Background/Objectives: Dietary supplement (DS) use has become increasingly prevalent among adult athletes worldwide and carries both potential benefits and risks. This study aimed to examine the prevalence and perspectives of DS use among adult athletes attending fitness centers in Saudi Arabia. Methods: A cross-sectional study was carried out between November and December 2024 using self-administered online questionnaires distributed through a convenience sampling method utilizing social media platforms. All adult athletes aged 18 and above currently residing in Saudi Arabia were included. Results: Results indicate that 73.9% of athletes use DS, primarily to address self-reported perceived vitamin/mineral deficiencies (62.0%) and to enhance energy availability (45.8%). The most frequently reported DS used by the responded were vitamins and minerals (77.3%), followed by fish oils (57.3%) and proteins (42.7%). The predominant adverse effects reported were changes in urine color (27.4%) and frequent urination (18.0%). Most supplements were consumed orally (78.4%), once daily (40.7%), or according to individual needs (26.7%), with dosage most often determined by a physician or pharmacist (35.1%). The mean perception score of DS effects on health outcomes was 3.69 ± 0.98, with a significant association with age (p = 0.041). Conclusions: This study highlights the increasing reliance on DS among athletes in Saudi Arabia, highlighting the need for public health interventions that promote safe and informed use of DS. While our study’s use of convenience sampling may limit their generalizability, the findings still provide important insights into current practices and perceptions. Future research should focus on regulatory measures and educational campaigns to mitigate risks and optimize benefits. Our results have significant implications for public health policy and practice.