Is it safe to drink expectorant during pregnancy?

Avoid: Plain Guaifenesin, the active ingredient in Mucinex (guaifenesin) and Robitussin, is pregnancy Class C. That means it has not been formally tested on humans but has had some adverse effect on animals during testing. There is very little that is considered really safe in pregnancy. If sick, rest, drink plenty of water, and eat as well as possible. Not much different advice from the rest of the pregnancy.