Would you recommend an antihistamine to someone starting an antidepressant or birth control in case they get nauseous?

With caution in gals: I don't see that as an unreasonable move if the patient is particularly sensitive from a GI point of view. I would only caution that antiemetics (and especially the -zines can and do cause permanent tic disorder in a small percentage of young women which remains lifelong even if drug is stopped.

Need more info: There are so many medications on the market, some OTC, some by Rx and some that will affect the fetus. You must consult with your OB-GYN for the best medicine for you.