The increasing legalization of cannabis for both medical and recreational use has created a complex public health challenge regarding its use during lactation. Tetrahydrocannabinol, or THC, is the primary psychoactive component found in the cannabis plant. When a lactating mother uses cannabis, THC enters her bloodstream and can transfer into her milk, raising concerns about potential exposure to the infant. Current scientific research is working to establish the extent and duration of this transfer, creating a clearer picture for healthcare providers and new parents.
The Mechanism of THC Transfer to Breast Milk
THC readily moves from the mother’s circulation into her mammary glands due to its chemical structure. The molecule is highly lipophilic, meaning it has a strong affinity for fat. Breast milk naturally has a high fat content, which acts as a reservoir where lipid-soluble compounds like THC can dissolve and accumulate.
Once in the bloodstream, THC binds to plasma proteins and rapidly redistributes into fatty tissues throughout the body, including the breast. THC concentrations are often higher in the milk than in the mother’s blood plasma, with some studies reporting a milk-to-plasma ratio as high as 8:1. This phenomenon contributes to the prolonged presence of the compound in the milk supply.
How Long THC Remains Detectable
The duration THC remains detectable in breast milk is highly variable and depends significantly on the mother’s pattern of use. Unlike alcohol, the elimination of THC is not rapid or predictable, largely due to its fat-soluble nature. For mothers who are chronic or heavy users, THC is stored in body fat and slowly released over an extended period.
Studies have shown that THC can be detected in breast milk for a range of timeframes, from a few days to several weeks after the last use. For women who use cannabis regularly, the estimated half-life of THC in breast milk can be quite long, sometimes averaging 17 days, meaning that detection could be possible for more than six weeks. Other studies on more acute use have estimated a shorter half-life of around 27 to 39 hours, suggesting clearance within two to eight days. This wide range highlights that there is no single, consistent time frame for clearance, making it impossible to recommend a specific “wait time” for breastfeeding.
Documented Developmental Effects on Infants
The primary concern regarding THC exposure via breast milk is the potential impact on the rapidly developing infant brain. THC acts on the endocannabinoid system, which plays a role in neurodevelopment, and the infant’s brain is highly sensitive during this period.
Research into the direct effects of THC exposure through lactation is limited and often complicated by the fact that many mothers who use cannabis while breastfeeding also used it during pregnancy. One study found that daily or near-daily maternal cannabis use was associated with decreased motor skill development at one year of age in breastfed infants. Specifically, this research noted a drop in the Bayley index of infant motor development scores compared to unexposed infants.
Infants exposed to THC through milk have also been reported to experience altered behaviors, such as lethargy, less frequent feeding, and shorter feeding times. While the estimated daily dose of THC ingested by an exclusively breastfed infant is often very small, the long-term neurobehavioral effects are still unclear. Because THC is stored in fatty tissue, infants exposed through milk may test positive in urine screens for two to three weeks, indicating systemic exposure. The inability to fully rule out long-term harm, especially concerning cognitive function and executive function, remains a significant limitation of current research.
Medical Recommendations and Safer Alternatives
Major public health organizations have issued guidance advising against cannabis use while lactating due to the unknown risks to the infant. Organizations like the American Academy of Pediatrics (AAP) and the Centers for Disease Control and Prevention (CDC) recommend that mothers abstain from using all cannabis products while breastfeeding. This recommendation is based on the uncertainty surrounding the long-term effects of THC on the developing brain.
The practice of “pumping and dumping,” which is sometimes effective for rapidly cleared substances like alcohol, is generally not useful for THC. Since THC is highly fat-soluble and slowly released from the mother’s body fat over days or weeks, discarding milk for a short period will not eliminate the compound from the milk supply.
For mothers who use cannabis to manage pain, anxiety, or stress, healthcare providers can suggest safer non-cannabis alternatives. These alternatives include evidence-based pharmacological treatments that have known safety profiles during lactation, as well as non-pharmacological interventions such as counseling, support groups, and cognitive behavioral therapy.