you have anemia or glaucoma (increased pressure inside the eye). Always tell your doctor what other health conditions you have and what other medicines you are taking. It is best not to drink alcohol with this medicine as it increases some of the side effects. If you are affected by dizziness, avoid driving. If you are pregnant, thinking about becoming pregnant, or breastfeeding, ask your doctor before taking this medicine.