If a pregnant woman takes medicine that causes drowsiness, does the baby become drowsy also?

I have avoided medication for the most part during my pregnancy. The one thing I very occasionally take (after checking with my Obgyn) is Benadryl for allergies. It causes me to become extremely tired and I’m wondering if taking medicine like this also causes my baby to become tired? Does it enter his system at all? Just curious as to how it works…