Animal studies have not found montelukast to harm a developing fetus. However, there is no adequate evidence regarding the safety of montelukast during human pregnancy. The FDA does note that there are rare reports of congenital limb defects in children of women taking montelukast, but that most were also taking other medications and no definitive link has been established. Based on all the available evidence, the FDA classes montelukast in Pregnancy Category B, meaning it is considered safe to use during pregnancy if there is a clinical need. Montelukast has been shown to pass into breast milk in animal studies but it is not known whether it is excreted in human breast milk. If you are pregnant, planning on getting pregnant, or are a nursing mother, you should speak to your doctor about montelukast and any other medications you are taking.