Quick answer
Human data on cannabis exposure through breast milk are limited. THC, the main psychoactive compound in cannabis, passes into breast milk. Reported effects in infants include sedation, lethargy, poor feeding, and slower weight gain. Long-term effects on brain development are not known. The American College of Obstetricians and Gynecologists (ACOG) and the CDC advise against cannabis use during breastfeeding.
What transfers into breast milk
THC is fat-soluble. It concentrates in the fat of breast milk. A 2018 study in Pediatrics tested milk from 54 women who used cannabis. THC appeared in 63% of samples. Detection lasted up to 6 days after the last use. CBD also passes into milk. Concentrations depend on dose, route, and frequency. Smoked cannabis sends THC into milk faster than edibles.
what if i smoke weed once while breastfeeding
What studies report in infants
Most human evidence comes from case reports and small cohorts. Documented infant signs after milk exposure: sedation, poor sucking, and reduced weight gain. Prenatal exposure studies link cannabis to low birth weight and preterm birth. Those outcomes come from placental transfer, not milk. Data on milk exposure alone are weaker.
What is not known
No large study tracks children exposed to THC through milk past age 3. Effects on behavior, memory, and school performance are unknown. The dose an infant absorbs from milk is lower than the dose from the placenta. CBD and other cannabinoids have less data than THC. Contaminants in smoked cannabis, such as tar and carbon monoxide, add risk.
What If I Smoke Weed Once While Breastfeeding?
Guidance from medical groups
ACOG recommends that women avoid cannabis while breastfeeding. The CDC states that THC passes into milk and that effects on infant development are not known. LactMed advises monitoring the infant for sedation and poor feeding if a mother uses cannabis. The American Academy of Pediatrics recommends counseling mothers to abstain. Some clinicians suggest waiting 6 days after a single use before resuming breastfeeding. That interval comes from detection data, not from safety trials.