1. About glyceryl trinitrate (GTN)
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.
2. Key facts
- 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.
3. Who can and cannot take it
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)
4. How and when to take or use it
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.
Immediate action required: Call 999 if:
You have taken 3 doses of GTN and:
- you're still in pain 5 minutes after your 3rd dose or your pain is getting worse
- you feel unwell
These are signs that you may be having a heart attack.
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
- Sit down.
- Put a tablet under your tongue and close your mouth.
- Allow the tablet to dissolve slowly – do not suck, chew or swallow it.
- Close the container – this is important, so your tablets do not lose their strength.
- 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.
- Sit down.
- If you have not used your spray for over a week, do 1 spray into the air before you use it.
- Hold the nozzle in front of your mouth, with your finger on the button, and take a deep breath.
- Open your mouth and lift your tongue up.
- Spray the GTN under your tongue by pressing once firmly – do not breathe in while you spray.
- Close your mouth immediately.
- Breathe through your nose keeping your mouth closed.
- 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
- Sit down.
- 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.
- Wash the area of skin and dry it completely – do not use talcum powder or anything else on your skin.
- Open the GTN packet with your fingers – do not use scissors because you might cut the patch.
- 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.
- Put the sticky side of the patch on the clean skin – press it down firmly and count to 5.
- 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
- Sit down.
- Measure the dose – squeeze the right length of ointment onto the paper measure that comes in the packet.
- 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.
Immediate action required: Call 999 if:
- your mouth (lips, tongue or gums), face or skin start to look blue or grey.
Urgent advice: Call 111 now if:
- you take too many GTN tablets, use too many patches, or too much ointment, and you feel unwell
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.
5. Side effects
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.
Immediate action required: Call 999 or go to A&E now if:
- you are having breathing difficulties that are new or worse than usual
- you get weakness in 1 arm or leg, or 1 side of your body or face, difficulty speaking, or loss of coordination – this could be signs of a stroke
- your lips, tongue, face or skin suddenly turn blue or grey, or if you have darker skin and your gums and round the eyes turn blue or grey – these are signs of a problem with the oxygen levels in your blood
- your heart starts beating much faster or slower than usual
- you get chest pain that is different or worse than your usual angina pain
- you have fainted (lose consciousness)
- you go blind in 1 eye
Serious allergic reaction
In rare cases, it is possible to have a serious allergic reaction (anaphylaxis) to GTN.
Immediate action required: Call 999 or go to A&E now if:
- you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
- you're wheezing
- you get tightness in the chest or throat
- you have trouble breathing or talking
- your mouth, face, lips, tongue or throat start swelling
These are warning signs of a serious allergic reaction and may need immediate treatment in hospital.
These are not all the side effects of GTN. For a full list see the leaflet inside your medicines packet.
You can report any suspected side effect to the UK safety scheme.
6. How to cope with side effects
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.
7. Pregnancy and breastfeeding
GTN and pregnancy
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.
Non-urgent advice: Talk to your doctor or pharmacist if you're:
- trying to get pregnant
8. Cautions with other medicines
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 ibuprofen, aspirin and naproxen. These may make your angina worse.
Talk to your pharmacist if you need a painkiller stronger than paracetamol.
Important: Medicine safety
Tell your doctor or pharmacist if you're taking any other medicines, including herbal medicines, vitamins or supplements.
9. Common questions
How does it work?
Glyceryl trinitrate, or GTN, is a type of medicine called a nitrate. Nitrates are used to treat angina.
Angina is chest pain that happens when not enough blood gets to the muscles of the heart. It usually happens because your arteries have become hardened and narrowed.
Your heart muscles need the oxygen in blood to work. If your heart needs to work harder, during exercise for example, it needs increased blood flow to get more oxygen.
In angina, GTN works by widening blood vessels (veins and arteries). This increases the blood supply to your heart, which gets more oxygen to your heart muscles and this reduces chest pain.
By widening blood vessels GTN also makes it easier for your heart to pump blood around your body, so your heart muscles get more oxygen, reducing the risk of getting chest pain.
How long will I take or use it for?
Usually you will use GTN for a long time, possibly for the rest of your life.
Do GTN tablets go out of date?
GTN tablets go out of date (expire) 8 weeks after the bottle is opened. This is because the active ingredient can evaporate, which means the tablets will not work properly after that time.
To make sure your tablets do not lose their strength before 8 weeks you need to:
- keep them in the bottle they came in
- close the lid tightly after you have taken each tablet out
- do not put anything else inside your tablet bottle
Make sure you have a new supply of GTN to use after each pack expires. Always check the expiry date on the pack.
After 8 weeks, if you have any tablets left in the bottle, return that bottle to a pharmacy so they can dispose of it in the right way.
Can I take it for a long time?
There are no issues with taking GTN for a long time. Most people can take it with no problems.
What will happen if I stop taking it?
Talk to your doctor if you want to stop taking GTN.
If you have been using GTN regularly and you stop taking it, your angina may get worse. This may increase your risk of a heart attack or stroke.
If you are taking GTN and are bothered by side effects, speak to your doctor. They may be able to change your dose or prescribe a different medicine instead.
Are there other medicines for angina?
GTN is the only medicine available for fast relief of angina symptoms and to prevent pain before exercise or physical effort.
There are other medicines that can be taken regularly to prevent angina attacks, including:
- long-acting nitrates, such as isosorbide mononitrate
- beta-blockers such as atenolol
- calcium channel blockers, such as verapamil or diltiazem
- medicines such as ranolazine, nicorandil or ivabradine
Your doctor will decide which is the best medicine for you.
Will I need to stop taking it before surgery or before tests?
If you're having surgery, you need to let the doctors know that you use GTN. They might ask you to stop using GTN for a short time before surgery.
This is because some of the medicines used to make you sleep and not feel pain during surgery (anaesthetic) can make the side effects of GTN worse.
You must tell the doctor or nurse if you are wearing a GTN patch if you are going to have certain types of tests and treatments including:
- an MRI scan
- diathermy treatment (treatment using hot wires)
- electrical treatment on your heart
Can I drink alcohol with it?
Alcohol increases the blood pressure lowering effect of GTN, so it can make you feel dizzy, faint or sleepy.
If this happens to you, it's best if you do not drink alcohol while you're taking GTN. If this does not happen to you, it's still better to not drink too much alcohol while you're taking GTN.
Is there any food or drink I need to avoid?
You can eat normally while you are using GTN, but angina is a warning sign that you are at risk of serious problems such as heart attacks and strokes.
You can help reduce your risk of problems like these by:
- eating a balanced diet
- cutting down on alcohol
- losing weight if you are overweight
Will it affect my contraception?
GTN will not stop your contraception working.
If you have angina, oral contraceptives are not recommended because they increase the risk of heart attack and stroke.
Will it affect my fertility?
There is no firm evidence that GTN affects fertility in men or women. If you are trying to get pregnant, talk to your doctor about using GTN.
Will it affect my sex life?
Some people with angina worry that having sex will trigger an angina attack, but the risk of this happening is low. It is as safe as other forms of exercise with similar levels of effort.
If you are worried about having an angina attack during sex:
- keep your GTN nearby, so you can use it quickly if you need to
- think about taking a tablet or using your spray before you have sex, to reduce the risk of an attack
You cannot take medicines for erection problems if you are using GTN. These include:
If you have used one of these medicines, do not use or take GTN for at least 24 hours after sildenafil or vardenafil, and at least 48 hours after tadalafil.
If you have an angina attack after using one of these medicines for erection problems, stop sexual activity immediately and rest. Do not use GTN.
Immediate action required: Call 999 if:
- you still have chest pain after 10 minutes
GTN is not likely to affect your sex life in any other way.
Talk to your doctor if you are having problems with your sex life.
Do I need to avoid playing sports?
It's important to stay active if you have angina.
You might worry that exercising could trigger your symptoms or cause a heart attack, but the risk is low if you:
- build up your activity level gradually and take regular breaks
- keep your GTN tablets or spray with you in case you need them
- use your tablets or spray before starting exercise, if you need to
Talk to your doctor if you're not sure it's safe for you to exercise.
Can I drive or ride a bike?
GTN can make some people feel dizzy, sleepy or faint. If this happens to you, do not drive, ride a bike or use tools or machinery until you feel better.
Can lifestyle changes help?
Angina is a warning sign that you are at risk of serious problems such as heart attacks and strokes.
To reduce your risk of problems like these, it may help to:
- eat a healthy balanced diet – aim to eat a diet that includes plenty of fruit and vegetables, wholegrains, fat-free or low-fat dairy products, and lean proteins. This should help you to stay healthy or lose weight, which reduces your risk of heart attacks and strokes. It's a good idea to cut down on salt too.
- cut down on alcohol – drinking too much alcohol is not good for the health of your heart. Try to keep to the recommended guidelines of no more than 14 units of alcohol each week. A standard glass of wine (175ml) is 2 units. A pint of lager or beer is usually 2 to 3 units of alcohol.
- stop smoking – smoking increases your heart rate and blood pressure
- exercise – regular exercise keeps your heart and blood vessels in good condition. It does not need to be too energetic – walking every day will help. Use your GTN tablets or spray before exercise if you need to.