• Johann van der Merwe, Naomi E Brooks, and Kathryn H Myburgh.
• Department of Physiological Sciences, Stellenbosch University, Stellenbosch, South Africa.
• Clin J Sport Med. 2009 Sep 1; 19 (5): 399-404.

ObjectiveThis study investigated resting concentrations of selected androgens after 3 weeks of creatine supplementation in male rugby players. It was hypothesized that the ratio of dihydrotestosterone (DHT, a biologically more active androgen) to testosterone (T) would change with creatine supplementation.DesignDouble-blind placebo-controlled crossover study with a 6-week washout period.SettingRugby Institute in South Africa.ParticipantsCollege-aged rugby players (n = 20) volunteered for the study, which took place during the competitive season.InterventionsSubjects loaded with creatine (25 g/day creatine with 25 g/day glucose) or placebo (50 g/day glucose) for 7 days followed by 14 days of maintenance (5 g/day creatine with 25 g/day glucose or 30 g/day glucose placebo).Main Outcome MeasuresSerum T and DHT were measured and ratio calculated at baseline and after 7 days and 21 days of creatine supplementation (or placebo). Body composition measurements were taken at each time point.ResultsAfter 7 days of creatine loading, or a further 14 days of creatine maintenance dose, serum T levels did not change. However, levels of DHT increased by 56% after 7 days of creatine loading and remained 40% above baseline after 14 days maintenance (P < 0.001). The ratio of DHT:T also increased by 36% after 7 days creatine supplementation and remained elevated by 22% after the maintenance dose (P < 0.01).ConclusionsCreatine supplementation may, in part, act through an increased rate of conversion of T to DHT. Further investigation is warranted as a result of the high frequency of individuals using creatine supplementation and the long-term safety of alterations in circulating androgen composition. STATEMENT OF CLINICAL RELEVANCE: Although creatine is a widely used ergogenic aid, the mechanisms of action are incompletely understood, particularly in relation to dihydrotestosterone, and therefore the long-term clinical safety cannot be guaranteed.

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