Jacobs was with Colorado Springs and was leading the team in games played (117), homers (23), doubles (30) and RBIs (97). He signed with the Rockies as a free agent last December.
"A few weeks ago, in an attempt to overcome knee and back problems, I made the terrible decision to take HGH," Jacobs said in a statement released by his representative. "I immediately stopped a couple of days later after being tested. Taking it was one of the worst decisions I could have ever made, one for which I take full responsibility.
"I apologize to my family, friends, the Colorado Rockies organization, Major League Baseball and to the fans. Now, as required by the Minor League drug program, I will serve a 50-game suspension. After my suspension is completed, I hope to have the opportunity to continue my career in the game that I love so much."
The Rockies were within their rights to release Jacobs because he was in the Minor Leagues, MLB's top labor official said on Thursday.
The Major League Joint Drug Agreement, which is collectively bargained with the Players Association, stipulates that a player cannot be released during the course of suspension for the use of a performance-enhancing drug, but the Minor League drug policy was unilaterally implemented by baseball.
"The rules are different," Rob Manfred, MLB executive vice president of labor relations and human resources, said after the owners' quarterly meetings in Cooperstown, N.Y. "[Jacobs] had a one-year contract and the 50-game suspension will take him to the end of the year. A release would not be allowed in the Major Leagues."
Dick Monfort, the Rockies' owner and chief executive officer, told reporters that Jacobs was placed on immediate leave on Saturday, after the club was notified about the positive test.
"I'm very disappointed," Monfort said. "That's something we preach very hard. Mike didn't come up through our system. He was a guy we invited to come to camp. He's actually played pretty well."
Jacobs made his Major League debut with the Mets in 2005, hitting 11 home runs in 100 at-bats. He was traded to the Marlins and spent three seasons with them, hitting 32 home runs in 2008. He played for the Royals in 2009 and returned to the Mets last season and played in seven games before being traded to Toronto.
He is a career .253 hitter with 100 home runs, 115 doubles and 310 RBIs in 556 Major League games.
The Rockies issued the following statement:
"We were very disappointed to learn that Mike Jacobs had been suspended after testing positive for a performance-enhancing substance.
"The Colorado Rockies have long been committed to eliminating the use of performance-enhancing substances from the game of baseball. We have fully supported the adoption and implementation of the Major League Baseball and the Major League Baseball Players Association Joint Drug Prevention and Treatment Program.
"We have routinely educated all of our players about the dangers of performance-enhancing substances and strongly encourage all players to avoid their use. We strongly believe that baseball and all other sports must continue to directly address the issue of performance-enhancing substances. There is no place in baseball for such substances, and we have and will continue to do what we can to eliminate them from our game."
Commissioner Bud Selig, who implemented the testing in the Minor Leagues in July 2010, addressed the suspension after the owners meetings.
"My reaction is that we have a program in place and it did what it was supposed to do," Selig said. "We don't duck the issue. We don't avoid the issue. This is a dramatic manifestation of that."
Manfred said MLB has made a proposal for blood testing for HGH to the MLB Players Association during their ongoing talks over a new collective bargaining agreement.
HGH is banned by MLB but blood testing is currently not sanctioned for players on the 40-man roster of each big-league team and the union has heretofore opposed it.
"It's an area where all the sports have the same problems and the same issue," Manfred said. "We've made a proposal on blood testing for HGH and we'll see how it turns out at the table. I can't say much more about it than that."
Travis Tygart, chief executive officer of the U.S. Anti-Doping Agency, praised baseball's position on HGH at the Minor League level.
"All those that value clean sport know that HGH testing is a necessary part of an effective anti-doping program; otherwise you give athletes a license to use this potent performance-enhancing drug with impunity," Tygart told AP. "This case demonstrates how MLB has stepped up to the plate and implemented HGH testing in the Minor Leagues to protect clean athletes and the integrity of competition."