In 2007 Koerts admitted to doping over a span of eleven years. In 1993 while at , he started taking testosterone under guidance from the team doctor. In 1997 at , he was encouraged to
microdose on
erythropoietin (EPO), but refused. However, in 1999, after being demoted to a lower level team he started to dope. He continued to dope occasionally until 2004. ==Post professional cycling==