Isosorbide mononitrate

Key points about isosorbide mononitrate

  • Isosorbide mononitrate is used to prevent chest pain (also called angina).
  • Isosorbide mononitrate is also called Ismo 20®, Ismo 40 Retard®, and Duride®.
  • Find out how to take it safely and possible side effects.
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Isosorbide mononitrate is used to prevent chest pain (also called angina). Angina happens when the blood supply to the muscles of your heart are restricted, due to narrowing of the blood vessels supplying the heart.

Isosorbide mononitrate works by widening blood vessels, letting more blood and oxygen reach the heart which reduces strain on your heart, making it easier for the heart to pump blood.

NOTE: isosorbide mononitrate will not treat chest pain (an angina attack) that has already started. Your doctor will give you a spray (GTN spray) to use if you have an attack of angina. Read more about angina and GTN spray

Isosorbide mononitrate is also sometimes used together with other medicines for people with heart failure. This is a condition where there is a problem with the pumping action of the heart. Read more about heart failure.

In New Zealand isosorbide mononitrate is available as immediate-release tablets (20 mg) and slow release tablets (40 mg and 60 mg).

  • The dose of isosorbide mononitrate will be different for different people, depending on what it is being used for.
  • Your doctor will usually start you on a low dose and increase the dose depending on how you respond. This allows your body to get used to the medicine and reduces side effects.
  • Always take your isosorbide mononitrate exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much to take, how often to take it and any special instructions.
  • Isosorbide mononitrate tablets are available in different strengths. If your tablets look different to your last supply speak with your doctor or pharmacist for advice.

Isosorbide mononitrate tablets are available in 2 forms: immediate release tablets and slow release tablets.

 Formulation  How to take it
Immediate release tablets (20 mg)
  • These are taken two or three times a day.
  • Try to space your doses evenly throughout the day.
  • Do not crush or chew the tablets.
Slow release tablets (40 mg and 60 mg)
  • These are taken once a day, in the morning.
  • Do not crush or chew the tablets.
  • The 60 mg Duride® tablets may be broken in half but not the 40 mg ISMO 40 Retard®.
    If you are unsure about whether your tablets can be halved, ask your pharmacist.
  • Swallow your tablets with a glass of water.  
  • You can take isosorbide mononitrate with or without food.
  • Limit alcohol intake while you are taking isosorbide mononitrate. Alcohol can increase your chance of side effects, such as dizziness and light-headedness.
  • If you forget to take your dose, take it as soon as you remember. But, if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
  • Do not stop taking isosorbide mononitrate suddenly – this can make your angina worse.
If your angina becomes more frequent or severe, lasts longer or happens when you are doing very little or resting, see your doctor.  

  • Are you pregnant, planning a pregnancy or breastfeeding?
  • Do you have problems with your kidneys or liver?
  • Do you have heart failure or have you recently had a heart attack?
  • Do you have glaucoma?
  • Do you have an underactive thyroid (hypothyroidism)?
  • Are you are taking or using any other medicines? This includes any medicines you are using that are available to buy from a pharmacy, supermarket or natural health store without a prescription. It is particularly important that you tell your doctor or pharmacist if you are using any medicines to help treat erectile dysfunction.

If so, it’s important that you tell your doctor or pharmacist before you start taking isosorbide mononitrate. Sometimes a medicine isn’t suitable for a person with certain conditions or it can only be used with extra care.

Do not take isosorbide mononitrate if you are taking medicines used to treat erection problems, such as:
  • sildenafil (Viagra, Avigra, Vedafil, Silvasta)
  • tadalafil (Cialis)
  • vardenafil (Levitra).

Using erectile dysfunction medicine with isosorbide mononitrate can cause a sudden decrease in blood pressure, which can be life-threatening. 

Like all medicines, isosorbide mononitrate can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Headache
  • This is quite common when you first start taking isosorbide mononitrate and should settle after a few days.
  • Tell your doctor if it is ongoing 
  • Dizziness
  • Feeling lightheaded
  • Feeling faint when you stand up
  • This is quite common when you first start taking isosorbide mononitrate and usually goes away with time.
  • Be careful when getting up from either lying down or sitting to avoid falls. These effects put you at risk of falls and injuries, especially if you are an older adult.
  • Stand up slowly. If you do feel dizzy sit or lie down for a few moments.
  • Avoid alcohol.
  • Tell your doctor if this continues.
  • Tiredness, blue lips, problems breathing, fainting
  • Tell your doctor immediately or ring HealthLine 0800 611 116.
  • Changes in your heart beat (either fast, slow or irregular)
  • Tell your doctor.
  • Signs of an allergic reaction such as skin rash, itching, swelling of your lips, face and mouth or difficulty breathing, such as chest tightness or wheezing
  • Tell your doctor immediately or ring HealthLine 0800 611 116.
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product(external link)

  • Isosorbide mononitrate may interact with a few medications and herbal supplements so check with your doctor or pharmacist before starting isosorbide mononitrate or before starting any new medicines.
  • Isosorbide mononitrate interacts with medicines to treat erectile problems such as sildenafil (Viagra, Avigra, Vedafil, Silvasta), tadalafil (Cialis) and vardenafil (Levitra).

The following links have more information on isosorbide mononitrate.

Isosorbide mononitrate(external link) New Zealand Formulary Patient Information


Isosorbide mononitrate in Te Reo Māori(external link)(external link) My Medicines, NZ, 2018
5 questions to ask about your medications(external link) Health Quality and Safety Commission, NZ, 2019 English(external link), te reo Māori(external link)


  1. Isosorbide mononitrate(external link) New Zealand Formulary

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Credits: Sandra Ponen, Pharmacist. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Angela Lambie, Pharmacist, Auckland

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