Tetrahydrocannabinol (THC) is the primary psychoactive compound in cannabis. As cannabis legalization and use become more widespread, many breastfeeding parents are asking whether this substance can pass into human milk and pose a risk to their infants. The growing potency of cannabis products today makes understanding the transfer and effects of THC during lactation an urgent public health concern. THC’s unique properties cause it to interact with the biological processes of the lactating body, leading to its presence in breast milk and subsequent exposure for the nursing baby.
How THC Transfers into Breast Milk
The mechanism by which THC moves from the mother’s bloodstream into breast milk is directly related to its chemical structure. THC is highly lipophilic, meaning it readily dissolves in fats and lipids, which are abundant in breast milk. This fat-soluble nature allows the compound to easily cross the membranes that separate the maternal blood from the milk ducts. Once the THC is in the milk, it tends to become concentrated there.
This concentration is quantified by the milk-to-plasma ratio, which compares the concentration of a substance in breast milk to the concentration in the mother’s blood plasma. Studies consistently report a median ratio around 7.0, indicating that the concentration in the milk is often several times higher than in the mother’s blood. The milk essentially acts as a reservoir, trapping the THC and its metabolites.
Documented Effects on the Nursing Infant
Research into the effects of THC exposure via breast milk on infants is limited, but existing studies raise concerns about the potential impact on neurodevelopment. The developing brain of a newborn is particularly vulnerable to psychoactive compounds like THC, which can interfere with the natural endocannabinoid system involved in brain development. The long-term consequences of this early exposure are not fully understood, but initial findings suggest possible developmental deficits.
One study suggested that exposure to THC through breast milk during the first month of life could be associated with decreased motor development at one year of age. A measurable decrease in the Bayley index of infant motor development was observed in exposed infants. Other observations have included altered behaviors, such as lethargy, reduced frequency of feeding, and shorter feeding times, which could affect the baby’s weight gain and overall nutrition.
It is difficult for researchers to isolate the direct effects of THC from breast milk exposure because many mothers who use cannabis during lactation also used it during pregnancy. Confounding factors, such as the use of other substances or differences in parenting behaviors, complicate the interpretation of infant outcomes. Despite these limitations, the theoretical risk of delivering a psychoactive substance to a developing brain remains a serious concern for health professionals.
Detection Windows and Clearance Time
The lipophilic nature of THC contributes to its prolonged clearance time from the body. Unlike substances that are cleared relatively quickly, THC is stored in the body’s fat tissue and is released slowly into the bloodstream over time. This slow release is why THC and its metabolites can be detected in breast milk long after the mother’s last use.
For chronic or heavy users, THC has been detected in breast milk for as long as six weeks following reported abstinence. The estimated half-life of THC in breast milk can range from 12 to 39 hours. This extended detection window makes the concept of “pumping and dumping” largely ineffective for clearing THC from the milk, unlike with alcohol. This prolonged presence means that a nursing infant could be exposed to THC for an unknown period, making it impossible to ensure a drug-free feeding timeline.
Current Guidance from Health Authorities
Major health organizations strongly advise against the use of cannabis in any form while breastfeeding due to the potential risks to the infant and the lack of long-term safety data. The American Academy of Pediatrics (AAP) and the American College of Obstetricians and Gynecologists (ACOG) recommend that women abstain from cannabis use during both pregnancy and lactation. This recommendation is based on the evidence that THC transfers into breast milk and the unknown consequences for the infant’s developing brain. The Centers for Disease Control and Prevention (CDC) also advises breastfeeding mothers to avoid marijuana or any marijuana-containing products, including those with CBD. Health authorities emphasize that there is no amount of cannabis proven safe to use during lactation, stressing that the safest choice for the infant is complete avoidance of marijuana.