Labour pain relief: Gas and air (Entonox)

What is Entonox?

Entonox is a colourless, odourless gas (Knuf and Maani, 2020) that is usually made up of half nitrous oxide and half oxygen (NICE, 2007). Some hospitals add other substances to make it more effective but they may make the woman more sleepy (OAA, 2019).

Why is Entonox used in labour?

A lot of women use Entonox in labour because many find it to be the best option from a range of inhaled pain relief (CQC, 2019). Entonox has no negative effect on uterine contractions, and you and your baby get rid of it quickly from your bodies (Jones et al, 2012).

How is Entonox used in labour?

It’s self-administered so you breathe in Entonox through a mouthpiece or mask that you grab when you need it.

You control the amount of Entonox you use but it is important to get the timing right to get the best effect. You should start breathing Entonox as soon as you feel a contraction coming on so you will get the full effect when the pain is at its worst. You should not use it between contractions or for long periods as this can make you feel dizzy and tingly (OAA, 2019). 

Entonox takes 15 to 20 seconds to work effectively (NHS, 2017). It is simple and quick to act and wears off in minutes (OAA, 2019).

The pain-relieving effect is caused through the release of the body's own opioids, so it has a similar effect to morphine (Knuf and Maani, 2020).

How effective is Entonox?

Entonox is said to be of ‘moderate’ help with pain and is, surprisingly, more effective at easing pain than opioids (Jones et al, 2012; OAA, 2016, 2019). 

Can everyone use Entonox?

Some women say Entonox makes them feel sick so they might want to avoid it.

Nitrous oxide can cause dreaming and hallucinations, so people with severe psychiatric disorders should avoid it (Knuf and Maani, 2020).

Using Entonox for over 24 hours can deplete the body's stores of vitamin B12 (Knuf and Maani, 2020). Vitamin B12 levels might be checked if you are at risk of a deficiency.

What are women’s experiences of Entonox?

Women who use it like being able to control it themselves (NHS, 2020). But Entonox can make some women feel nauseous and light-headed (NICE, 2007).

Does Entonox have any side effects?

There are no significant side effects for women or babies when used appropriately, i.e. during contractions only (Jones et al, 2012; NHS, 2020). Slight side effects are feeling dizzy or being sick, and women often say that it gave them a dry mouth (Jones et al, 2012; OAA, 2016; Lowth, 2017; NHS, 2020).

It does not harm your baby (OAA, 2019).

Does Entonox affect labour or breastfeeding?

It has no impact on how labour progresses, and there is no suggestion of any impact on breastfeeding (OAA, 2016). 

Does Entonox have any long-term effects?

None on the person using it. There are concerns about its effect on midwives, who have a greater exposure (Robertson, 2006), and on the environment (Campbell and Pierce, 2015).

How long do the effects of Entonox last?

You can stop taking it at any point if you choose. The effects of Entonox wear off in minutes (OAA, 2019).

Where and when can I use Entonox during labour?

You can have Entonox wherever you plan to give birth. If you’re planning a home birth, the midwife will bring Entonox with them. You can use it at any time during labour (OAA, 2019).

Can my partner help with Entonox?

Your partner can help by holding the mouthpiece between contractions, while you’re not using it, and then offering it back to you. This is particularly important if you’re in a bath or birth pool as you don’t want the mouthpiece to slip into the water.

Can I use Entonox with other types of pain relief?

You can use Entonox at the same time as TENS, water, pethidine/diamorphine or self-help measures (e.g. hypnobirthing). 

Will I need any extra procedures with Entonox?

There is no need for extra monitoring or any other additional procedures with Entonox (OAA, 2016).

Are there any other considerations with Entonox?

When discussing options for working with the pain of labour, your midwife might mention the environmental impact of Entonox. This is not to discourage you from using it but because some women might make an informed decision not to. Entonox is a greenhouse gas that accounts for over 2% of the NHS carbon footprint, and about a third of that is used by women in labour (Sulbaek et al, 2012; Sustainable Development Unit, 2013).  

Other pain relief options also have environmental impacts but Entonox is the first one that has been highlighted (Sustainable Development Unit, 2013). NHS Trusts will also be working to address the hospital’s environmental impact in other ways, such as lower temperatures, improved recycling, and transport (Sustainable Development Unit, 2013).

This page was last reviewed in March 2021.

Further information

Our support line offers practical and emotional support with feeding your baby and general enquiries for parents, members and volunteers: 0800 640 5599.

We also offer antenatal courses which are a great way to find out more about pregnancy and life with a new baby.

Research from the Royal College of Obstetricians and Gynaecologists (RCOG) about the use of water as pain relief in labour.