Cannabis and Breastfeeding: What the Evidence Says

Transfer of Cannabinoids into Breast Milk

• THC is highly lipophilic and transfers into breast milk at concentrations approximately eight times higher than maternal plasma levels
• A 2018 study published in Pediatrics detected THC in breast milk samples collected up to six days after the last maternal cannabis use
• CBD and other cannabinoids also transfer into breast milk, though at lower concentrations than THC; data on their infant safety are extremely limited
• Infant ingestion of THC through breast milk results in detectable levels in infant urine, confirming that exposure is pharmacologically significant

The transfer of cannabinoids — particularly THC — into breast milk is well-established and occurs at concentrations that are physiologically significant for a developing infant.

Potential Risks to the Breastfed Infant

• Infants have a highly immature cannabinoid receptor system and metabolise cannabinoids more slowly than adults, increasing exposure duration
• Case reports and small cohort studies link prenatal and postnatal THC exposure to impaired neurodevelopment, reduced motor development, and behavioural differences
• The developing brain’s endocannabinoid system is particularly vulnerable in the first months of life, coinciding with the standard breastfeeding period
• Long-term outcomes for infants exposed to cannabinoids through breast milk remain poorly characterised due to the absence of controlled clinical studies

Given the pharmacologically significant levels of THC in breast milk and the developmental sensitivity of the neonatal brain, the current evidence supports treating breastfeeding as a contraindication to any maternal cannabis use.

UK and International Guidance

• The Royal College of Midwives, NICE, and the American Academy of Pediatrics all advise women to stop cannabis use while breastfeeding
• There is no established safe level of THC exposure for breastfed infants, and the absence of proven harm at low doses is not the same as established safety
• Formula feeding is an option for women who require medical cannabis for serious conditions after careful risk-benefit discussion with their clinician
• Healthcare providers should counsel on cannabis and breastfeeding without judgement, recognising that many women use cannabis for legitimate medical reasons

The professional consensus across midwifery, paediatrics, and obstetrics is that breastfeeding and cannabis use — medical or otherwise — should not occur simultaneously.

Supporting Mothers Who Need Cannabis-Based Treatment

• Women with conditions that are effectively managed by cannabis should work with their prescribing clinician to identify the minimum necessary dose if they choose to continue breastfeeding
• Timing doses to minimise peak milk THC concentration (e.g., breastfeeding before rather than after taking cannabis) may reduce but does not eliminate infant exposure
• Alternative evidence-based treatments for the underlying condition should be explored thoroughly before a decision is made to continue cannabis while breastfeeding
• Peer support and non-judgemental clinical guidance are essential for mothers navigating this difficult decision, as stigma can prevent honest disclosure and appropriate care

Supporting mothers who need medical cannabis requires a compassionate, evidence-based conversation about risks and alternatives, with the infant’s neurological safety as the primary consideration.