This study aimed to investigate a miniaturized extraction methodology with analysis by GC-MS for simultaneous detection and quantification of cocaine (COC), benzoylecgonine (BZE) and cocaethylene (CE) in hair to monitor drug addicts. The process was done following the international guide of the Scientific Task Force on Forensic Toxicology. After sample extraction, derivatizing solution was added, clean-up was done by the Hollow Fiber Liquid Phase Microextraction (HF-LPME) and adapted to use the ultrasonic bath, a simple and easy-to-handle device. Isobutylchloroformate was first used as derivatization reagent to convert benzoylecgonine to isobutylbenzoylecgonine. Analytes quantification occurred within a linear range of 0.1 to 20 ng mg-1 for COC and 0.05 to 5 ng mg-1 for BZE and CE, with a correlation coefficient of r > 0.99. Limits of detection were 0.05; 0.03 and 0.03 ng mg-1, whereas limits of quantification were 0.1; 0.05 and 0.05 ng mg-1 for COC; BZE and CE, respectively. There was no matrix effect interference. Intra and inter-day precision and accuracy were acceptable according to international guidelines. The analytical method HF-LPME-GC-MS was successfully applied to 14 hair samples from patients admitted in drugs detoxification programs. All samples resulted positive for cocaine (0.80-> 20 ng mg-1) and benzoylecgonine (0.20-> 5 ng mg-1), 11 samples were positive for cocaethylene (0.10-> 0.60 ng mg-1).