I take up to 4 mgs of xanax a day and I'm 8 weeks pregnant. I'm worried about the fetus...?

It probably didn't do any damage that early in pregnancy. Lots of women don't know they are pregnant and continue to do things like that. As long as you are not doing it now, it should be ok. It you are worried ask to get an early ultrasound done. Please don't terminate the baby though. You should be ok!