Sibutramine, a drug for weight loss, has been implicated in numerous deaths in recent years and has been sold to the public in adulterated herbal slimming supplements. In order to efficiently detect and verify the existence of sibutramine in samples, it was essential to develop a mass spectrometry method for detecting sibutramine, the drug described in this study. Sibutramine was extracted from herbal material matrixes by sonication. Separation was achieved via liquid chromatography and mass spectrometry analysis was conducted by electrospray ionization triple‐quadrupole mass spectrometry in the multiple reaction monitoring mode (MRM). The main fragmentation pathways were proposed and verified by Isotopic labeling of sibutramine hydrochloride. These pathways involved the rearrangement of hydrogen, methyl migration and an unstable multi‐membered‐ring transition structure. We found four high‐abundance fragment ions and created a method to verify the presence of sibutramine in herbal slimming supplements using MRM. This verification method offers high quality data with high sensitivity, low limits of detection and clear, easily interpretable results that are well suited for the verification of sibutramine hydrochloride in herbal slimming supplements of complex mixtures.