This is what kellymom.com says
When can I begin using a pacifier?
It is recommended that pacifiers and other types of artificial nipples be avoided for at least the first 3-4 weeks. I'd personally suggest that
most breastfed babies - if they get a pacifier at all - would be better off without a pacifier until mom's milk supply is well established (6-8 weeks, usually) and the 6 week
growth spurt is over. That way you've established a good milk supply and don't lose any much-needed breast stimulation to a pacifier
Here is the link if anyone wants to read up:
http://www.kellymom.com/bf/start/concerns/pacifier.html