 [ Symptoms ] can anti thyroid drugs such as methimazole that is what i am taking keep me from becoming pregnant i have hyperthyroid and had radioiodine 15 months ago but my thyroid is still over producing i am almost 28 years old and have a 6 year old son and desperately want to have another child i know that the medication i am on is not recommended during the first trimester and i have had 2 periods that were abnormal just wondering if maybe it was a posible pregnancy but the thyroid drugs caused my body to reject the pregnancy [ Disease ] hi this piece of info may help you tell your doctor if you are pregnant plan to become pregnant or are breast feeding methimazole should not be used during pregnancy or breast feeding if you become pregnant while taking methimazole call your doctor immediately methimazole may harm the fetus so with this in mind i would not plan to get pregnant just yet good luck