I haven't seen any evidence to support that having pain relief during labour might lead to increased chance of drug use by your child in later life, but it can mean a groggier baby if it is administered quite late on and hasn't worn off.
I would not go for an epidural myself as the chance of requiring further intervention to give birth is greatly increased by about 50%. Some women who have a long labour though find they are useful in allowing them some rest to save their energy for the delivery. Try other methods of pain relief first, epidural should be the last option as it can stop you feeling anything and might hinder the birth process if your labour develops quicker than expected.
Its a personal choice really based on your developing labour and how you are feeling.