Amoxicillin is considered safe to take while breastfeeding. Only about 1% of a mother’s dose transfers into breast milk, which is far below the 10% threshold used to classify a drug as compatible with breastfeeding. Both the U.S. FDA and the Drugs and Lactation Database (LactMed) confirm that amoxicillin is acceptable for nursing mothers.
How Much Reaches Your Baby
Researchers measure drug transfer into breast milk using something called the relative infant dose, or RID. This estimates what percentage of the mother’s weight-adjusted dose the baby actually receives through milk. For amoxicillin, the RID is approximately 1%. Any drug with an RID under 10% is generally considered compatible with breastfeeding, so amoxicillin falls well within the safe range.
At these low concentrations, the amount of amoxicillin your baby ingests is not expected to cause any pharmacological effect. You do not need to pump and dump, skip feedings, or time your doses around nursing sessions. You can continue breastfeeding on your normal schedule throughout your course of treatment.
Possible Side Effects to Watch For
While serious reactions are not expected, small amounts of any antibiotic in breast milk can occasionally affect an infant’s digestive system. The reported side effects are uncommon and typically mild:
- Loose stools or diarrhea. Even trace amounts of an antibiotic can shift the balance of bacteria in a baby’s gut, sometimes leading to softer or more frequent bowel movements.
- Thrush. A yeast overgrowth in the baby’s mouth, appearing as white patches on the tongue or inner cheeks, can develop when gut bacteria are disrupted.
- Rash. A mild skin rash has been reported occasionally, though it’s unclear how often this is directly caused by amoxicillin in milk versus other factors.
These effects, when they do occur, typically resolve on their own once the mother finishes her antibiotic course. If your baby develops persistent diarrhea, refuses to feed, or you notice a widespread rash, those are worth a call to your pediatrician.
Effects on Your Baby’s Gut Bacteria
A 2025 study looking at mothers who received amoxicillin (combined with clavulanate) around the time of delivery found that the antibiotic did temporarily shift certain bacterial populations in their infants’ guts, particularly groups like Bacteroidales and Coriobacteriales. The study also detected changes in specific metabolic compounds, including bile acids and indole derivatives, that play roles in immune development.
These disruptions were transient, meaning they didn’t persist long-term. However, the research did find that the changes temporarily affected how well the infants responded to a pneumococcal vaccine. This is an area of ongoing scientific interest, but it applies most directly to antibiotics given during labor and delivery at higher doses, not to the trace amounts that transfer through breast milk during a standard outpatient prescription.
If Your Baby Has a Penicillin Allergy
Amoxicillin belongs to the penicillin family. If your baby has a known or suspected penicillin allergy, the small amount in breast milk could theoretically trigger a reaction, though this scenario is rare in young infants. True penicillin allergies are uncommon in newborns because allergic sensitization usually requires direct exposure.
If your baby has previously reacted to a penicillin-type antibiotic, let your prescriber know. Several other antibiotic classes are also considered safe during breastfeeding, including cephalosporins, macrolides (the family that includes common alternatives for respiratory infections), and metronidazole. Your doctor can choose one that avoids the penicillin family entirely.
Why Skipping Treatment Is Riskier
If you’ve been prescribed amoxicillin for an infection, leaving that infection untreated poses a greater risk to both you and your baby than the tiny amount of drug that passes through your milk. Untreated bacterial infections can worsen, lead to complications, and potentially interfere with your ability to breastfeed if you become too ill. Completing the full course of antibiotics as prescribed is the best approach for your recovery and for maintaining your milk supply.
There is no need to interrupt breastfeeding while taking amoxicillin at standard prescribed doses. The drug has decades of use in nursing mothers, and the evidence consistently supports its safety profile during lactation.