Drug abuse by nursing mothers is an ongoing concern because it may cause many adverse effects to the newborns. The development of analytical methods to analyze drugs of abuse in colostrum (first milk produced after birth) has a huge importance, because it enables the monitoring and the correct follow-up to users and newborns. A liquid chromatography mass spectrometry (LC–MS) method was developed and validated for the determination of cocaine and smoked cocaine (crack) biomarkers in colostrum. Cocaine (COC) and its major metabolite benzoylecgonine (BZE), the pyrolytic products anhydroecgonine methyl ester (AEME) and anhydroecgonine (AEC) were analyzed after a simple protein precipitation procedure using atropine (ATP) as internal standard (IS). Applying a chemometric approach study, all peaks were chromatographically separated at isocratic condition with a Kinetex HILIC column for polar compounds, at 30 °C in 12 min. One ion was detected for the quantification and three ions for confirmation of each analyte. The method was linear for all analytes in the concentration range of 5–300 ng/mL with correlation coefficients (r) between 0.9983 and 0.9996. The lower limit of quantification (LLOQ) was 5 ng/mL with acceptable validation parameters. Matrix effect was assessed by post-extraction addition approach and showed good results, demonstrating that protein precipitation cleaning procedure is fast, reliable and demand small quantities of organic solvent. The LC–MS method is fast and cheap compared to other equipments and was also successfully applied to assess real samples of colostrum from nursing mothers who were suspect of cocaine/crack abuse.