Major League Baseball said Byrd tested positive for Tamoxifen, which can reduce side effects of steroid use and increase testosterone.
"I made an inexcusable mistake," Byrd said in a statement released by the players' association. "Several years ago, I had surgery for a condition that was private and unrelated to baseball. Last winter, I suffered a recurrence of that condition and I was provided with a medication that resulted in my positive test. Although that medication is on the banned list, I absolutely did not use it for performance enhancement reasons."
Blue Jays 9, Red Sox 6: Jose Bautista, Colby Rasmus and J.P. Arencibia hit two-run homers to lead visiting Toronto. David Ortiz had two home runs for Boston, his 37th multihomer game for the Red Sox, tying Ted Williams for the club record.
It was the fourth win in six games for Toronto, which overcame three errors and blew an early four-run lead.
Cardinals 8, Marlins 7: Rafael Furcal and pinch-hitting pitcher Joe Kelly drove in runs in the 10th inning for visiting St. Louis, which scored four runs in the top of the ninth, for its fourth straight victory.
Reds 3, Brewers 1: Mat Latos fanned a personal-best 13 in his second career complete game for host Cincinnati.
Padres 8, Astros 7: Carlos Quentin hit an RBI double in the 10th in Houston.-- AP