Olympic hurdles gold medallist Dawn Harper-Nelson has been suspended for three months after testing positive for a banned substance.

The U.S. Anti-Doping Agency announced the sanction Tuesday.

USADA says the 32-year-old Harper-Nelson tested positive for the prohibited substance hydrochlorothiazide and related metabolites in an out-of-competition sample. She told USADA it was caused by blood pressure medication prescribed by a physician to treat hypertension.

In a statement posted on her Twitter account, Harper-Nelson said she has learned "a valuable lesson and hope my mistake will serve as a reminder to all athletes to be diligent in thoroughly checking any and all prescribed medications."

Her period of ineligibility started Dec. 1.

Harper-Nelson captured gold in the 100-metre hurdles at the 2008 Beijing Games. She earned silver four years later in London.