Ramirez, who signed a two-year, $45 million contract with the Dodgers before the season, was hitting .348 with six homers and 20 runs batted in.
The suspension begins with Thursday's home game against Washington and he is eligible to return on July 3 against the Padres in San Diego. Ramirez, who is making $25 million this year, stands to lose about $7.7 million in salary.
The 36-year-old power-hitting outfielder had helped the National League Dodgers post a 21-8 record this season, the best mark in the major leagues, including an MLB record 13 successive home wins to start a season.
A 12-times All-Star player who came to the Dodgers last season by trade from the Boston Red Sox, Ramirez became the biggest name to be penalized since MLB began a testing program to detect use of performance-enhancing drugs in 2003.
His 533 career homers puts him 17th on the all-time list.
Ramirez issued a statement through the Major League Baseball Players Association, which said he had waived his right to appeal against the suspension.
"Recently I saw a physician for a personal health issue. He gave me a medication, not a steroid, which he thought was okay to give me," Ramirez said.
"Unfortunately, the medication was banned under our drug policy. Under the policy that mistake is now my responsibility. I have been advised not to say anything more for now. I do want to say one other thing; I've taken and passed about 15 drug tests over the past five seasons.
"I want to apologize to (Dodgers owner) Mr. McCourt, Mrs. McCourt, (manager) Mr. Torre, my team mates, the Dodger organization, and to the Dodger fans.
"LA is a special place to me and I know everybody is disappointed. So am I. I'm sorry about this whole situation."
Los Angeles Dodgers CEO Jamie McCourt responded to the news with a statement.
"We share the disappointment felt by our fans, our players, and every member of our organization. We support the policies of Major League Baseball, and we will welcome Manny back upon his return."
The suspension of Ramirez is the second doping shock to hit baseball in 2009.
Controversial Behavior
In February, New York Yankees third baseman Alex Rodriguez, baseball's highest paid player on a 10-year, $275 million deal, admitted he had used steroids during his three years with the Texas Rangers.
Dominican-born Ramirez, who grew up in New York City, has been one of been one of baseball's most colorful players in a career that began with the Cleveland Indians in 1993.
While in Boston, with whom he won World Series MVP honors in 2004, fans shrugged off the often controversial behavior of the dreadlocked outfielder as "Manny being Manny."
Dodgers third base coach Larry Bowa said Ramirez had been a positive force beyond his own hitting, helping the team's younger players.
"The way he's got these kids believing in themselves, I think he'll be welcomed back with open arms," Bowa told ESPN Radio about how his team mates were likely to react.
Bowa said that Ramirez had grown into a team leader.
"Without a doubt. Big time, in his own way. Having little meetings with guys in the clubhouse or in the dugout. He's always talking baseball, talking about what pitchers are trying to do, what to look for in certain situations.
"He's going to be missed, no question about that when you take a force like that out of your lineup."
