<p>Pregnancy category B. There have been no adequate and well controlled studies concerning the safety of Acyclovir in pregnant women. It should not be used during pregnancy unless the benefits to the patient clearly outweigh the potential risks to the fetus. Acyclovir should only be administered to nursing mothers if the benefits to the mother outweigh the potential risks to the baby. There is no experience of the effect of Acyclovir on human fertility.</p>