The NFL and the union representing its players have agreed to a revised drug policy that includes Human Growth Hormone testing starting this season, the two sides said on Wednesday.

The formal agreement, which should see Human Growth Hormone testing begin by the end of the month, comes nearly a week after the players’ union agreed to terms for a new policy following a vote by player representatives.

A first violation of the performance enhancing drug policy, including Human Growth Hormone, will result in a suspension without pay of up to six games depending on the nature of the violation, the NFL and NFL Players Association said in a joint statement.

A positive test for diuretics or masking agents will result in a two-game ban while a positive test for a steroid, stimulant or Human Growth Hormone will result in a four-game ban. Evidence of an attempt to manipulate a test will result in a six-game ban.

A second violation of the steroid policy will result in a suspension without pay of 10 games while a third violation will result in banishment for a minimum of two years.

The NFL had struggled for years to reach an agreement with the union over Human Growth Hormone testing but it has finally done so, more than a year after Major League Baseball started testing, and long after many international sports began doing so.

The International Olympic Committee first started testing athletes for Human Growth Hormones at the 2004 Athens Olympics.

The NBA and NHL, North American’s two other major sports leagues, do not test for Human Growth Hormones but both have said they are considering it.

The NFL also tweaked policies regarding other drugs. Players who test positive for banned stimulants in the offseason no longer will be suspended but will be referred to the substance abuse program. Players who test positive for stimulants during the season will continue to be banned without pay for four games.

Appeals of positive performance enhancing drug tests will be heard by third-party arbitrators jointly selected by the NFL and the union.

The new rules mean that Denver Broncos receiver Wes Welker, Dallas Cowboys cornerback Orlando Scandrick and St. Louis Rams receiver Stedman Bailey are eligible to play this weekend. They have all been serving bans for positive stimulant tests.

Welker’s return comes in time for Denver’s Super Bowl rematch against the defending champion Seattle Seahawks.

Though the Broncos have started the season 2-0, they have missed Welker, who is the preferred target of quarterback Peyton Manning.

Scandrick and Bailey, meanwhile, could be on opposing teams when the Cowboys and Rams clash on Sunday.