Cannabis, commonly known as marijuana, contains hundreds of chemical compounds, the most well-known being delta-9-tetrahydrocannabinol (THC). THC is the primary component responsible for the psychoactive effects experienced by users. As cannabis use becomes more widespread, nursing parents are seeking clear, evidence-based answers about its safety. This article addresses whether THC passes into breast milk and the implications for infant health.
Understanding THC Transfer into Milk
The chemical compounds in cannabis, particularly THC, transfer from a mother’s bloodstream into her breast milk. This transfer is a direct consequence of THC’s high lipophilicity, meaning it is fat-soluble. Because breast milk contains a relatively high amount of fat, it acts as a reservoir for compounds like THC.
THC’s high affinity for fat causes it to concentrate in the milk at levels significantly higher than in the mother’s blood plasma. Studies have calculated the milk-to-plasma ratio for THC to be around 6:1 to 8:1. This indicates that the concentration in breast milk can be several times greater than the concentration circulating in the mother’s blood. This concentration effect means the infant is exposed to a greater dose than expected based on maternal blood levels alone.
The timing of peak concentration in milk depends on the method of consumption. Following maternal inhalation of cannabis, the THC concentration in breast milk typically peaks approximately one hour after use. The challenge is not just the peak level, but the duration of its presence, which is prolonged because THC is stored in the body’s fat cells and released slowly.
Some studies have detected THC in breast milk for up to six days after use, while other research indicates components can persist for more than six weeks, especially with chronic use. This extended persistence means that even infrequent use can lead to prolonged infant exposure. The estimated daily infant dose of THC from breast milk is low (around 2.5% of the maternal weight-adjusted dose), but the long-term effects of this cumulative exposure on the developing brain remain a primary concern.
Documented Effects on Infant Development
Research into the effects of THC exposure via breast milk on infant development is limited, often relying on observational data. The main challenge in isolating these effects is that many mothers who use cannabis while nursing also used it during pregnancy. This prenatal exposure can confound the findings, making it difficult to attribute developmental changes solely to the postnatal exposure through milk.
Early studies have documented acute effects in exposed infants, including sedation, reduced muscle tone, and a diminished ability to suck effectively. These acute changes can interfere with successful breastfeeding and overall infant care. The long-term neurodevelopmental consequences are less clearly defined, as the research is still emerging. Furthermore, older studies often involved cohorts where the potency of cannabis products was lower than what is commonly available today.
Some long-term studies have pointed toward subtle impacts on motor development. One study found that infants exposed to cannabis during the first month of life showed a slight decrease in motor development scores at one year of age compared to unexposed infants. These findings suggest that the psychoactive compounds crossing into the milk may interfere with the rapid organization of the infant brain.
The primary worry centers on the developing central nervous system, which is highly sensitive to external chemical influences. THC interacts with the body’s endocannabinoid system, which plays a major role in brain development. Exposure during this window of rapid growth raises concerns about lasting effects on cognitive function, memory, and attention that may not become apparent until school age or adolescence.
Official Recommendations for Nursing Parents
Major medical and public health organizations universally recommend that nursing parents abstain from cannabis use during lactation. The Centers for Disease Control and Prevention (CDC), the American Academy of Pediatrics (AAP), and the American College of Obstetricians and Gynecologists (ACOG) advise against using marijuana, including products containing THC or cannabidiol (CBD), while breastfeeding.
This guidance reflects that no amount of cannabis has been proven safe for a developing infant, particularly given the unknown long-term risks to brain development. However, these organizations recognize the significant benefits of human milk. If a mother is unable or unwilling to stop using cannabis, she should be counseled on the known benefits of breastfeeding versus the potential risks of THC exposure.
A common misconception is that “pumping and dumping” can effectively clear THC from breast milk, similar to how it works for alcohol. However, this method is ineffective for cannabis. THC is stored in the mother’s body fat and slowly released into the bloodstream and milk over days or weeks. Discarding milk for a few hours will not eliminate the compound from the milk supply.
The only way to ensure an infant is not exposed to THC through breast milk is complete abstinence from cannabis use. Nursing parents should be aware that the increased potency of modern cannabis products means the potential risk to the infant may be greater than suggested by older studies.