Some antihistamines that are compatible with breastfeeding include Claritin, Reactine, and Aerius. Reactine may cause slight drowsiness in the baby, but adverse effects are unlikely. If you previously used one of these medications and it worked well for you, you can continue with that one. Otherwise, you may need to try them out to see which one provides the best relief for you. It may take 5 to 7 days to determine the maximum effectiveness of an antihistamine. In addition, using a saline nasal rinse and cortisone nasal sprays like Nasonex, Flonase, or Nasacort is safe while breastfeeding.