Can you take acyclovir while breastfeeding?
What LactMed says
The National Library of Medicine’s own summary, quoted in full. We do not write a verdict of our own on this question, and we do not compress theirs into a label.
Even with the highest maternal dosages, the dosage of acyclovir in milk is only about 1% of a typical infant dosage and would not be expected to cause any adverse effects in breastfed infants. Acyclovir is considered a treatment of choice for Herpes infections during breastfeeding. Topical acyclovir applied to small areas of the mother's body away from the breast should pose no risk to the infant. Only water-miscible cream or gel products should be applied to the breast because ointments may expose the infant to high levels of mineral paraffins via licking.
Quoted from Acyclovir — Drugs and Lactation Database (LactMed®), National Institute of Child Health and Human Development, revised February 15, 2026.
What LactMed would consider instead
LactMed ends this record by naming the drugs it would consider in place of acyclovir. Whether any of them fits depends on what you are treating — this is the database’s list, not a recommendation from us.
How much acyclovir gets into breastmilk
Maternal Levels. A 4-month-postpartum woman was taking 200 mg of acyclovir orally 5 times daily every 4 hours while awake. After 4 days of therapy, milk samples were taken 9 hours after the previous dose and at 4 times after a 200 mg dose. The lowest milk level of 427 mcg/L occurred 30 minutes after the first dose. At 3.2 hours after the dose, the milk acyclovir level was 1.3 mg/L and apparently still increasing.
A woman who was 1 year postpartum was taking acyclovir 200 mg orally 5 times daily. Milk levels taken immediately before a dose during 5 days of therapy ranged from 0.78 to 1.07 mg/L. Acyclovir in milk samples taken after the last dose decreased with a half-life of 2.8 hours.
A woman who had taken oral acyclovir 400 mg 3 times daily for 3 days in the peripartum period had a breastmilk acyclovir level of 54 mcg/L at 5 days after her last dose of acyclovir.
A mother nursing her 7-month-old infant took acyclovir 800 mg orally 5 times a day. Three milk acyclovir levels on days 5 and 6 of therapy ranged from 4.2 to 5.8 mg/L, with the highest level 9.4 hours after the previous dose. The authors estimated that a fully breastfed infant would receive a daily dosage of 0.73 mg/kg of acyclovir at this maternal dosage or about 1% of the maternal weight-adjusted dosage.
A woman who was 6 weeks postpartum received intravenous acyclovir 300 mg (5 mg/kg) three times daily for 5 days. Milk samples were taken every 6 hours after the last dose. The peak level was 7.3 mg/L and the drug was detectable in milk for up to 88 hours after the last dose. Using the level 6 hours after the last dose, a fully breastfed infant would receive a daily dosage of 1.1 mg/kg with this maternal dosage regimen.
Infant Levels. A 4-month-old infant whose mother was taking 200 mg orally 5 times daily was breastfed just before a dose. The infant's urine collected over the next 2 hours contained a total of 27 mcg of acyclovir.
What has been seen in breastfed infants
The mother of a 4-month-old infant noticed no adverse effects in her breastfed infant while she was taking an acyclovir dosage of 800 mg orally 5 times daily.
A mother with necrotizing herpes simplex keratitis was treated with 3% acyclovir ointment to the affected eye as well as acyclovir 500 mg orally, both 5 times a day. She continued oral acyclovir for 1 year and breastfed during treatment. At the 3 months follow-up, the baby was clinically healthy.
Effects on milk supply
Relevant published information was not found as of the revision date.
Frequently asked questions
Can you take acyclovir while breastfeeding?
What the NIH's Drugs and Lactation Database says about Acyclovir while breastfeeding — quoted in full. The full record is quoted on this page, and the decision is one to make with the person who prescribed it — LactMed itself states it is not a substitute for professional judgement.
What can I take instead of acyclovir while breastfeeding?
LactMed lists Valacyclovir as alternate drugs to consider. That is the database's own list for this drug — whether any of them suits you depends on what you are treating.
Does acyclovir pass into breastmilk?
LactMed's measured drug levels for acyclovir are quoted in full on this page, under "How much gets into breastmilk".
Do I need to pump and dump after taking acyclovir?
LactMed does not frame its records that way — it reports measured drug levels in milk and what has been observed in breastfed infants, which is what this page quotes. "Pump and dump" advice for a specific drug and dose should come from your clinician or a pharmacist, not from a general rule.
More on acyclovir
LactMed states that the information it presents is not a substitute for professional judgement, and that you should consult your healthcare provider for breastfeeding advice related to your particular situation. Nothing on this page is medical advice.