Glyceryl trinitrate, or GTN, is a type of medicine called a nitrate. It is used to treat angina (chest pain).

It can help stop chest pain if an angina attack has already started. It can also help to prevent them from starting.

GTN ointment can also be used to treat tears in the skin around your bottom (anal fissures).

It comes as tablets or as a spray that you put under your tongue. It also comes as patches and ointment that you put on your skin.

Sometimes GTN patches are used in hospital to make your veins easier to see if you need to have a drip (infusion).

GTN is available on prescription.

• GTN skin patches or ointment are used every day to help prevent chest pain starting.
• You use the tablets or spray during an angina attack, or before any activity that's likely to cause an attack.
• The most common side effects are headaches, feeling dizzy, weak, tired or sick (nausea), and flushing.
• Usually you will use GTN for a long time, possibly for the rest of your life.

GTN can only be used by adults aged 18 years and above. Do not give it to children.

This medicine is not suitable for some people. Tell your doctor or pharmacist if you have:

• ever had an allergic reaction to GTN or any other medicine in the past
• any recent brain or head injuries or problems (including bleeding in your brain and raised pressure in your head)
• ever had a stroke
• any heart problems (other than angina), including a recent heart attack or heart failure
• low blood pressure (hypotension)
• anaemia
• glaucoma

Take GTN exactly as your doctor or pharmacist tells you to. Always follow the instructions that come with the medicine.

How much GTN you take depends on how bad your angina is and whether you have tablets, spray, patches or ointment.

Sometimes patches are not enough to prevent all your angina attacks. Your doctor may give you GTN tablets as well.

Stopping chest pain during an angina attack

GTN tablets and spray are used under your tongue. The medicine is absorbed into your body very quickly this way, so it can be used for fast relief of chest pain caused by angina.

It's a good idea to learn how to take your GTN tablets and spray as soon as you get them. You might need to use them in a hurry if you get an angina attack.

Keep your tablets or spray with you all the time, so you can use them if you get chest pain.

Tablets – 1 tablet under your tongue as soon as possible. If you're still in pain after 5 minutes you can have a second dose by putting 1 more tablet under your tongue. If you're still in pain after 5 minutes you can have a third and final dose.

Spray – 1 or 2 sprays under your tongue. If you're still in pain after 5 minutes you can have a second dose of 1 or 2 sprays under your tongue. If you're still in pain after 5 minutes you can have a third and final dose.

Do not use more than 3 doses during an angina attack. 1 dose is either 1 tablet or 1 to 2 sprays.

Preventing chest pain before exercise or physical effort

Tablets – put 1 tablet under your tongue before you start your activity. The tablets usually take 1 to 3 minutes to work.

Spray – use 1 or 2 sprays under your tongue before you start your activity. The spray usually takes 1 to 3 minutes to work.

Preventing angina with a daily patch or ointment

Patches – usually you put on 1 patch in the morning and take it off before you go to bed at night. Each morning you put on a new patch. It's best to have 8 to 12 hours without a patch. Otherwise the GTN can stop working over time.

Usually 1 patch a day is enough. If this does not work, your doctor might increase your dose, or tell you to keep the patch on for longer.

Do not stop using the patches suddenly, without talking to your doctor first.

Ointment – your dose depends on how much GTN you can tolerate before getting a headache. Gradually increase the amount you use until you find the right dose for you.

On the first day, use just over 1cm (half an inch) in the morning. You can use another 1cm every 3 or 4 hours if you need to. On the 2nd day, use 2cm in the morning. You can use another 2cm every 3 to 4 hours. Increase your dose by 1cm each day, until the ointment gives you a headache.

Your usual dose will be 1cm less than the dose that gave you a headache. The usual dose is between 2cm and 5cm (1 to 2 inches) of ointment, repeated every 3 to 4 hours if you need it.

If you need to use the ointment several times a day, your doctor may change your dose.

How to take GTN tablets

1. Sit down.
2. Put a tablet under your tongue and close your mouth.
3. Allow the tablet to dissolve slowly – do not suck, chew or swallow it.
4. Close the container – this is important, so your tablets do not lose their strength.
5. Rest for a while, then stand up slowly.

It's a good idea to have a spare, unopened bottle of tablets. It's important to not run out.

How to use GTN spray

Before using the spray for the first time, check it's working by pressing the button on the nozzle at the top of the bottle a few times, until a fine mist comes out. Do a test spray onto a tissue so you know how it works.

1. Sit down.
2. If you have not used your spray for over a week, do 1 spray into the air before you use it.
3. Hold the nozzle in front of your mouth, with your finger on the button, and take a deep breath.
4. Open your mouth and lift your tongue up.
5. Spray the GTN under your tongue by pressing once firmly – do not breathe in while you spray.
6. Close your mouth immediately.
7. Breathe through your nose keeping your mouth closed.
8. Rest for a while before you stand up slowly.

It's a good idea to have a spare spray. It's difficult to tell how much is left in a bottle and it's important to not run out.

How to apply a GTN patch

1. Sit down.
2. Decide where to put your patch – choose an area of skin with no hair, or very little hair, so the patch sticks well. Good places are the side of your chest, upper arm, shoulder or thigh. Put your patches in a different place each day of the week, and wait several days before using the same place again.
3. Wash the area of skin and dry it completely – do not use talcum powder or anything else on your skin.
4. Open the GTN packet with your fingers – do not use scissors because you might cut the patch.
5. Remove the patch from the packet. Peel the plastic backing off the patch and throw it away – do not touch the sticky surface of the patch with your fingers.
6. Put the sticky side of the patch on the clean skin – press it down firmly and count to 5.
7. Rub your finger round the edge of the patch to make sure no air or water can get in.

If you have put your patch on properly, you can have a warm (not too hot) bath or shower, or go swimming while the patch is on.

How to apply ointment

1. Sit down.
2. Measure the dose – squeeze the right length of ointment onto the paper measure that comes in the packet.
3. Apply the ointment to your skin by holding the paper and pressing the ointment on to your chest, thigh, or arm until it is spread in a thin layer under the paper. Do not rub the ointment in. You can use surgical tape to stick the paper onto your skin.

If you have been prescribed ointment for an anal fissure, ask your doctor about the best way to apply it.

Will my dose go up or down?

You may need to reduce your dose if you get too many side effects or if you start taking other medicines. Your doctor will discuss this with you.

You may need a stronger dose if GTN stops working as well as it used to. This sometimes happens. Tell your doctor if you notice that GTN is not working as well as usual.

What if I forget to take it?

If you forget to use your GTN before exercise, or another activity that could cause an angina attack, take it as soon as you remember. Do not restart the exercise or activity until the GTN has had the usual time to work.

If you forget to put your daily patch on at the usual time, put a new patch on as soon as you remember, unless it's nearly time for your next patch. In this case, just skip the missed patch and apply the next one at the usual time.

If you miss a dose of your daily ointment, use it as soon as possible, unless it's nearly time for your next dose. In this case, just leave out the missed dose and apply the next one as usual.

Never use a double dose to make up for a forgotten dose.

If you often forget doses, it may help to set an alarm or reminder to help you remember. You can ask a pharmacist for advice on other ways to help you to remember to use your medicine.

What if I take too much?

If you use too much GTN spray, sit down and put your feet up if you feel faint. If you take too many tablets, remove any tablets that are left undissolved in your mouth. If you use too much ointment, wash it off. If you use too many patches, remove them.

You might get side effects such as headaches, a fast heartbeat or feeling dizzy. However, you probably will not need medical treatment. Contact your doctor if your symptoms do not get better.

If you need to go to A&E, do not drive yourself – get someone else to drive you or call an ambulance.

Take any leftover GTN tablets, spray, patches, or ointment, and the packet or leaflet with you.

Like all medicines, GTN can cause side effects, although not everybody gets them. Side effects often improve as your body gets used to the medicine.

Common side effects

These common side effects happen in more than 1 in 100 people, but some are less likely if you're using skin patches.

Talk to your doctor or pharmacist if these side effects bother you or last more than a few days:

• headaches (very common)
• feeling dizzy
• feeling weak, tired or sleepy
• feeling sick (nausea)
• red face (flushing)

Serious side effects

Serious side effects after taking GTN are rare and happen in less than 1 in 1,000 people.

Serious allergic reaction

In rare cases, it is possible to have a serious allergic reaction (anaphylaxis) to GTN.

These are not all the side effects of GTN. For a full list see the leaflet inside your medicines packet.

What to do about:

• headaches – make sure you rest and drink plenty of fluids. Ask a pharmacist to recommend a painkiller for headaches. Paracetamol is safe to take with GTN. Try to avoid alcohol, as it could make your headaches worse. Headaches usually go away after a few days if you use GTN regularly. Talk to your doctor if they last longer than a week or are severe. If using GTN ointment, reduce your ointment by 1cm if you are trying to find the right dose.
• feeling dizzy, weak, tired or sleepy – stop what you are doing and sit or lie down until you feel better. Avoid alcohol, as it could make you feel worse. Do not drive, ride a bike or use tools or machinery until you feel better.
• feeling sick – this usually goes away on its own, but it might help to take sips of a cold drink (fizzy drinks help some people), or peppermint tea. This will also stop you getting dehydrated. Avoid rich, greasy or spicy foods, as these could make you feel worse. Stick to small, simple snacks or meals if you are hungry.
• red face (flushing) – try to cut down on coffee, tea and alcohol because they can make flushing worse. It might help to keep the room cool and use a fan. You could also spray your face with cool water or sip cold or iced drinks. The flushing should go away after a couple of hours if you have used GTN only once, or after a few days if you use GTN every day.

Talk to your doctor about the benefits and risks of using GTN while you’re pregnant.

Talk to your doctor if you’re trying for a baby or you’re already pregnant.

GTN and breastfeeding

If you are breastfeeding, talk to your doctor or pharmacist about using GTN.

There's not enough research into whether GTN passes into breast milk. If your doctor and health visitor say your baby is healthy, GTN could be used during breastfeeding.

If your doctor decides that you need to take GTN it is important that you keep taking it to keep you well. Breastfeeding will also benefit both you and your baby.

If you do breastfeed while taking GTN, look out for the side effects in your baby. If you notice that your baby is not feeding as well as usual, or seems unusually sleepy, or if you have any other concerns about your baby, talk to your health visitor or doctor.

Some medicines can interfere with the way GTN works.

If you take other medicines that lower blood pressure with GTN, it can sometimes lower your blood pressure too much. This might make you feel dizzy or faint.

Tell your doctor if this happens to you – they may need to change your dose.

Check with a pharmacist or your doctor if you're taking:

• medicines for erection problems such as alprostadil, avanafil, sildenafil (Viagra), tadalafil (Cialis), vardenafil
• anticoagulant medicine such as heparin
• medicines for depression or other mental health conditions
• medicines for high blood pressure or heart problems
• medicines for migraine that contain ergot alkaloids or ergotamine such as Migril
• medicine for Parkinson's disease such as apomorphine

If you take GTN tablets, tell a doctor or pharmacist if you take any medicines that make your mouth dry (including some antidepressants, cold medicines or medicines for urinary incontinence). This is because a dry mouth can reduce how well GTN tablets work, so GTN spray may be better for you.

Taking GTN with painkillers

Paracetamol is safe to take with GTN.

Do not take non-steroidal anti-inflammatory medicines (NSAIDs) regularly, such as aspirin, ibuprofen and naproxen. These may make your angina worse.

Talk to your pharmacist if you need a painkiller stronger than paracetamol.