Human Milk Cannabinoid Concentrations and Associations with Maternal Factors: The Lactation and Cannabis (LAC) Study

Background and Objectives: As cannabis use increases among reproductive-aged women, there is a growing need to better understand the presence of cannabinoids in milk produced by women using cannabis. It is unclear how concentrations of cannabinoids such as delta-9-tetrahydrocannabinol (Δ⁹-THC) persist in milk after cannabis use and what factors contribute to variation in milk Δ⁹-THC concentrations. Our objectives were to measure cannabinoids in human milk following cannabis abstention, after single and repeated instances of cannabis use, and identify factors contributing to concentration variation. Methods: The Lactation and Cannabis (LAC) Study prospectively observed 20 breastfeeding participants who frequently used cannabis (≥1/week), had enrolled <6 months postpartum, were feeding their infant their milk ≥5 times/day, and were not using any illicit drugs. Participants collected a baseline milk sample after ≥12 hours of abstaining from cannabis and five milk samples at set intervals over 8-12 hours after initial cannabis use. Participants completed surveys and recorded self-directed cannabis use during the study period. Results: Δ⁹-THC peaked 120 minutes after a single instance of cannabis use (median, n = 9). More instances of cannabis use during the study period were associated with greater Δ⁹-THC area-under-the-curve concentrations (ρ = 0.65, p = 0.002), indicating Δ⁹-THC bioaccumulation in most participants. Baseline Δ⁹-THC logged concentration was positively associated with self-reported frequency of cannabis use (b = 0.57, p = 0.01). Conclusions: Cannabinoids are measurable in human milk following cannabis use, and concentrations remain elevated with repeated cannabis use over a day. Substantial variation in Δ⁹-THC milk concentrations reflects individual differences in characteristics and behavior, including average postpartum frequency of cannabis use.