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Glyceryl Trinitrate (GTN)

What is Sublingual Glyceryl Trinitrate?

Glyceryl Trinitrate tablet (GTN) is a medicine that is put under the tongue to relieve chest pain (angina) caused by lack of oxygen supply to the heart muscles.

How it acts?

It dilates blood vessels to improve blood supply to the heart. Allow the medicine to dissolve under your tongue because this area has a lot of blood vessels thus provide good absorption.

When to take?

Take GTN tablet immediately if you experience chest pain (refer to the picture below). To prevent an attack, take five minutes before you exercise, having sexual activity or prior exposure to cold.

Hot and tingling sensation under your tongue while taking this medicine proves that it is still effective.


Side effects

You may feel dizzy after taking this medicine especially when you want to stand up. Therefore, stand up slowly if you are sitting or lie down to reduce the side effect. Avoid driving or operate machinery after taking this medicine.

You may also experience headache, nausea, vomitting, fainting, difficulty in breathing, palpitations, fast or irregular heartbeat and skin allergy.

Discuss with your doctor or pharmacist if these side effects continue to bother you.

Drug interaction

Consult with your doctor or pharmacist first if you want to take GTN tablet with other herbal preparations/medicines to ensure safe combination.

You should not combine it with medicines used in the treatment of erectile dysfunction (impotence) such as sildenafil and tadalafil as these medicines can produce serious adverse events.

If you take it with other antihypertensive medicines, there may be an enhanced in the blood pressure lowering effect and increase the side effects.

However, the effect of this medicine may be reduced if you take it with medicines that can cause dry mouth such as chlorpheniramine and hyoscine as the tablet will not dissolve properly under your tongue. You can fix this by taking a mouthful of water before putting the tablet under your tongue.

Never take it with alcohol as alcohol can increase adverse effect e.g. headache.


  • Store in an amber glass bottle under room temperature, away from light, heat and humidity.

  • You must close the bottle tightly.

  • Keep in its original container.

  • Use within 8 weeks after opening.

  • Keep away from children.

  • Return the excess/expired medicines to the pharmacy to be discarded.

Getting the most from your treatment

  • Always bring along the medicine with you everywhere you go.

  • Never swallow the medicine.

  • Never stop taking unless advise otherwise by your doctor.

  • Inform your doctor or pharmacist if you experience other side effects besides mentioned those stated above pertaining to the use of this medicine.

  • Inform the person in charge that you are taking this medicine in case you have to undergo surgery or dental procedures.

  • If you are pregnant or breastfeeding, consult your doctor first before taking this medicine.

Last Reviewed : 23 April 2014
Writer : Nur Hazwani bt. Mohd Noor
Reviewer : Che Pun bt. Bujang