In the recent years, dietary supplements use among adults has increased dramatically to maintain good health and prevent diseases. Since some individuals find maintaining a balanced meal a challenge, they use dietary supplements to replace inadequate energy and micro/macro-nutrient intake. The aim of the study is to explore the use of dietary supplements and to assess awareness of its positive/adverse effects among physically active adults and the general population in Saudi Arabia. We conducted a cross-sectional online survey-based study and received 574 responses showing frequencies and types of dietary supplements. The results show that 44.6% of respondents use dietary supplements. The most used dietary supplements were Vitamin C and multivitamins, consumed by 44% of the respondents, Vitamin D (44%), Iron (41%), and Calcium (39%).  Protein sports bars and powder were consumed mainly by gym members, particularly those practicing weight-training exercises. Approximately 4% of respondents reported side-effects secondary to the usage of the dietary supplements. We conclude that the dietary supplement usage is widespread in Saudi Arabia among both gym members and the general public. It is highly recommended to increase awareness measures from official health entities by educating the general population and physically active adults about dietary supplement use and adverse effects to ensure safe practices.