FDA pregnancy category B. Penicillin V is not expected to be harmful to an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant during treatment. Penicillin V can make birth control pills less effective, which may result in pregnancy. Before taking this medicine, tell your doctor if you use birth control pills. Penicillin V can pass into breast milk and may harm a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby.