Asprin can trigger the release of histamine from mast cells in sensitive individuals. An exhausted working mother wants to know if she can take melatonin pills to help her get more restful sleep. Since there have been animal studies linking animal studies with cancer, she is especially worried that melatonin is hazardous for her nursing infant. Only very small amounts are needed to have a biological effect. Therefore, it is unlikely that large amounts will get into the milk to harm the baby, since the mother will be taking such low doses.
Drugs are usually only a problem during early pregnancy.
Accutane, used in the treatment of acne, can cause birth defects. A young couple is working on removing lead paint from an old house. However, they are concerned if exposure to lead can be related to their current apparent infertility. Lead could probably damage the child in utero so the woman should avoid lead, but the man should have no problem with lead exposure. Lead won't affect the woman with regard to fertility, since the placenta is an effective barrier to toxicants, but the man may need to avoid exposure.