Morphine is stronger than Pethedine. Both are opiates so if Pethedine makes you feel yuck then I would think that Morphine would too. I have just done a pharmacology course and (in NZ at least) Morphine is not usually offered during labour as it crosses the placenta and can cause respiratory distress in the newborn. The drug of choice here is currently Fentanyl which is a synthetic opiate with less side effects. Good luck xx