He cannot play in the Bills' regular-season opener against the Chicago Bears, but may participate in the remainder of training camp and the preseason.
Bradham was charged with marijuana possession following a traffic stop last August. The NFL did not discipline Bradham at the time, but informed him in March that he faced a possible suspension.
"Everything was dismissed [in court]. Everything was dismissed. I'm not in the substance abuse program," Bradham said Wednesday. "It's kind of shocking and it's kind of disappointing that it came back again."
Bradham said the NFL declined an appeal of his suspension earlier this month.
Bills coach Doug Marrone said Bradham has matured since last season.
"I think last year Nigel struggled at times with us," Marrone said. "I saw a change, more of a commitment from him when we came back, which I give him a lot of credit for."
Bradham, 24, was a fourth-round pick of the Bills in 2012. He is the favorite to replace Kiko Alonso, who suffered a season-ending knee injury earlier this month.
He is eligible to participate in the remainder of training camp and the entire preseason.
Bradham recorded 51 tackles in 16 games last season, making two starts.