The NFL Players Association has agreed to a proposal regarding the league's drug policy, according to a report.

The new agreement will see the threshold for positive marijuana tests rise, and the use of amphetamines during the off-season will now change from the performance-enhancing stipulation to the substance of abuse policy.

The proposal will also bring in human growth hormone testing for the first time this season, although blood specimens will not be allowed to be taken on gameday, reports NFL Network.

"This is an historic moment for our players and our league," NFLPA President Eric Winston said in a statement.

"We have collectively bargained drug policies that will keep the game clean and safe, but also provide our players with an unprecedented level of fairness and transparency. Players should be proud of their union for standing up for what was best for the game."

The new rules could see several suspended players return to action when the proposal is finalised between the NFLPA and the NFL, which could be as early as next week.