Pettitte said he tried HGH on two occasions, stressing he did it to heal faster and not enhance his performance. He emphasized he never used steroids.
"If what I did was an error in judgment on my part, I apologize," Pettitte said Saturday in a statement released by his agent. "I accept responsibility for those two days."
CBS correspondent Michelle Miller reports Pettitte emphatically denies the use of steroids or any other drugs. In a statement released Saturday night, the New York Yankees said "we support his coming forward."
On Thursday, Pettitte was among 85 players named by former Senate Majority Leader George Mitchell's investigation into steroids and performance-enhancing drugs. Pettitte had not commented publicly on the allegations.
Pettitte asked the trainer he shared with Roger Clemens, Brian McNamee, to help him with HGH while on the disabled list early in the season, the report said. McNamee recalled injecting Pettitte two to four times, Mitchell said.
"In 2002 I was injured. I had heard that human growth hormone could promote faster healing for my elbow," Pettitte said in the statement released to The Associated Press by agent Randy Hendricks.
"I felt an obligation to get back to my team as soon as possible. For this reason, and only this reason, for two days I tried human growth hormone. Though it was not against baseball rules, I was not comfortable with what I was doing, so I stopped.
Pettitte was not linked to steroids in the report, and said he never had never used them.
"I have the utmost respect for baseball and have always tried to live my life in a way that would be honorable," he said. "If I have let down people that care about me, I am sorry, but I hope that you will listen to me carefully and understand that two days of perhaps bad judgment should not ruin a lifetime of hard work and dedication.
"I have tried to do things the right way my entire life, and, again, ask that you put those two days in the proper context. People that know me will know that what I say is true," he said.
According to CBS News' chief investigative correspondent Armen Keteyian, the extent of drug use revealed in the report calls for what may prove to be a daunting task: finding some way to detect the new drug of choice in sport - not steroids, but Human Growth Hormone, or HGH, craved by athletes driven to enhance performance and avoid positive drug tests.
The 35-year-old lefty is 201-113 lifetime. He started his major league career in 1995 and won four World Series championships with the Yankees. He pitched for his hometown Houston Astros from 2004-06 and helped them reach their first World Series.
Pettitte returned to the Yankees last season and went 15-9. This month, he put off retirement and agreed to a $16 million, one-year contract to play for the Yankees next season.
Mitchell devoted 1½ pages to McNamee's testimony about Pettitte. Clemens was mentioned on nearly nine pages, with McNamee saying he injected the star pitcher.
Clemens was accused of using steroids and HGH and, through his lawyer, vehemently denied the accusations.
When Clemens joined the Yankees in 1999, he and Pettitte became fast friends and training partners. McNamee was part of their regimen - Clemens had worked with him in Toronto before being traded to New York.
According to the Mitchell Report, Pettitte asked McNamee about using HGH after the 2001 season, and the trainer said he discouraged the pitcher from trying it.