Laughing gas
Nitrous oxide
An anaesthetic and pain-relief gas, combined with oxygen for labour, ambulances and dental and minor procedures.
What is Nitrous oxide?
Nitrous oxide, often called laughing gas, is a gas used for pain relief and as part of anaesthesia. Combined with oxygen as a ready-mixed gas (Entonox), it is breathed in to ease pain during labour, in ambulances and for dental and minor procedures, giving fast, short-lasting relief you can control yourself. It is also used by anaesthetists alongside other agents during surgery. It is generally very safe for short-term use, but its key risk is that repeated or prolonged use inactivates vitamin B12, which can lead to nerve damage. It must also be avoided where trapped air could expand, such as in some lung, bowel or eye conditions.
Education and reference only. This is a plain-language guide to Nitrous oxide — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Nitrous oxide is a gas used both for pain relief and as part of general anaesthesia. For pain relief it is most often given ready-mixed with oxygen (as Entonox), which the person breathes in through a mouthpiece or mask, for example during labour, in ambulances, or for dental and minor procedures. It is also used by anaesthetists in the operating theatre alongside other anaesthetic agents. It is given and supervised by trained staff, who ensure it is mixed with enough oxygen and monitor the person.
How it works
Nitrous oxide is breathed into the lungs and quickly reaches the brain, where it dulls the sense of pain and produces a light, relaxed feeling; for pain relief during procedures it does not send people fully to sleep. Because it is taken up and cleared by the lungs very rapidly, the effect comes on within moments and fades quickly once breathing stops, which is why it suits self-controlled use, such as a mother breathing Entonox during contractions. With repeated or prolonged exposure it can interfere with vitamin B12, a vitamin the nerves need, which is the basis of its main long-term risk.
Company & origin
Originated / developed by: Generic (long-established).
A long-established anaesthetic and pain-relief gas used widely in the UK, including for labour, in ambulances and for dental and minor procedures.
Practical use
How to take Nitrous oxide
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Nitrous oxide for pain relief is usually breathed in as a ready-mixed gas with oxygen (Entonox) through a mouthpiece or mask, under the guidance of trained staff.
- Breathe steadily as you start to feel pain, such as at the beginning of a contraction, so the relief builds; it works within moments and fades quickly when you stop.
- Tell staff about your medicines and any conditions, especially low vitamin B12, or any lung, bowel, ear or eye problems, before using it.
- Do not use it for prolonged periods or repeatedly without medical advice, because of the effect on vitamin B12.
- In the operating theatre, the anaesthetist gives it alongside other anaesthetic agents and monitors you throughout.
Weighing it up
Advantages & disadvantages of Nitrous oxide
Advantages
- Gives fast, short-lasting pain relief that the person can control themselves, ideal for labour and minor procedures.
- Comes on and wears off very quickly, with the gas cleared rapidly by the lungs.
- Widely available and easy to use in many settings, including ambulances and dental clinics.
Disadvantages
- Repeated or prolonged use inactivates vitamin B12, which can lead to nerve damage.
- Must be avoided where trapped air could expand, such as in some lung, bowel, ear or eye conditions.
- Can cause light-headedness, nausea or a floaty, giggly feeling at the time.
Practical use
Good to know
Used as a ready-mixed gas with oxygen (Entonox), nitrous oxide gives fast, short-lasting pain relief that you breathe in and control yourself, which makes it popular in labour, ambulances and for dental and minor procedures; the relief comes and goes quickly. It can cause light-headedness, nausea or a giggly, floaty feeling at the time, which pass off rapidly. The most important long-term safety point is that repeated or prolonged use inactivates vitamin B12, which the nerves need, and this can lead to nerve damage with numbness, tingling and unsteadiness; this is why short, occasional use is generally safe but heavy or repeated recreational misuse is dangerous. It must also be avoided where there is trapped air or gas that could expand, such as certain lung, bowel, ear or eye conditions and after some types of eye surgery, because the gas can make trapped pockets bigger.
Who should not take it / use with caution
- It must be avoided where there is trapped air or gas that could expand, such as certain lung, bowel, ear or eye conditions and after some eye surgery.
- It is avoided or used with care in people who are low in vitamin B12, and repeated or prolonged use is discouraged.
- As with all anaesthetic agents, the team must know about your conditions and any previous problems with anaesthesia.
Monitoring
- Ensuring it is always given with enough oxygen and monitoring the person while it is used.
- For repeated or prolonged use, watching for signs of vitamin B12 deficiency such as numbness, tingling or unsteadiness.
- In theatre, continuous monitoring of breathing, oxygen levels, heart rate and consciousness alongside other anaesthetics.
Side effects
- Light-headedness, nausea, drowsiness or a floaty, giggly feeling at the time, which pass quickly.
- With repeated or prolonged use, nerve damage from inactivated vitamin B12, causing numbness, tingling and unsteadiness.
- Expansion of any trapped air, which can be harmful in certain lung, bowel, ear or eye conditions.
Key interactions
- Its effects add to those of other anaesthetics, sedatives, strong painkillers and alcohol, increasing drowsiness.
- Its effect on vitamin B12 matters more in people who are already low in B12 or who use it repeatedly.
- The anaesthetic team takes its effects into account alongside other agents during surgery.
Available as: A gas breathed in, usually ready-mixed with oxygen (such as Entonox) through a mouthpiece or mask, and used by anaesthetists in theatre.
Answers
Nitrous oxide: frequently asked questions
What is Entonox?
Entonox is nitrous oxide ready-mixed with oxygen, breathed in for fast, short-lasting pain relief, for example during labour, in ambulances and for minor procedures.
Will it send me to sleep?
For pain relief it does not send you fully to sleep; it dulls pain and gives a relaxed, floaty feeling that you can control by breathing it in.
Why is repeated or recreational use dangerous?
Repeated or prolonged use inactivates vitamin B12, which the nerves need, and this can cause nerve damage with numbness, tingling and unsteadiness.
Why can't everyone use it?
It must be avoided where trapped air could expand, such as in some lung, bowel, ear or eye conditions, because the gas can make trapped pockets bigger.
How quickly does it work and wear off?
It works within moments of breathing it in and fades quickly once you stop, which is why it suits self-controlled use during contractions or short procedures.
Authoritative sources
- BNF
- NICE CKS
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