Recent studies have announced that many food supplements for weight loss contained undeclared sibutramine. We have analysed 10 samples of herbal weight loss food supplements (FS) by HPLC/HRMS and UHPLC/MS-MS. We have established that two of the analysed samples contained sibutramine: respectively 5 μg/per capsule and 20 μg/per capsule. Illegal inclusion of this substance in FS could cause serious side effects and long term health consequences. The regulatory requirements for FS should be enhanced for more comprehensive consumers’ protection. The need for mandatory quality control of these products and public awareness is undeniable.