Is it safe to take phenobarbital while pregnant or breastfeeding?

No: Not really a straight forward yes/no answer. Is rated as category d which means it has been shown to cause serious problems in fetus in humans. However all antiseizure medications have this warning. It is important to prevent seizures in pregnancy for the well being of the mother and fetus so there are risks and benefits to using and not using antiseizure drugs.

Yes & no: Phenobarbital is considered a category d drug during pregnancy primarily because of the withdrawal syndrome newborns go through at birth. That said it is less worrisome than some anti-convulsants. Choice to continue should be made in consultation with treating physicians. Use in lactation is relatively safe, yet baby gets about 1/4 of mom's dose & sedation or withdrawal problems can be seen.