(Reuters) - U.S. hammer thrower Gwen Berry has been stripped of her pending American record and suspended for three months for using a prohibited medication, the U.S. Anti-Doping Agency (USADA) said on Monday.

Berry, the favorite to win next month's U.S. Olympic trials, was suspended because she declared in March the use of an inhaler containing the banned substance Vilanterol Trifenatate, USADA said in a statement.

Although she subsequently tested negative for the substance at the U.S. indoor championships, a declared or admitted use of a prohibited substance constitutes an anti-doping violation, a USADA spokesman told Reuters.

She will be eligible to return to competition two days ahead of the U.S. Olympic trials, July 1-10 in Eugene, Oregon.

Her suspension began on March 29, the date USADA received her doping test results.

Berry, 26, was disqualified from all results subsequent to March 11, including her pending U.S. hammer throw record of 76.31 meters (250 feet, 4 inches) set in May in Arizona.

She could have received a longer suspension had it not been determined she was taking the medication in a therapeutic dose under the care of a physician and it was not being used to enhance her performance, USADA said.

(Reporting by Gene Cherry in Raleigh, North Carolina; Editing by Andrew Both)