Consumer medicine information


50% v/v Nitrous oxide, N2O and 50% v/v Oxygen, O2

Consumer Medicine Information

What is in this leaflet

This leaflet answers some common questions about Entonox. It does not contain all the available information.

It does not take the place of talking to your doctor,, anaesthetist or appropriate healthcare professional.

All medicines have risks and benefits. Your doctor or healthcare professional has weighed the risks of you using Entonox against the benefits they expect it will have for you.

If you have any concerns about using Entonox, ask your doctor.

Keep this leaflet with you, you may want to read it again.

What Entonox is used for

Entonox is a nominal gas mixture of 50% nitrous oxide and 50% oxygen used for pain relief.

It is usually given by a doctor, anaesthetist, dentist, ambulance officer or nurse via a mask or mouthpiece in which you breathe in the gas.

Entonox works by relieving pain for certain procedures.

Your doctor may prescribe Entonox for another purpose. Ask your doctor if you have any questions about why Entonox has been prescribed for you.

This medicine is available only with a doctor’s prescription.

Before you use Entonox

When you must not use it

Do not use Entonox if:

  1. You have an allergy to Entonox or nitrous oxide or any other gas component or have had an allergic reaction in the past.
  2. You have emphysema, chronic bronchitis or if it is for a premature infant.
  3. You have a condition where air is entrapped within your body and it might expand when given nitrous oxide (eg bowel obstruction, blocked middle ear, following a recent dive). Ask your doctor for full details of these conditions.
  4. You have been using it for a prolonged period without proper monitoring of your blood.

Do not use Entonox if the cylinder is damaged or shows signs of tampering or it has degraded.

  1. You are smoking or there are naked flames nearby. You must not smoke or light any flames whilst using Entonox.
  2. You are intoxicated or heavily sedated.

Before you start to use it

You must tell your doctor if:

  1. You are allergic to any other medicines, foods, dyes or preservatives.
  2. You have had a reaction to Entonox or any other general anaesthetic or pain relief medication in the past.
  3. You have had a general anaesthetic.
  4. You have or have had any other health problems or medical conditions, including:
  • A condition known as malignant hyperthermia or a family history of it.
  • Low blood pressure
  • Low vitamin B12 levels
  • Problems with addiction to medicines
  • Bone marrow problems including various cells in the blood
  • Neurological diseases
  • Conditions in which air is entrapped within the body
  1. You are pregnant or intend to become pregnant.

Your doctor will discuss the risks and benefits of using Entonox when pregnant.

  1. You are breastfeeding or wish to breastfeed.

Your doctor will discuss the risks and benefits of using Entonox when breastfeeding.

  1. Care should be taken when using Entonox as it is stored under high pressure in gas cylinders. There are also safe working exposure levels and important storage instructions. Please discuss these with your doctor if you have any questions.
  2. You have had long term usage or been chronically exposed to nitrous oxide.
  3. You have had eye surgery within the last four weeks and a gas was used in your eye during the procedure.

Taking other medicines

Tell your doctor if you are taking any other medicines, including medicines you buy without a prescription from a pharmacy, supermarket or health food shop.

Some commonly used medicines that may interfere with Entonox include:

  • Pain relievers
  • Anaesthetics
  • Methotrexate
  • Medicines which may effect your nervous system

These medicines may be affected by Entonox or may affect how well it works. You may need to take different amounts of your medicine or you may need to take different medicines.

Some medicines may affect the way others work. Ask what to do when using Entonox with other medicines.

Your doctor may have more information on medicines to avoid while using Entonox.

If you have not told your doctor about any of the above, tell them before you start using Entonox.

How to use Entonox

Entonox should only be used under the supervision of your doctor or healthcare professional.

How much to use and how to use it

The amount of Entonox given to you will be decided by your doctor, depending on the amount of pain relief required. It is usually given to you by breathing it through a mask or mouthpiece.

If you are elderly or have lung problems, you may need a lesser amount of Entonox.

Follow all directions given to you by your doctor carefully.

These directions may differ from the information contained in this leaflet.

If you do not understand the instructions, ask your doctor for help.

How long to use it

Your doctor will decide for how long you need to use Entonox.

If you use too much (overdose)

As Entonox is most likely to be given to you under the direction of your doctor, anaesthetist, ambulance officer, dentist or nurse, it is very unlikely you will receive an overdose. However, if this happened, quick action can be taken to maintain your breathing and replace the Entonox with oxygen.

If you have any questions then ask your doctor.

After you have used Entonox

Things you must not do

Ask your doctor when it is safe for you to drive, operate machinery or perform activities following the use of Entonox.

Side effects

Tell your doctor as soon as possible if you do not feel well while you are using Entonox.

Entonox may have unwanted side effects in some people. All medicines can have side effects. Sometimes they are serious, most of the time they are not. You may need medical treatment if you get some of the side effects.

Ask your doctor any questions you may have.

Tell your doctor if you notice any of the following and they worry you:

  • Nausea, vomiting
  • Headache, dizziness

These side effects are usually mild.

Tell your doctor immediately if you notice any of the following:

  • Confusion, excitation, depression
  • Breathing problems
  • Heart problems
  • Pins and needles, changes in sensation
  • Bleeding, fits
  • Abdominal pain, bloating
  • Addiction

These are serious side effects. You may need urgent medical attention. Serious side effects are rare. Other side effects may occur as a result of other medications received, so check with your doctor if you have any concerns.

If any of the above happen, tell your doctor immediately or go to casualty at your nearest hospital

Other side effects not listed above may also occur in some patients. Tell your doctor if you notice anything else that is making you feel unwell.

Ask your doctor if you don’t understand anything in this list.

Do not be alarmed by this list of possible side effects. You may not experience any of them.

After using Entonox


Entonox is stored at ambient temperature in cylinders by your doctor, dentist, ambulance or hospital under specific instructions.


All cylinders are the property of the manufacturer as defined on the cylinder label and are to be returned to the manufacturer.

Product Description

What it looks like

Entonox is a clear, colourless, slightly sweet smelling, nonirritating gas supplied in blue (ultramarine) and white cylinders as determined by AS4484

Cylinder sizes include 1.5L, 3.0L, 10L, 25L, 50L as measured by nominal water capacity.


Nitrous oxide component

Nitrous oxide- 98% v/v min

Carbon dioxide- 300ppm v/v max
Carbon monoxide- 5ppm v/v max
Oxides of nitrogen- 2ppm v/v max
Water (vapour)- 67ppm v/v max

Oxygen component

Oxygen- 99.5% v/v min

Carbon dioxide- 300ppm v/v max
Carbon monoxide- 5ppm v/v max
Water (vapour)- 67ppm v/v max

Manufacturer/Distributor/ Supplier

BOC Gases Australia Limited
Riverside Corporate Park
10 Julius Ave.
North Ryde NSW 2113

AUST R 34470

This leaflet was prepared in September 2001 and modified on the 27 March 2008.

Published by MIMS September 2019