evidence: The concentration of cannabinoids within milk varies with the time postpartum. During early lactation, drugs and proteins move easily from the blood into the milk through gaps between loosely packed epithelial cells. These gaps eventually narrow and utilize facilitated or passive diffusion to transfer molecules. [...] PPARγ expression rises in mammary tissue during lactation, thereby increasing lipid metabolism. The endocannabinoid AEA stimulates CB1R and PPARγ, ultimately increasing lipoprotein lipase activity. Prior research suggests that cannabinoids change human milk composition; however, no in vivo or clinical studies have corroborated this report. [...] Cannabis use leads to the presence of cannabinoids in human milk, which may contribute to their long-term accumulation and inhibit milk production. Cannabis use may also alter breast milk composition through its effects on lipid metabolism.