just found some interesting info here:
http://www.babycentre.co.uk/refcap/542577.html
What are the advantages of pethidine?
Helps you relax
Administered by a midwife no need for a doctor
Can be used for a home birth although not all midwives feel comfortable with this.
What are its disadvantages?
It may make you very sleepy some women don't even know they've given birth!
It can make you feel sick or vomit even if you have an anti-emetic
It may make you feel dizzy
You may be drowsy while contractions are building up, but wake up suddenly when the contractions reach their peak
It may slow labour down
It crosses the placenta and may affect your baby's breathing
Your baby may need to have an injection (narcan) as soon as she is born to reverse the effects of the pethidine in her system
She may be very sleepy for a few days and not interested in feeding
Breastfeeding is less likely to be successful if you have pethidine in labour
Some recent evidence suggests that babies whose mothers have pethidine in labour are more likely to develop addictions in later life.