What is GTN sublingual tablets used for ?

How does it work ?

GTN sublingual tablets contain the active ingredient "glyceryl trinitrate", which is a type of medicine called a nitrate. It is used to help the heart work more easily. (NB. Glyceryl trinitrate is also available without a brand name, i.e. as the generic medicine.)

Glyceryl trinitrate works by being converted in the body to a chemical called nitric oxide. This chemical is made naturally by the body and has the effect of making the veins and arteries relax and widen (dilate). When the blood vessels dilate in this way there is more space inside them and hence less resistance. This makes it easier for the heart to pump blood around the body.

Widening the veins also decreases the volume of blood that returns to the heart with each heartbeat. This makes it easier for the heart to pump that blood out again.

As a result of both these actions, the heart does not need as much energy to pump the blood around the body and therefore needs less oxygen.

Glyceryl trinitrate also widens the arteries within the heart itself, which increases the blood and oxygen supply to the heart muscle.

The pain of angina is caused by too little oxygen reaching the heart when its workload increases, such as during exercise. Glyceryl trinitrate improves the oxygen supply to the heart, as well as decreasing the amount of oxygen that the heart needs by making it easier for the heart to pump blood around the body. It can therefore be used to treat angina.

GTN sublingual tablets should be allowed to dissolve under the tongue. This area of the mouth has a large supply of blood vessels that allows the medicine to be rapidly absorbed. Glyceryl trinitrate taken in this way is used to give rapid relief from the pain of an angina attack. The tablets can also be used to prevent an anticipated attack, for example before exercise or physical effort, emotional stress or exposure to cold.

Glyceryl trinitrate is also available as long-acting tablets, skin patches and ointment that are used regularly each day to help prevent angina attacks. See the factsheets linked at the end of this article for more information.

What is it used for ?

Prevention and relief of angina attacks.


Warning !

Follow the instructions you receive with this medicine. Glyceryl trinitrate sublingual tablets should be allowed to dissolve under the tongue - they should not be swallowed like normal tablets.

This medicine may cause dizziness and so may affect your ability to drive or operate machinery safely. Do not drive or operate machinery until you know how this medicine affects you and you are sure it won't affect your performance. If you do feel dizzy after taking a dose, sit or lie down until the symptoms pass.

Drinking alcohol may enhance some of the side effects of this medicine, such as feeling faint or dizzy.

Short-acting glyceryl trinitrate tablets should be kept in the container they are dispensed in and discarded after eight weeks. The tablets may lose their effectiveness if the container has been open for longer than eight weeks, or if the tablets are transferred to a different container.


Use with caution in :

- Severely decreased kidney function.

- Severely decreased liver function.

- People who have recently had a heart attack.

- Underactive thyroid gland (hypothyroidism).

- People with low levels of oxygen in their blood, eg due to lung disease.

- Dangerously low body temperature (hypothermia).

- Malnutrition.


Not to be used in :

* Allergy to nitrates.

* Low blood pressure (hypotension).

* Low volume of circulating blood (hypovolaemia).

* Inflammation of the sac surrounding the heart that stops the heart from beating properly (constrictive pericarditis).

* Fluid in the sac surrounding the heart that prevents the heart beating properly (cardiac tamponade).

* Narrowing of the main artery coming from the heart (aortic stenosis).

* Narrowing of one of the valves in the heart (mitral valve stenosis).

* Heart disease in which the muscle of the heart grows abnormally (hypertrophic obstructive cardiomyopathy).

* Head injury.

* Bleeding in the brain (cerebral haemorrhage).

* Severe anaemia.

* Closed angle glaucoma.


This medicine is not recommended for use in children.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.


Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

The safety of this medicine for use during pregnancy has not been established. It should only be used during pregnancy if the benefits to the mother outweigh any risks to the developing baby. Seek medical advice from your doctor.

It is not known if this medicine passes into breast milk. It should only be used by breastfeeding mothers if the benefits to the mother outweigh any risks to the nursing infant. Seek medical advice from your doctor.


Label warnings

Allow medication to dissolve under the tongue. Do not transfer from the original container. Keep tightly closed. Discard eight weeks after opening.


Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.


- Headache.

- Dizziness.

- Weakness.

- Nausea.

- Flushing.

- Burning or stinging sensation in the mouth.

- A drop in blood pressure that occurs when moving from a lying down or sitting position to sitting or standing, which results in dizziness and lightheadedness (postural hypotension).

- Increased heart rate (tachycardia).

- Decreased heart rate (bradycardia).

- Allergic skin reactions.

- Fainting.


The side effects listed above may not include all of the side effects reported by the drug's manufacturer.

For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.


How can this medicine affect other medicines ?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.

The medicines for erectile dysfunction (impotence) listed below must not be used by people taking glyceryl trinitrate, because the combination can produce a severe drop in blood pressure resulting in dizziness, fainting, or even a heart attack :

* sildenafil (Viagra)

* tadalafil (Cialis)

* vardenafil (Levitra).

If this medicine is taken in combination with other medicines that reduce blood pressure, either as a treatment for high blood pressure (antihypertensives), or as a side effect, there may be an enhanced blood pressure lowering effect. This might make some people feel dizzy. If you do feel dizzy, you should lie down until the symptoms pass. Other medicines that can reduce blood pressure include the following :

* ACE inhibitors, eg enalapril, captopril

* alpha blockers, eg alfuzosin, doxazosin

* alprostadil

* anaesthetics

* angiotensin II receptor antagonists, eg losartan

* certain antipsychotic medicines, eg chlorpromazine

* baclofen

* benzodiazepines, eg temazepam

* beta-blockers, eg propranolol

* calcium channel blockers, eg diltiazem, verapamil, nifedipine

* clonidine

* diuretics, eg furosemide

* hydralazine

* levodopa

* MAOI antidepressants, eg phenelzine

* methyldopa

* minoxidil

* moxisylyte

* moxonidine

* other nitrates, eg isosorbide mononitrate, amyl nitrate (poppers)

* tricyclic antidepressants, eg amitriptyline.


If you are taking medicines that can cause a dry mouth, glyceryl trinitrate sublingual tablets may be less effective because they are not able to dissolve properly under your tongue. Medicines that can cause a dry mouth include the following :


* anticholinergic medicines for Parkinson's disease, eg procyclidine, trihexyphenidyl, orphenadrine

* anticholinergic medicines for urinary incontinence, eg oxybutynin, flavoxate, tolterodine, propiverine, trospium

* antihistamines, eg brompheniramine, chlorphenamine

* antispasmodic medicines, eg hyoscine

* MAOI or tricyclic antidepressants, eg phenelzine, amitriptyline

* antipsychotic medicines, eg chlorpromazine, clozapine.

If you experience this problem, you can help the GTN tablet dissolve by drinking a mouthful of water before putting the tablet under your tongue.