In the global obesity pandemic, the demand for healthy products that provide weight loss is increasing. However, undeclared adulterants are commonly added to increase their performance and the development of rapid methods for detecting these compounds is fundamentally important. In this work, it was demonstrated that an electrochemical technique (square wave voltammetry) using boron-doped diamond (BDD) as the working electrode can be used for rapid screening and quantification of the doping substance fluoxetine (FLU) in samples like thermogenic supplements, compounded drugs, and weight loss herbal medicines. Fast screening of FLU is possible after easy sample dilution in a supporting electrolyte solution (0.1 mol L-1 H2SO4). In addition to the simplicity and low cost of the proposed method, adequate analytical characteristics in terms of limits of detection (0.1 mg L-1), linear range (1 to 50 mg L-1; r = 0.993), and recovery values (104 ± 6 %) were obtained. These results suggest that the method has great potential as a simple and fast screening test to detect FLU in natural products for anti-obesity therapy.