Adulteration of botanical food supplements with undeclared synthetic drugs is a common problem. One of the most affected product groups are the slimming agents. There are no analytical protocols for the detection of synthetic adulterants from these products. The present study aimed at the development of a multistep analytical method for the quick and reliable determination of sibutramine, one of the most common adulterants among botanical food supplements. The extract of a sibutramine-containing slimming formula was analysed by colour tests, TLC, HPLC-DAD, MS and NMR. The multistep method proposed by the authors allows the quick identification of sibutramine in counterfeit samples in laboratories with different instrumentation.