Hydroxyurea is chemotherapy drug and is classified as an "antimetabolite." Animal and human studies have revealed evidence of side effects with hydroxyurea, pregnancy & breastfeeding. This drug can cause fetal malformations, decreased fetal viability and developmental delays. Also hydroxyurea has been reported to lower men sperm count as well. If you are a female, you should use effective birth control while taking hydroxyurea and for at least 6 months after stopping your treatment. If you are a male, you and your female partner should use effective birth control while taking hydroxyurea and for at least 6 months or at least 1 year (Droxia, Hydrea) after stopping your treatment. Read more information below.