For athletes

Supplements for athletes: what do the IOC and AIS distinguish?

The IOC consensus separates four purposes: managing micronutrient deficiencies, providing energy and macronutrients in a convenient form, a direct contribution to performance, and an indirect contribution that supports intense training. The text states that a complete nutrition assessment should be done before supplement decisions and that performance-enhancing products should be tried in training or a similar setting before being used in competition. ^[1]

The Australian Institute of Sport (AIS) divides products into four groups by level of evidence, safety and permitted status. Group A comprises products with strong scientific evidence for use in specific situations with evidence-based protocols; Group C comprises products for which scientific evidence does not support a benefit for athletes or no guiding research exists; Group D comprises products carrying a high contamination risk with prohibited substances or substances that may cause a positive doping test. ^{[2] [3] [4]}

The AIS classification is one organization’s program; the pages are updated over time and products can move between groups (the Group C page notes that products formerly in B were moved to C). ^[3]

What does the evidence say about the Group A performance supplements?

Caffeine. The ISSN 2021 statement reports that caffeine consistently improved exercise performance in studies where it was taken at 3–6 mg/kg body weight, that the minimum effective amount may be as low as 2 mg/kg, and that very high amounts such as 9 mg/kg were associated with a high rate of side effects; the most commonly used timing in studies is 60 minutes before exercise. ^[5] These are study protocols, not personal recommendations.

Creatine. The ISSN 2017 statement reports that creatine monohydrate increases muscle creatine and supports training adaptations in high-intensity repetitive exercise. ^[6] The IOC characterizes creatine’s effect as marginal gains and notes that a body weight increase of about 1–2 kg after loading (mostly due to water retention) could be a disadvantage in endurance or weight-bearing sports. ^[1] Details are in the creatine guide.

Beta-alanine. The ISSN 2015 statement reports that 4–6 g/day of beta-alanine for four weeks increased muscle carnosine, that the performance gain was more pronounced in open-ended tasks lasting 1–4 minutes, and that the only reported side effect was paresthesia (tingling). ^[7] The IOC lists caffeine, creatine, nitrate and sodium bicarbonate as supplements with enough support to provide marginal gains and adds beta-alanine to the list with the qualifier “possibly.” ^[1]

Sodium bicarbonate. The ISSN 2021 statement reports that 0.2–0.5 g/kg of bicarbonate improved performance in activities requiring muscular endurance, in combat sports and in high-intensity cycling, running, swimming and rowing tasks; the effect is best demonstrated in high-intensity tasks lasting between 30 seconds and 12 minutes. According to the text, higher amounts such as 0.4–0.5 g/kg in single-dose protocols give no additional benefit and are associated with more frequent, more severe side effects. ^[8]

Nitrate and glycerol. The IOC reports that dietary nitrate is among the evidence-based supplements and has been associated with a 1–3% improvement in sport-specific time trials shorter than 40 minutes. ^[1] Glycerol appears on the AIS Group A list as a performance supplement. ^[2]

Protein, BCAA and “testosterone boosters”

The AIS lists isolated protein supplements among Group A sports foods. ^[2] The evidence on when and how much protein powder is used is covered in the protein powder guide. BCAA and HMB are on the AIS Group C page; the page shows the current classification for BCAA, HMB, phosphate and tyrosine as B and the agreed classification as C. ^[3] “Testosterone boosters” such as Tribulus terrestris are in Group D; the AIS states that they are not on the WADA list but are frequently found in multi-ingredient products containing prohibited substances or carry a contamination risk. ^[4]

Doping risk: why do supplements pose a problem?

The IOC reports that inadvertent intake of prohibited substances not listed on the label is a known risk with supplements, and that the substances found come from many sections of the WADA list, such as stimulants, anabolic agents, selective androgen receptor modulators, diuretics, anorectics and β2 agonists. According to the text, even contamination at very low amounts can produce a positive doping result: adding only 2.5 µg of 19-norandrostenedione, a nandrolone precursor, to a supplement can exceed the urinary threshold (2 ng/mL) for 19-norandrosterone. ^[1]

In the international study of Geyer and colleagues, 634 non-hormonal supplements were bought from 215 suppliers in 13 countries between October 2000 and November 2001; 94 (14.8%) contained an anabolic androgenic steroid not declared on the label, and reliable data could not be obtained for 66 samples (10.4%). The positive rate was 21.1% among 289 products from companies that sell prohormones and 9.6% among those from companies that do not. ^[9] The sample dates from two decades ago; it cannot be read as the rate in today’s market.

Third-party programs aim to reduce the risk. The IOC states that third-party audits help identify products athletes can consider “low risk” but that no product can be guaranteed to be completely safe. ^[1] The Cologne List describes itself as an international quality management program based on independent product controls to reduce the risk of prohibited substances; it states that a product on the list also cannot be considered completely free of prohibited substances, because no laboratory can test all substances on the WADA list. ^[10] The program’s statement that “supplements do not go through an official approval process” is a general framework; in Türkiye, dietary supplements are subject to Ministry approval before marketing, but this approval is not a doping screen (Supplement regulation in Türkiye). Batch-based testing programs such as Informed Sport are used for the same purpose; these programs are a certification tool, not a product recommendation. WADA’s 2026 Prohibited List came into force on 1 January 2026. ^[11]

According to the Dopingle Mücadele Derneği’s (Anti-Doping Association) own statement, the association was authorized as Türkiye’s national anti-doping organization (NADO) under the Anti-Doping Authority and Cooperation Protocol signed with the Ministry of Youth and Sports on 25 May 2026. ^[12] Because information on the national organization can change, the current situation is followed from the announcements of the association and the Ministry of Youth and Sports. The legal framework of supplements in Türkiye is explained in a separate guide.

Adolescent athletes and supplements

The AAP’s 2016 report states that performance-enhancing substances are widely used among children and adolescents, that concerns about legal supplements cover high rates of product contamination, an association with later anabolic androgenic steroid use, and negative effects on the focus and experience of youth sport; it writes that for most young athletes these substances provide no meaningful benefit beyond the gains from maturation that comes with puberty and from appropriate nutrition and training. ^[13] ISSN, by contrast, interprets the “not for use under 18” warnings on creatine labels as a legal precaution and argues that creatine is acceptable for young athletes who are supervised, eat a balanced diet, know how to use it and do not exceed recommended amounts; this is the view of a sports nutrition society. ^[6] The two texts answer different questions (general use of performance-enhancing substances versus a single supplement).

RED-S and nutrition first

The IOC defines RED-S as a syndrome caused by relative energy deficiency, covering impairments in metabolic rate, menstrual function, bone health, immunity, protein synthesis and cardiovascular health; the etiological factor is low energy availability. ^[14] In this situation, a supplement does not replace inadequate energy intake; the IOC treats a nutrition assessment before supplementation as a prerequisite. ^[1] Athlete-specific supplement decisions are read together with the principles in the guide do you need supplements; product information is covered in the guide how to read a label and general safety in the guide are supplements safe. Combined use of supplements with medicines is on the drug interactions page; for the basic definition, the page what are supplements can be consulted.

This guide does not recommend personal doses. For athletes subject to doping control, product questions are referred to the national organization and a sports physician; for athletes who use medicines or are under 18, to a physician.