A 35-year-old visits the midwife after a home pregnancy test indicated a positive result. The client informs the midwife that the pregnancy is not planned and that she has been taking progestin-only birth control pills for the past year. During the history taking, the client informs the midwife that she has been taking isotretinoin for her severe, recalcitrant cystic acne for three months before the pregnancy. The client drinks at least three bottles of beer a day and is taking cocaine on a daily basis. Based on the client’s history, which of the following substances is least likely to cause birth defects?
