The invention relates to a method used for rapid detection of illegal additives in weight-reducing medicines, health care products, or foods, and specifically relates to a method used for determining whether a product, which is suspected to be mixed with sibutramine, contains sibutramine. The method comprises following steps: (1) an appropriate amount of the product is collected, is mixed with a special solvent, and an obtained mixture is subjected to shaking or ultrasonic assisted dissolving so as to obtain a mixed liquid; (2) specific electrochemical parameters of the mixed liquid are determined using an appropriate detector based on specific electrochemical principles; and (3) illegal addition of sibutramine of the product can be determined based on the value of the electrochemical parameters. According to the method, filtration of sample solution is not needed; time consuming of the whole detection processes ranges from 2 to 3min; the method is rapid, convenient, and safe, is high in sensitivity, and is friendly to the environment.