Is Mucinex safe while breastfeeding?

What does the evidence say about Mucinex while breastfeeding?

1. Neither the excretion of guaifenesin in milk nor its effect on breastfed infants has been studied, and it is unlikely that usual maternal doses would harm a nursing infant, especially in infants over 2 months of age. 1
2. Guaifenesin is an expectorant that thins and loosens mucus in the throat and lungs, and it is also sold combined with other medications in over-the-counter cough and cold preparations. 2
3. Plain Mucinex is a single-ingredient extended-release tablet of guaifenesin 600 mg, labeled for adults at 1 or 2 tablets every 12 hours and no more than 4 tablets in 24 hours, taken with a full glass of water. 3
4. Mucinex D is guaifenesin 600 mg plus pseudoephedrine HCl 60 mg per tablet, so the D formulation is a decongestant combination rather than a plain expectorant. 4
5. At recommended doses only a small amount of pseudoephedrine passes into breast milk and side effects in nursing infants are not expected, but it might lower the amount of milk your body makes. 5

How Mucinex changes by nursing stage

• Early weeks. Supply is still being established, so this is the stage where the pseudoephedrine in Mucinex D matters most. MotherToBaby notes pseudoephedrine might lower the amount of milk your body makes.
• Established nursing. LactMed notes that any harm from usual maternal guaifenesin doses is unlikely, especially in infants over 2 months of age, which is the window most people are asking about.
• Weaning. Fewer feeds means less transfer, and supply effects matter less once you are winding down. The 4-tablet daily ceiling on the extended-release products is unchanged either way.

What is actually in each Mucinex box