Can I take cefalexin while pregnant or breastfeeding?
A plain-words look at what the NHS, the US drug label and LactMed say about cefalexin.
In short
Pregnancy: Cefalexin can be taken at any point in pregnancy.
Breastfeeding: You can take cefalexin while breastfeeding.
Your doctor, midwife or pharmacist can help you decide.
What this means for you
Pregnancy
- There's no evidence that it harms the baby.
- Treating an infection while you're pregnant matters, because if it's not treated it could make you ill.
Breastfeeding
- Just tiny amounts of cefalexin reach breast milk, so it does not normally cause side effects in your baby.
- A few babies have, however, had diarrhoea from it.
- Treating an infection while you're breastfeeding matters, because if it's not treated it could make you ill.
- If you have any worries, contact your health visitor, midwife, doctor or pharmacist promptly.
- This includes if your baby is not feeding as well as they usually do; is being sick or has diarrhoea; or has oral thrush (a fungal infection in the mouth) or a skin rash.
Talk to your doctor or pharmacist
This page is educational, not advice for your own situation. Talk to your doctor, midwife or pharmacist before you start, stop or change any medicine in pregnancy or while breastfeeding.
The details: what each source says
Cefalexin in pregnancy
The NHS says
Cefalexin can be taken at any point in pregnancy. There's no evidence that it harms the baby.
Treating an infection while you're pregnant matters, because if it's not treated it could make you ill.
In our words, from the NHS page Cefalexin (nhs.uk). Contains public sector information licensed under the Open Government Licence v3.0 (OGL v3.0). The NHS does not endorse this site.
The US drug label says
8.1 Pregnancy Pregnancy Category B There are no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed. Reproduction studies have been performed on mice and rats using oral doses of cephalexin monohydrate 0.6 and 1.5 times the maximum daily human dose (66 mg/kg/day) based upon body surface area basis, and have revealed no evidence of impaired fertility or harm to the fetus.
Prescribing label, section “8.1 Pregnancy”: Cephalexin (oral), Bryant Ranch Prepack. Label on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.
Cefalexin while breastfeeding
The NHS says
You can take cefalexin while breastfeeding.
Just tiny amounts of cefalexin reach breast milk, so it does not normally cause side effects in your baby. A few babies have, however, had diarrhoea from it.
Treating an infection while you're breastfeeding matters, because if it's not treated it could make you ill.
If you have any worries, contact your health visitor, midwife, doctor or pharmacist promptly. This includes if your baby is not feeding as well as they usually do; is being sick or has diarrhoea; or has oral thrush (a fungal infection in the mouth) or a skin rash.
In our words, from the NHS page Cefalexin (nhs.uk). Contains public sector information licensed under the Open Government Licence v3.0 (OGL v3.0). The NHS does not endorse this site.
LactMed says
Limited information indicates that maternal cephalexin produces low levels in milk that are usually not expected to cause adverse effects in breastfed infants. Cephalexin is an alternative for the treatment of mastitis.[1,2] Occasionally disruption of the infant's gastrointestinal flora, resulting in diarrhea or thrush have been reported with cephalosporins, but these effects have not been adequately evaluated. A rare case of a severe allergic reaction occurred in an infant previously exposed to intravenous cefazolin whose mother began taking cephalexin while breastfeeding. Cephalexin is acceptable in nursing mothers.
“Summary of Use during Lactation”, LactMed record “Cephalexin” (LM60), quoted verbatim. Everything LactMed reports about Cephalexin while breastfeeding.
The US prescribing label says
Nursing Mothers Cephalexin is excreted in human milk. Caution should be exercised when cephalexin is administered to a nursing woman.
Prescribing label, section “Nursing Mothers”: Cephalexin (oral), Bryant Ranch Prepack. Label on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.
Other names
UK brand names (per the NHS): Keflex.
US name: cephalexin.
Sources
- NHS, Cefalexin (nhs.uk), page last reviewed 5 April 2023. Paraphrased. Contains public sector information licensed under the Open Government Licence v3.0.
- US drug label: Cephalexin (oral), Bryant Ranch Prepack, human prescription drug, label effective 3 April 2026, set ID 06c2fb2e-0539-4f16-bac4-e15a575ca802. DailyMed (National Library of Medicine). Public domain; quoted verbatim.
- Drugs and Lactation Database (LactMed), National Institute of Child Health and Human Development (NICHD), via NCBI Bookshelf, record “Cephalexin” (LM60), bulk release of 22 September 2026. LactMed on NCBI Bookshelf. Public domain; quoted verbatim. LactMed is a registered trademark of the U.S. Department of Health and Human Services.
Sources checked 26 September 2026. How we source and check every page.
Educational summary of named sources, not medical advice.