THC in Breast Milk: Facts, Risks, and Transfer

Cannabis use has become more common with increasing legalization and changing social attitudes. For breastfeeding parents, concerns remain about how tetrahydrocannabinol (THC) and other cannabinoids affect infants through breast milk. Understanding the risks is essential for informed decisions about cannabis consumption while nursing.

Research confirms that THC transfers into breast milk, but the extent of exposure and its effects on infant development are still being studied. With limited conclusive data, healthcare professionals often advise caution.

Key Cannabinoid Components in Human Milk

Human milk contains cannabinoids from external sources like cannabis and those produced by the body. These compounds interact with the endocannabinoid system, which influences neurological and physiological development. Among the cannabinoids detected in breast milk, tetrahydrocannabinol (THC), cannabidiol (CBD), and endogenous cannabinoids such as anandamide are of particular interest.

Tetrahydrocannabinol (THC)

THC, the main psychoactive compound in cannabis, has been detected in breast milk following maternal use. It is fat-soluble, accumulating in lipid-rich tissues, including mammary glands. A JAMA Pediatrics (2018) study found THC present in breast milk up to six days after last reported use, with concentrations varying based on frequency and quantity of cannabis consumed. Since THC binds to fat, it may persist longer in breast milk than substances that clear more rapidly from the bloodstream. Potential concerns include neurodevelopmental effects due to THC’s interaction with cannabinoid receptors involved in brain maturation.

Cannabidiol (CBD)

CBD, a non-psychoactive cannabis component, has also been identified in breast milk, though research on its transfer and effects is limited. Unlike THC, CBD does not cause intoxication but interacts with receptors influencing inflammation, pain perception, and mood regulation. A 2021 Frontiers in Pharmacology review noted that while CBD is less lipophilic than THC, it still has an affinity for fat-rich compartments, suggesting accumulation in breast milk. Data on exact concentrations transferred to nursing infants remain sparse. Some researchers hypothesize that CBD’s anti-inflammatory properties may have therapeutic potential, but without controlled studies on neonatal exposure, its safety is unclear. Additionally, unregulated CBD products may contain contaminants such as pesticides, heavy metals, or residual solvents, posing additional risks.

Endogenous Cannabinoids

Human milk naturally contains endocannabinoids, lipid-based neurotransmitters that regulate physiological processes. Anandamide (AEA) and 2-arachidonoylglycerol (2-AG) are the most studied, playing roles in appetite stimulation, immune modulation, and neurodevelopment. A European Journal of Pharmacology (2019) study found 2-AG present in significantly higher concentrations than AEA, suggesting its importance in early feeding behaviors. These naturally occurring cannabinoids interact with the infant’s endocannabinoid system, potentially influencing suckling responses and energy balance. How external cannabinoids like THC interfere with these natural mechanisms remains an area of ongoing investigation.

Pharmacokinetics in Nursing Parents

The pharmacokinetics of THC in nursing parents involves absorption, metabolism, distribution, and excretion. Following cannabis use, THC is rapidly absorbed into the bloodstream, with bioavailability varying by route of administration. Inhalation leads to peak plasma concentrations within minutes, whereas oral consumption results in delayed absorption due to first-pass metabolism in the liver. THC’s lipophilic nature allows it to integrate into adipose tissues, including mammary glands, where it can be sequestered and slowly released into breast milk.

Once in circulation, THC undergoes hepatic metabolism, primarily through cytochrome P450 enzymes, forming active and inactive metabolites. The primary metabolite, 11-hydroxy-THC (11-OH-THC), exhibits psychoactive properties, while 11-nor-9-carboxy-THC (THC-COOH) serves as a biomarker for cannabis exposure. The half-life of THC varies, influenced by frequency of use, body composition, and metabolism. Chronic users experience prolonged elimination due to accumulation in fat stores, leading to sustained low-level excretion into breast milk even after discontinuing cannabis use.

Studies using liquid chromatography-mass spectrometry (LC-MS) have detected THC concentrations in human milk ranging from 1 to 9 nanograms per milliliter, with variability based on maternal usage. A Clinical Pharmacology & Therapeutics (2020) study found THC levels in milk peak within one to two hours post-consumption and decline gradually, though measurable amounts persist for days. The milk-to-plasma ratio for THC is estimated at 0.2 to 0.8, suggesting preferential partitioning into breast milk relative to blood. This prolonged presence raises concerns about cumulative exposure in nursing infants, particularly given the immaturity of neonatal metabolic pathways responsible for cannabinoid clearance.

Routes of THC Transfer Into Breastmilk

THC’s transfer into breast milk is governed by physiological mechanisms. Its lipophilic nature enables movement across biological membranes, accumulating in lipid-rich tissues, including mammary glands. Unlike hydrophilic compounds that diffuse through aqueous channels, THC binds to milk’s fat content, leading to prolonged retention and gradual release.

Passive diffusion is the primary mechanism of THC transfer. As THC levels rise in maternal plasma, the compound moves into milk to reach equilibrium. Due to its fat affinity, THC does not distribute evenly in milk, with higher concentrations in fattier hindmilk compared to foremilk. This suggests the timing of breastfeeding in relation to cannabis use may impact infant exposure, though overall clearance remains slow due to THC’s sequestration in adipose tissue.

Enterohepatic recirculation further prolongs THC presence in breast milk. Once metabolized in the liver, some conjugated metabolites are excreted into bile and released into the gastrointestinal tract, where they can be reabsorbed into circulation. This recirculation effect is particularly relevant for chronic cannabis users, where repeated exposure leads to sustained low-level secretion into breast milk even after cessation.

Factors Influencing Cannabinoid Concentrations

THC concentration in breast milk varies due to biological and behavioral factors. Frequency and duration of cannabis use are significant determinants. Occasional users typically exhibit lower and more transient THC levels, while chronic consumers experience prolonged accumulation due to THC’s fat-soluble nature. Pharmacokinetic analyses show that daily cannabis users can retain detectable THC in milk for weeks after cessation, whereas infrequent users may clear it more rapidly.

Maternal metabolism and body composition also influence cannabinoid retention. Individuals with higher body fat percentages store THC longer, as adipose tissue serves as a reservoir. Enzymatic activity within the cytochrome P450 system affects THC metabolism and elimination, with genetic variations leading to inter-individual differences in cannabinoid processing.

Analytical Techniques for Detection

Detecting THC in breast milk requires highly sensitive analytical methods due to low concentrations and complex interactions with lipid-rich matrices. Conventional drug screening tests, such as immunoassays, lack the specificity and sensitivity needed for accurate quantification. Advanced techniques such as liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) are used in research and clinical settings.

LC-MS is particularly effective for analyzing biological fluids, detecting multiple cannabinoids and metabolites simultaneously. This method separates compounds based on chemical properties before ionizing them for mass spectrometric detection. Studies demonstrate LC-MS can identify THC concentrations as low as 1 nanogram per milliliter, making it one of the most reliable approaches for assessing exposure. GC-MS, while similarly effective, requires additional sample preparation, including derivatization to improve volatility.

Emerging techniques, such as ultra-high-performance liquid chromatography (UHPLC) coupled with tandem mass spectrometry, continue to refine detection capabilities, offering even greater sensitivity and accuracy in cannabinoid analysis.