Final answer:
Lifelong drug therapy is necessary for infants with congenital hypothyroidism to prevent cretinism, which leads to serious cognitive and developmental issues.
Step-by-step explanation:
The nurse is informing the family of an infant with congenital hypothyroidism that drug therapy will need to continue for life to prevent the development of a condition known as cretinism. Cretinism is a severe form of physical and mental development impairment that can occur in children due to untreated hypothyroidism. The thyroid hormone replacement therapy is crucial for normal growth, brain development, and overall bodily functions, which can significantly alter if the treatment is not adhered to consistently and monitored regularly.