High school athletes' practical knowledge on where to find and order third-party tested nutritional supplements increases after education when compared to a control group

To promote safe supplement use, athletes are advised to choose third-party tested (TPT) supplements to minimise doping risk. This study evaluated changes in knowledge on supplements in US high school athletes from a 2-week online supplement education programme. One group of sophomores (ED, n = 48) completed a Canvas course on safe supplement use, based on the Theory of Planned Behaviour, while the other group of freshmen (NOED, n = 38) did not. Participants completed questionnaires pre- and post-intervention to assess practical knowledge of finding and ordering TPT supplements, familiarity with World Anti-Doping Agency (WADA) banned substances and decision-making in supplement purchasing. Chi-Square and McNemar tests were applied with significance set at p ≤ 0.05. Pre-intervention no differences were found between groups (ages 14–17 years, 39.5% female) for any knowledge questions (p = 0.18). Post-intervention, ED participants were more likely to know where to find (58.3% vs. 39.5%, p = 0.041), and order (62.5% vs. 28.9%, p = 0.001) TPT supplements, and more athletes in ED (72.9%) than NOED (40.0%) reported deciding to purchase supplements themselves (p = 0.015). Parents were less influential in ED (75.0% vs. 92.1%, p = 0.019). Importantly, positive changes over time were larger for ED versus NOED in knowing where to find (28% vs. 13%, p = 0.04) and order (28% vs. 7%, p < 0.001) TPT supplements and WADA familiarity (19% vs. 5%, p = 0.01). Within-group changes showed ED improved on all practical knowledge questions (p = <0.001–0.008), whereas NOED only increased in knowing where to find TPT supplements (p = 0.003). These findings suggest an online educational programme may enhance practical knowledge of safe supplement use among high school athletes.