Background: Nutritional supplements and hormones are used at a high rate throughout the world. Objectives: to evaluate the prevalence of use of dietary supplement and hormones among gym attendees, and to assess participants' knowledge and attitude towards them. Methods: A cross-sectional study was done on 338 gym attendees in Taif city. A self-administered questionnaire was used. It included items on their sociodemographic characters, their exercise history, and their use of any nutritional supplements or hormones. Results: About 30% of the participants (29.6%) used nutritional supplements or hormones, and the most commonly used were protein powder (22.5%) and vitamins (13.6%). Among them, 11.2% agreed on hypertension, 28.7% agreed on liver disease, 35.5% agreed on weight gain, and 40.2% agreed on kidney disease as a side effect of supplements. For hormones, 21.3% agreed on hypertension, 22.2% agreed on diabetes mellitus, 39.1% agreed on weight gain, and 21.1% agreed on vision problems as a side effect of their use. Of the participants, 35.8% agreed that psychiatric problems are side effects, 25.4% agreed on testicular hypotrophy, and 37.9% agreed on breast enlargement. A non-significant relationship was found between the participants' level of education and both their use of any nutritional supplements or hormones, and source of information, and the majority of those who were not using nutritional supplements or hormones (79.5%) were not using a special diet. Conclusion: All gyms attendees should consult a healthcare professional before the use of hormones or nutritional supplements, and gym coaches should be educated regarding hormones and nutritional supplements.