The need for mothers with hypothyroidism or hyperthyroidism to continue taking medication during breastfeeding and the effect on the infant is a matter of concern. This is explained according to the relevant literature for clinical reference. 1. Mothers with hypothyroidism taking thyroid hormone (T4) therapy have no effect on the thyroid function of their babies as long as the mother’s thyroid hormone level is normal. If a mother takes 600 mg/day of propylthiouracil, the infant receives only 149 micrograms, which is equivalent to 3 mg/day for a 70 kg adult, based on a body weight of 4 kg. This is equivalent to 3 mg/day for a 70-kg adult. 2. 2 hours after oral administration of 20-30 mg/day of tabazol, the infant’s serum tabazol is less than 0.03 mcg/100 ml, which is far below the therapeutic dose range. 3. Clinical studies: 1. The infant’s nail function was not significantly affected by 200 mg/day of tabazol or 600 mg/day of propylthi for nursing mothers. 2.Tabazol taken by breastfeeding mothers has no effect on the infant’s mental and physical development. 3. No allergic reactions were found in infants when antithyroid drugs were taken by nursing mothers. 4. Conclusion: 1. It is safe for mothers to take antithyroid drugs during lactation, whether they have already taken them during pregnancy or started taking them after delivery. 2. It is safe to take a dose of 20 mg/day of tabazol and less than 450 mg/day of propylthi during lactation. 3. The medication should be taken immediately after breastfeeding so that there can be a gap of 2 to 4 hours until the next breastfeeding. 4. Check the mother’s thyroid function regularly so that the dose can be adjusted, but it is generally not necessary to check the infant’s nail function.