LONDON (Reuters) - Olympic 100 meters champion Justin Gatlin failed to have a four-year doping ban overturned by the Court of Arbitration for Sport (CAS) on Friday.

A U.S. arbitration panel suspended Gatlin in January for four years after he tested positive for the male sex hormone testosterone in 2006.

The 25-year-old American was also guilty of another doping offence in 2001 when he failed a drugs test because of medication for Attention Deficit Disorder, meaning a four-year ban was imposed.

Galin's failure to have the ban reduced to two years means he will not be able to compete in the U.S. Olympic trials and will miss the Beijing Games.

(Reporting by Martyn Herman, editing by Miles Evans)