Having a good understanding of drugs and how they can work with your labour can help you to make an informed choice when it comes to pain relief.  Here are the pros and cons of the different drugs you can use in your birth:

Nitrous Oxide (Gas)
A combination of nitrous oxide and oxygen.

Pros

• May ease the pain for transition
• Extra oxygen can be beneficial
• Can provide a distraction and get a woman to focus on the breath

Cons

• Nausea and vomiting
• Mother can feel drowsy and confused
• Face mask can be claustrophobic
• Does not relieve pain entirely

Pethidine
A narcotic drug that is similar to morphine and heroin.

Pros

• Sedates
• Has a secondary effect as a muscle relaxant, which may lessen pain and muscle tension, allow faster dilation
• May reduce pain

Cons

• Does not relieve pain entirely
• Creates a ‘high’, making concentration difficult
• Nausea, vomiting and dizziness
• Decreases oxytocin levels
• Depresses mother's breathing rate, which can reduce oxygenation of blood
• Pethidine crosses the placental barrier and depresses the baby’s respiratory centre; dangerous if baby is born 1-3 hours after injection.
• Difficulties establishing breastfeeding due to a depressed suckling reflex
• Opiate drugs cause delayed emptying of the stomach, increasing risk of aspiration syndrome, a serious complication if a general anaesthetic becomes necessary
• Increased likelihood of jaundice as the baby’s immature system works to eliminate the drug; may take 4-5 days to eliminate from system.
• Separation of mother and baby if problems are severe
• Research has demonstrated a potential link between exposure of some babies to pethidine during labour and their later development of an addiction to opiate drugs as teenagers

Epidural
Class of drugs called local anaesthetics such as bupivacaine, chloroprocaine, or lidocaine. 

Pros

• Reliable method of pain relief
• May help to control blood pressure
• Facilitates a forceps delivery if complications are encountered
• Allows mother to be conscious during Caesarean section
• Relief from pain may allow greater relaxation and faster dilation
• Relieving pain may increase mother's positive feelings around birth

Cons

• Decreases all natural hormonal influences
• Mother will be confined to bed
• In 10-15% of cases, anaesthetic may not take completely, leaving some areas not fully anaesthetised
• Epidural slows labour down so that oxytocin drugs may be needed to keep contractions going
• Blood pressure can fall dramatically, drip will always be inserted
• Increased likelihood that mother’s temperature will rise, and hence so will babies, increasing the risk of fetal distress
• A catheter is frequently used as a mother cannot feel bladder
• Severe pruritis (itching) for up to two-thirds of women
• Four times more likely for the baby to be in a posterior position
• Three times more likely to result in Caesarean sections for first-time mothers
• Baby may be difficult after the birth and hard to settle making breastfeeding and bonding an issue as baby tries to eliminate drugs from its system
• A woman twice as likely to experience postpartum haemorrhage (PPH) if they used an epidural
• Research demonstrates that a baby will receive almost eight times higher dosage relative to its body weight
• Paraplegia is a very, very rare but unpredictable complication
• In inexperienced hands, the covering of the spinal cord may be punctured, resulting in a leaking of spinal fluid and the mother will have a severe headache
• Muscles of pelvic floor are relaxed by anaesthetic and as a result the baby's head is less likely to rotate and forceps delivery may be necessary
• Mother will have reduced sensation of giving birth to her baby
• There is an absence of tone in the muscles that support the lower vertebrae and sacroiliac joints especially with a full epidural in place; this causes lack of stability in joints and moving mother may cause them to be misaligned, leading to a chronic backache that may last up to months after the birth