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Opioids are painkillers and they all work in a similar way. Opioids commonly used on labour wards include morphine, pethidine, and diamorphine. Examples of other opioid drugs include dihydrocodeine, fentanyl and remifentanil. 

Opioids may be given by mouth (oral), by injection into a muscle (intramuscular) or by injection into a vein (intravascular). Opioids can also be given through an epidural or by spinal injection.

Although opioids are similar drugs, some may work better than other depending on how they are given. For example, research has shown that women who receive an injection of diamorphine into a muscle are more likely to be satisfied with their analgesia (pain relief) when compared to when pethidine is used for the injection.

Facts about opioids:

  • A midwife usually gives opioids during labour by injecting them into a large muscle in your arm or leg.
  • The pain relief is often limited. You will start to feel the effects after about half an hour and they may last a few hours.
  • Opioids are less effective at easing pain in labour than Entonox (gas and air).
  • Although pain relief may be limited, some women say it makes them feel more relaxed and less worried about the pain.
  • Other women are disappointed with the effect of opioids on their pain and say they feel less in control.

Potential side effects of opioids include:

  • They may make you feel sleepy.
  • They may make you feel sick, but you can be given anti-sickness medicine to stop this.
  • They slow down the emptying of your stomach, which might be a problem if you need a general anaesthetic.
  • They may slow down your breathing. If this happens, you may be given oxygen through a face mask and have your oxygen levels monitored.
  • They may make your baby slow to take their first breath, but your baby can be given an injection to help with this.
  • They may make your baby drowsy, and this may mean that they cannot feed as well as normal (especially if you are given pethidine).
  • If you are given opioids just before you give birth to the baby, the effect on your baby is very small.


  • Olofsson C, Ekblom A, Ekman-Ordeberg G, Hjelm A, Irestedt L. Lack of analgesic effect of systemically administered morphine or pethidine on labour pain. British Journal of Obstetrics and Gynaecology. 1996;103:968-972.

  • Tuckey JP, Prout RE, Wee MKY. Prescribing intramuscular opioids for labour analgesia in consultant-led maternity units: a survey of UK practice. Int J Obstet Anesth. 2008 Jan;17(1):3-8. Epub 2007 Nov 5.

  • Wee MYK, Tuckley JP, Thomas P, Bernard S and Jackson D. The IDvIP trial: A two centre double blind randomised controlled tril comparing i.m. diamorphine and i.m. pethidine for labour. International Journal of Obstetric Anaesthesia. 2012;21(S1) S15.