A procedure is proposed for determining some narcotic and psychoactive substances (cathinones, tropane alkaloids, derivatives of ?-aminobutyric acid) in urine, including sample preparation and the determination of analytes by HPLC coupled with electrospray ionization tandem mass spectrometry. Sample preparation involved acid hydrolysis or the dilution of the sample. The lower limit of quantification is 200 pg/mL; the limit of detection is 100 pg/mL; and the calibration curves are linear in the range 0.2–50 ng/mL. The procedure was tested on real samples provided by the Toxicological Department of the Krasnodar Regional Narcological Dispensary. The high sensitivity of the analytical system ensures its use for the determination of narcotic preparations within a certain time after their intake, which may be of particular importance for forensic examinations.