To help control labor pain and stress, an injection of pain medicine can be given into a vein (intravenous) or into the muscle (intramuscular). The most common pain medicines used are opioids. Opioids are also known as narcotics. Examples of opioids include fentanyl, morphine, and nalbuphine.
How opioids work for labor pain
Opioid analgesics suppress your perception of pain and calm your emotional response to pain by reducing the number of pain signals sent by the nervous system and the brain's reaction to those pain signals.
An opioid can help you relax between contractions and decrease the pain but does not take the pain away completely. Opioids make you drowsy for a short time and can slow your labor. But opioids are less likely than epidural anesthesia to cause you to have a forceps or vacuum delivery.1
The most common side effects of opioids include:
Opioids are not used when you are close to delivery, because they can affect a newborn's breathing. They can also make the baby sleepy and less interested in breast-feeding if they are given close to delivery.