MLB suspended New York Yankees slugger Alex Rodriguez, the game's highest-paid player, for 211 games. Another 12 players, including three All-Stars, were handed 50-game suspensions for their links to the Miami anti-aging clinic Biogenesis.
"Upon learning that players were linked to the use of performance-enhancing drugs, we vigorously pursued evidence that linked those individuals to violations of our program. We conducted a thorough, aggressive investigation guided by facts so that we could justly enforce our rules," Selig said.
"We pursued this matter because it was not only the right thing to do, but the only thing to do," he said.
Once seen as lax on steroids as fans embraced the increase in power displayed on the field, baseball has since become more aggressive than other U.S. professional sports leagues, in part because players discouraged their union from protecting drug users.
Baseball hired former U.S. Secret Service Director Mark Sullivan as part of its investigation into Biogenesis after the Miami New Times newspaper reported in January that some 20 players including Rodriguez had purchased banned substances from the clinic.
Selig called baseball's anti-doping "the best in all of professional sports," acknowledging the role of the Major League Players Association in implementing stricter penalties in recent years.
"This case resoundingly illustrates that the strength of our program is not limited only to testing. We continue to attack this issue on every front - from science and research, to education and awareness, to fact-finding and investigative skills," Selig said.
Baseball conducted 16,000 urine and blood tests on players in 2012, demonstrating that "the vast majority of our players ... play the game the right way," Selig said.