Introduction : In recent years, the use of fitness supplements such as protein supplements, hormones, and hormone supporters has increased due to the increased interest of young people in fitness sports. Although fitness supplements have negative effects such as acne, skin rash, hair thinning, gynecomastia, changes in sexual function, testicular atrophy, aggressive behavior, and mood instability, in Mongolia, the lack of research data about prevalence of supplement use among fitness athletes and symptoms related to it has given us the reason to conduct study on this topic. Purpose: To study the prevalence of supplement use 72 and accompanying symptoms among people exercising in some fitness centers in Ulaanbaatar city. Materials and Methods : Using the analytical research snapshot model, we randomly selected 150 adult men who exercise in f itness centers such as California, Hawai, Golden gym, Ulaanbaatar, Powertec, and Agora located in Bayangol, Bayanzurkh, Sukhbaatar, and of Khan-Uul districts Ulaanbaatar. When collecting data from the participants, 3 groups filled out questionnaires with 15 questions, and statistical processing of the results was done using SPSS 20. Results: Of the respondents, 64% (N=96) used some form of fitness supplement (FS) and 36% (N=54) were non-users. Fitness supplement use varied by age, with younger people tending to use more fitness supplements. Men who exercised regularly every week were likely to use fitness supplements. Most of the men who used fitness supplements were professional athletes. In addition, the following changes related to its use are common among the group using the Phytess product. Include: Breast size increased in 47.9%, testicles became small in 30.2%, and decreased sexual function in 29.2%. In terms of other organ systems, 80.2% had adverse effects such as changes in body weight, and 39.6% had acne and rashes on the skin. In terms of mood, 34.4% were optimistic, 28.1% were depressed, and 22.9% showed signs of aggressiveness. Those with the highest frequency of symptoms were those who used anabolic hormones. Breast enlargement symptoms have been observed with the use of additional fitness products. Conclusions Most fitness enthusiasts use fitness supplements, and symptoms vary depending on the type