Major League Baseball drew praise from anti-doping advocates Tuesday when it announced it would become the nation's first professional league to test for human growth hormone.
Under the league's new five-year labor agreement, players must submit to random blood tests for HGH -- a naturally occurring substance used by some athletes to build muscle mass and speed the recovery from injury.
"I think it sends an important message that Major League Baseball doesn't accept athletes using HGH," said Dr. Andrew Gregory, an assistant professor of orthopedic surgery and rehabilitation at Vanderbilt University Medical Center. "If it's illegal and the pros aren't doing it, kids will see that."
HGH can be obtained legally only with a prescription.
Under the agreement, which still has to be ratified by both sides, ballplayers who test positive in the off-season or during spring training will be suspended for 50 games -- the same punishment doled out to steroid abusers. There is no agreement yet on in-season testing.
The announcement was applauded by the World Anti-Doping Agency as a positive development in the fight against doping in sports.
"MLB has shown leadership by becoming the first of the major professional sports in North America to accept that it needs to protect both its athletes and its sport by introducing HGH testing," agency president John Fahey said in a statement. "We need as much blood sampling conducted for HGH as possible, and MLB has set an example for the other major sports to follow."
The National Football League announced a similar screening program in August, but players have yet to agree to the testing and appeals process.
Because it's a natural compound, HGH is harder to detect than other performance-enhancing drugs like steroids. But a blood test introduced at the 2004 Summer Olympics in Athens homes in on subtle differences between the body's own hormone and the injectable version.
Produced by the pea-size pituitary gland deep inside the brain, HGH stimulates the growth of muscles, bones and organs during development. Some children require a prescription for HGH if their bodies produce too little.
But in adulthood, hormone production usually tapers off, preventing dangerous overgrowth of the heart, liver and other organs. Too much HGH in adulthood has been linked to diabetes, high blood pressure, joint swelling and nerve pain. But some athletes seek out HGH despite the risks.
"People are willing to accept pretty major side effects to get the results they're looking for," said Gregory.
And when they obtain it illegally, athletes risk injecting something other than HGH.
"There's the danger you're getting an impure product because you're not getting it from a pharmacy," said Gregory. "I have had high school athletes and parents ask me about using HGH to get bigger and taller because they want to get to the next level in their sport. Of course, I don't give it to them. But that doesn't mean they're not getting it somewhere else."
Blood-testing for HGH is more expensive and more invasive than urine testing for steroids, making it hard for high schools, colleges and minor leagues to set up. However, Minor League Baseball started testing for HGH in 2010.
The MLB agreement does not yet include HGH testing during the regular season and playoffs, leaving open a dangerous loophole, said Gregory.
"For drug testing to be effective, you have to be able to test anybody, anywhere, any time," said Gregory. "If you can't test during regular season, players will easily work around that."
The league said it would explore in-season testing cautiously, after ensuring it doesn't interfere with players' health and safety.
The Associated Press contributed to this story.