A study of male college football players published in 2006 found a 22% increase in resting testosterone levels, from 20.0 to 24.4 nmol/L, after a 10-week resistance training program in the creatine supplemented group compared to placebo [REF].
One study done in 2008 showed that levels of insulin-like growth factor-1 (IGF-I) in muscle increased by 15% with creatine supplementation compared to placebo after 8 weeks of resistance training [REF].