"I did take a banned substance, and for that I'm very sorry," Rodriguez said.
Rodriguez told Gammons that he felt an "enormous amount of pressure" when he arrived as a member of the Texas Rangers in 2001 after signing the largest contract in Major League Baseball history.
"Back then, [baseball] was a different culture. It was very loose. I was young, I was stupid, I was naive. I wanted to prove to everyone I was worth being one of the greatest players of all time.
He said he took the banned substances from 2001 to 2003 and has not taken any since.
"Since then I've proved to myself and to everyone that I don't need any of that," Rodriguez said.
Rodriguez was voted American League's Most Valuable Player in 2003, when he belted 47 home runs.
"I'm sorry for that time, I'm sorry for my fans," Rodriguez said today. "I'm guilty of being negligent and naive and not asking the right questions."
Rodriguez reportedly tested positive for the banned substances Primobolan and testosterone in 2003 while still with the Texas Ranger, a year before Major League Baseball implemented a program to suspend players who were found to be using performance enhancing drugs, according to a report from Sports Illustrated.
His sample, along with 103 other players who tested positive, could legally have been destroyed by the players union, but for reasons still unknown the samples were kept and later seized by federal investigators.
A-Rod Denied Steroid Use in 2007
Since Sports Illustrated broke the news this weekend that Rodriguez, 33, had tested positive for Primobolan and testosterone, he along with the players union and Major League Baseball had remained silent before speaking with Gammons Monday.
Soon after George Mitchell released a report on steroid use in baseball in 2007, which found that at least one player on every professional team in the major leagues had used performance-enhancing drugs, Rodriguez told CBS's Katie Couric in December 2007 that he had never used steroids.
"I've never felt overmatched on the baseball field. I've always been a very strong, dominant position. And I felt that if I did my work as I've done since I was, you know, a rookie back in Seattle, I didn't have a problem competing at any level. So, no," he replied then when asked if he had ever used steroids.
At spring training last year, Rodriguez again denied using steroids at a news conference, but in light of the recent allegations his comment carries an extra layer of intrigue.
"Last year, I got tested nine to 10 times," he said last year. "We have a very, very strict policy, and I think the game is making tremendous strides."
If Rodriguez had been tested that many times, he may have been subjected to additional tests, which would happen, for instance, if a player tests positive for a banned stimulant for the first time. A-Rod said later he was just exaggerating.
Baseball, America's once sacrosanct pastime, has been sullied by a series of steroids allegations and two of its biggest names in recent years. Barry Bonds and Roger Clemens are facing a perjury trial and perjury investigation, respectively, for lying about doping.
Bonds and Clemens allegedly lied about their use, though other players caught using steroids have taken the opposite tack. Jason Giambi confessed and Mark McGwire refused to discuss his past when questioned by a congressional committee.
Rodriguez is in the prime of his career and considered by some the best player in the league today. The slugger is seventh on the career list with 553 homers. Barry Bonds, mired in a steroids controversy of his own, is the career leader with 762 home runs.
In recent months he has made headlines for his off-the-field behavior, divorcing his wife to date pop superstar Madonna and being labeled "A-Fraud," for his perceived arrogance, by his former Yankees coach Joe Torre.
