Labour pain relief: intramuscular opioids – pethidine and diamorphine

What are opioids?

Pethidine and diamorphine are opioids, which are medications derived and synthesised from the resin of the opium poppy.

Opioid drugs are most useful in early labour (Lowth, no date). They aim to alter your mood during labour so you're more relaxed and can rest or sleep (Lowth, no date).

The most common type of opioids used during labour are pethidine or diamorphine, although some hospitals use other types (Lowth, no date; OAA, 2019). Hospitals generally offer one of these types of opioid, but you can ask if you’d prefer a different one.

Up to 25% of women in the UK use pethidine or a similar opioid during labour (Moran et al, 2019).

How are opioids like pethidine used?

A midwife would usually inject pethidine or diamorphine into your thigh muscle (intramuscular) when you're in labour. These opioids take 20 to 30 minutes to work, and each injection lasts for two to four hours (Lowth, no date; OAA, 2019). Your midwife may repeat the dose after one to three hours if it isn't having enough effect (Lowth, no date). You'll also be given an anti-sickness medication at the same time (NICE, 2007).

Other forms of opioids that you might use would be those that are taken by mouth or directly into a vein, neither of which we cover in this article. See the section Are there any alternatives? below.

Are opioids good for labour pain relief?

While opioids are commonly used, they are less effective than Entonox, and their long-term effects are unknown (Sprawson, 2017; OAA, 2019). The advantage of opioids is that they’re well known, easily available for midwives and inexpensive (Sprawson, 2017).

There is some low-quality evidence that opioids will give you relief from pain but they might also make you more drowsy, nauseous and sick (Smith et al, 2018). Nobody knows whether pethidine or diamorphine is better for pain relief, or which one women in labour are more satisfied with (Smith et al, 2018).

NICE guidelines say that intramuscular opioids provide limited pain relief during labour (NICE, 2007). They also say that intramuscular opioids may have significant side effects in pregnant women (drowsiness, nausea and vomiting) and their babies (short-term breathing problems and drowsiness that may last several days) (NICE, 2007).

The pain relief from them is limited – you'll start to feel the effects of the opioid after about half an hour and the pain relief may last a few hours (OAA, 2019).

Are opioids suitable for everyone?

Some women already know that they react poorly to opioids and so would avoid them.

Pethidine can bring on involuntary muscle spasms, and so may not given to women who have high blood pressure caused by their pregnancy (Fortescue and Wee, 2005).

What are women’s experiences of pethidine or diamorphine?

Each woman responds differently to opioids for labour pain. It’s good to remember that labour pain is different from the pain of illness or trauma (Sprawson, 2017). Some women find opioids help them to feel more relaxed and less worried about the pain (OAA, 2019). Others find it disappointing as a pain reliever and feel less in control (Lowth, no date; OAA, 2019).

A systematic review found that while pethidine is known to ease labour pain for some women, the quality of evidence is low. When compared with a placebo, no clear differences were seen in women's satisfaction with their pain relief or the number of women asking for an epidural (Smith et al, 2018).

About half of the women taking part in one study said they were happy with the pain relief from pethidine that was used alongside other pain relief, such as gas and air. Some of the women said it was 'brilliant' and that they 'didn't feel a thing' but about half of the women said that they could 'feel everything' and it had made 'no difference' to the intensity of their contractions (Moran et al, 2019). Some women likened the effects of pethidine to drinking a lot of alcohol and some said it made them feel extremely sleepy (Moran et al, 2019).

What are the side effects of opioids like pethidine?

Side effects might include feeling woozy, sick or forgetful (NHS, 2017). You might need oxygen if your breathing is affected (OAA, 2019). Opioids can also make you too drowsy to push effectively (Lowth, no date).

Some women reported feeling disconnected from their labour and unable to focus on or process what was going on around them (Moran et al, 2019). Women who found it hard to stay focused during labour, because of the opioids, may have been more critical of themselves and more disturbed by their pain (Moran et al, 2019).

Are there any side effects for the baby?

Opioids cross the placenta and the baby cannot easily process them. So the most appropriate use for them is earlier in labour, when they can be processed by the mother's system (Lowth, no date). An extra dose will not be given if the birth is expected within three to four hours, although it is not easy to predict the timing of births.

Opioids in your baby's system can affect their breathing after birth. This can mean your baby is transferred to the neonatal unit for help with breathing (NHS, 2017). Some NHS Trusts offer an opioid antidote called naxolone to you and your baby if necessary (Lowth, no date). But there are concerns about a lack of benefits and long-term developmental problems for babies given naloxone (Moe-Byrne et al, 2018).

Drugs such as pethidine can cause a decrease in muscle function and oxygen levels, and can affect heart rates in newborns. There have also been reports of a direct link between the dose of drugs used in labour and the newborn’s sucking ability (Hemati et al, 2018).

Opioids can also make babies sleepy after birth, which can affect their normal instinctive behaviours (Lowth, no date).

Is there any impact on labour?

Your carers will recommend you don't go into water (like a birthing pool or bath) within two hours of being given opioids or if you feel drowsy (NICE, 2007).

Intramuscular opioids could delay stomach emptying, which might be a problem if you need a general anaesthetic during labour (OAA, 2019). They could also slow down your breathing, which would mean you're given oxygen through a face mask and would need to have your oxygen levels monitored (OAA, 2019).

How do opioids during labour affect breastfeeding?

Pethidine, diamorphine and other opioids may interfere with breastfeeding (NICE, 2007; OAA, 2019).

Pethidine can make a newborn less able to suck and breastfeed. It affects the mother's levels of the hormone oxytocin, which may delay lactation (Hemati et al, 2018).

There’s also the risk that if you and your baby are separated because your baby goes to the neonatal unit, that interrupts bonding and hence affects breastfeeding (Lowth, no date; NICE, 2007; NHS, 2017).

Does having opioids during labour have any long-term effects?

There are no reported long-term effects (Pereira et al, 2012).

Is there any impact on mental health?

Research has shown that some women said they felt out of control because they were dependent on the midwife to give them the drug (Thomson et al, 2019).

Some women reported that their care providers became more distant after having this kind of pain relief. This was particularly the case when they weren't looked after by the same midwife or care provider throughout their labour (Thomson et al, 2019).

Other experiences include not receiving enough support with breastfeeding because of having the drug (Thomson et al, 2019). This might reflect a real substandard level of care, or it could be because of distorted perceptions due to the drug (Thomson et al, 2019). 

The disconnection from labour and inability to focus on what's happening that some women report (Moran et al, 2019) could lead to negative feelings about the experience of labour and birth.

What happens if I don’t like opioids?

If you decide you want to use an opioid, you can ask for the lowest possible dose to see how you react to it. You can always have more but it takes two to four hours to wear off if you don’t like it.

Can midwives prescribe opioids such as pethidine?

Pethidine, diamorphine or other opioids are available in all birth settings (NICE, 2007). As midwives can administer opioids, they are widely available. Yet midwives who are caring for women in non-hospital environments, like at a home birth, might be cautious about using opioids because of their impact on babies.

When do women have pethidine during labour?

Pethidine or diamorphine tend to be offered early in established labour, for women who have had a long and tiring early labour.

Opioids should not be given too close to the birth because of the effect on the baby, although it is difficult to predict when the birth will be (Lowth, no date).

What can my birth partner do to help?

A birth partner can help the woman remain in a good position, comfortable, hydrated and emotionally supported.

Can I have pethidine (or other opioids) with other options?

If you’ve had opioids, you’ll be discouraged from using a birth pool until the drugs have worn off. You can use Entonox and TENS alongside opioids.

Would I need any additional procedures?

You’d be offered anti-sickness medicine at the same time as the opioid injection (Lowth, no date; NICE 2007).

Are there any alternatives?

Forms of opioids that may be offered as intramuscular injections during labour are pethidine, diamorphine, fentanyl and meptid (Lowth, no date).

While there is no national guidance, NCT practitioners have observed that morphine liquid that is taken by mouth may be offered in early labour – ask hospitals about this.

Remifentanil is an opioid that is given through a drip and is controlled by the mother.

This page was last reviewed in March 2021.

Further information

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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.