It's within baseball's rules.
And he's not alone.
Amphetamines are banned in baseball, but players can get therapeutic-use exemptions (TUEs), in which they show a medical need for the substance.
It sounds like a perfect loophole. Get a doctor to diagnosis you with attention-deficit disorder and write a prescription, and you can have your greenies.
But as Green tells it, the loophole isn't easily exploited.
"Greenies" have been banned in Major League Baseball since the 2006 season, and their use in the game predates steroids -- and was probably always more prevalent. Players who wouldn't go near steroids took amphetamines without a second thought; given the taxing nature of baseball's schedule, with only a few days off a month, early-morning arrivals in cities and day games after night games, they were considered a near necessity.
And MLB didn't test for stimulants until two years after instituting testing for other performance-enhancing drugs like steroids.
According to the MLB report issued in January, there were 106 TUEs granted for ADD in the 2008 season. And the increase in TUEs from 28 in 2006 to 103 in 2007 got the attention of Congress in its January 2008 steroids hearing.
Green, 30, said he has ADD and has had it "forever" -- since he was a kid growing up outside Atlanta.
"At school I could cram and stuff," he said. "I was fine. I always made good grades. So my mom said, 'Yeah, no problem.'
"Once I got into pro ball, what happens in pro ball is you play every day. So you end up zoning out too much, and if you zone out too much while you're playing, you're done."
So in 2003 Green got a prescription for Adderall. By 2005 he thought he had overcome his problem and stopped taking the drugs. But he hit just .183 after the All-Star break.
He wanted to go back on Adderall in 2006, but in the first year of amphetamine testing the red tape proved too difficut.
Now Green has to visit an MLB-approved doctor every spring training. That doctor even interviewed his family to verify the ADD. And the Adderall prescription has to be written by his team doctor. His TUE has to be renewed every year.
That prevents doctor-shopping and phony diagnoses.
The number of TUEs granted by MLB has drawn criticism, such as from anti-doping expert Gary Wadler to the New York Daily News.
"It seems to me as an internist, that's a disproportionate number of adults with ADD requiring stimulants - roughly 10 percent of the league. I've seen a lot of adults (as patients) and I can count on one hand the number of people I've seen with ADD," said Wadler, who is chairman of the World Anti-Doping Agency's Prohibited List and Methods Committee. "Since so many (players) received TUEs, it's crying out for close examination of the TUE process for baseball and how it stacks up against the international standard. I don't know that there's an epidemic of ADD in baseball."But as Green describes it, MLB makes it hard to fake ADD.
"It's a whole process you have to go through," he said. "They have to, to make it legitimate."
In fact, after Seattle called up Green from Triple-A in 2007, he tested positive for Adderall and he had to enlist the union's help in transferring his minor-league TUE to the major league testing program.
Adderall, according to the Web site of manufacturer Shire, is a "central nervous system stimulant" that includes as its ingredients amphetamine aspartate monohydrate and dextroamphetamine sulfate.
But Green said he doesn't feel taking one every day (he actually takes it only on days he plays) gives him an unfair advantage on the field.
"I've never taken greenies, so I don't know" if Adderall has the same effect, he said. "It helps me focus on the task at hand."
Asked if Adderall gives him extra energy, Green said, "I don't know. I still drink Red Bull and stuff."
He did say the Adderall can keep him up at night, which is why he takes it three hours before game time, since the effects are supposed to last eight hours.
Green has been a pleasant surprise for the Red Sox this year, making the team out of spring training as a non-roster player because Julio Lugo suffered a knee injury and winding up playing shortstop most of the time because of Lugo's ineffectiveness and Jed Lowrie's injuries.
Going into last night's game at Yankee Stadium, Green was batting .232 with five homers and 32 RBI.
"I think he's done a pretty good job," Boston manager Terry Francona said.
Green said he doesn't feel his TUE gives him an unfair advantage. He sees it as a medical necessity.
"I don't think what I take does the same as a greenie," he said.
And he's all for baseball's testing program.
"I think it's fair," he said. "The way I see it is you even out the playing field.
"I think it's a good program. It's tough to beat the system."