Breast milk is widely recognized as the primary source of nourishment for newborns, making it an unparalleled and indispensable provider of essential nutrients, microbiological components, immunological factors, and energy content. To investigate this further, a cohort comprising 254 breastfeeding women participated in interviews, and milk samples were aseptically collected for subsequent analysis involving bromatological, microbiological, and clinical analysis. The investigation focused on the identification of specific microorganisms in breast milk and their susceptibility to the exposure of toxic substances and controlled medications. Notably, this study places particular emphasis on the significant decline in lactic acid bacteria observed in breast milk when influenced by substances such as cocaine, cannabis, crystal, and morphine. These detrimental agents have been found to adversely affect the growth of microorganisms within breast milk. On the contrary, the outcomes of this study indicate that the utilization of toxic substances does not exert a noteworthy impact on the nutritional quality of breast milk.