Yes, you can take penicillin while breastfeeding. Penicillins are considered compatible with breastfeeding and are among the most commonly prescribed antibiotics for nursing mothers. Only trace amounts reach your baby through breast milk, and serious reactions are rare.
How Much Reaches Your Baby
When you take penicillin, a small fraction of the drug passes into your breast milk. For broad-spectrum penicillins, the milk-to-plasma ratio is around 38%, which sounds like a lot but refers to the concentration ratio, not the total amount your baby actually ingests. Because your baby drinks a relatively small volume of milk and absorbs it differently than you absorb your oral dose, the actual quantity that enters their system is very low. The American Academy of Family Physicians notes that penicillins are excreted in milk in trace amounts.
For amoxicillin (one of the most commonly prescribed penicillins), breast milk levels peak about 4 to 5 hours after you take a dose. This means you can reduce your baby’s exposure even further by nursing right before you take your next dose, when levels in your milk are at their lowest.
Possible Side Effects in Your Baby
Most babies show no reaction at all. In one small study of 12 breastfed infants whose mothers were taking penicillin V, seven appeared completely normal. Three had looser stools than usual, and one developed a mild rash on the buttocks toward the end of the treatment course. These effects were mild and temporary.
The side effects to be aware of include:
- Loose stools or diarrhea: The most commonly reported change, caused by small shifts in your baby’s gut bacteria. This is usually mild and resolves once you finish your course.
- Oral thrush: A white coating on your baby’s tongue or inside their cheeks. Antibiotics can disrupt the balance of yeast and bacteria in the mouth, occasionally allowing yeast to overgrow.
- Skin rash: Occasionally reported, typically mild and short-lived.
- Irritability or drowsiness: Rare, and often attributable to other causes like normal fussiness or illness.
None of these effects have been reported frequently enough to warrant avoiding penicillin during breastfeeding. They tend to resolve on their own once the antibiotic course ends.
Allergic Reactions
A common worry is whether your baby could have an allergic reaction to penicillin passed through breast milk. This is extremely unlikely given the tiny amounts involved, but as a precaution, watch for any rash that appears suddenly or any signs of breathing difficulty. These would warrant immediate medical attention, just as they would with any new exposure. There is no strong evidence that breast milk exposure to penicillin causes your baby to develop a penicillin allergy later in life.
Effects on Your Baby’s Gut Bacteria
Your baby’s developing gut microbiome is sensitive to antibiotic exposure, and this is the one area where researchers have found measurable effects. Studies on mothers who received penicillin have shown temporary decreases in beneficial bacteria like Bifidobacterium in their infants during the first weeks of life, along with increases in other bacterial families. Penicillin had a milder impact on infant gut bacteria than broader-spectrum antibiotics like cephalosporins.
These shifts are generally temporary. The infant gut microbiome is remarkably resilient, and continued breastfeeding itself is one of the most powerful ways to support healthy bacterial colonization. In fact, one of the reasons penicillin is preferred during breastfeeding is precisely because it leaves a lighter footprint on gut bacteria compared to broader-spectrum alternatives.
How to Minimize Your Baby’s Exposure
If you want to be extra cautious, the simplest strategy is timing. Nurse your baby right before you take your dose. This gives your body several hours to metabolize the drug before the next feeding, meaning your baby feeds when milk concentrations are lowest. For amoxicillin specifically, peak milk levels hit around 4 to 5 hours after a dose, so feeding just before you take it puts the most distance between your baby and that peak.
Beyond timing, the most important thing is to finish your full course of antibiotics. Stopping early because you’re worried about breastfeeding can lead to incomplete treatment and antibiotic resistance. The benefits of both treating your infection and continuing to breastfeed outweigh the small risks of trace antibiotic exposure through milk.
Which Penicillins Are Compatible
The penicillin family includes several commonly prescribed antibiotics: penicillin V (the standard oral form), amoxicillin, and amoxicillin-clavulanate. All are considered compatible with breastfeeding. Amoxicillin is one of the most frequently studied antibiotics in nursing mothers, and its safety profile during lactation is well established. Penicillin V similarly passes into milk in small amounts with only occasional, mild effects reported in infants.
If your doctor has prescribed a penicillin-type antibiotic and you’re breastfeeding, there is no need to pump and dump, supplement with formula, or interrupt breastfeeding. You can continue nursing on your normal schedule while completing your treatment.