When he runs out of these pills, Mr. Johnson said, he shuts himself inside his downtown apartment for days and communicates with no one until a new prescription becomes available. He said he was coming forward with his story so that his friends and family might better understand his situation, and also so that the National Football League might improve its handling of concussions.

While the league’s guidelines regarding head injuries have been strengthened over the past decade, the N.F.L.’s record of allowing half of players who sustain concussions to return to the same game remains a subject of medical debate.

“I am afraid of somebody else being the next Andre Waters,” said Mr. Johnson, who spent two weeks in February at a psychiatric hospital outside Boston with, he said, no appreciable results. “People are going to question me: ‘Are you a whistleblower, what are you doing this for?’ You can call it whatever you want about what happened to me. I didn’t know the long-term ramifications. You can say that my coach didn’t know the long-term, or else he wouldn’t have done it. It is going to be hard for me to believe that my trainer didn’t know the long-term ramifications, but I am doing this to protect the players from themselves.”

The N.F.L. spokesman Greg Aiello said that the league had no knowledge of Johnson’s specific situation. Regarding the subject of player concussions in general, he said, “We are very concerned about the issue of concussions, and we are going to continue to look hard at it and do everything possible to protect the health of our players.”

At a news conference yesterday in Miami, where the Super Bowl will be held Sunday, Gene Upshaw, the executive director of the National Football League Players Association, spoke in general terms about concussions in the N.F.L. “If a coach or anyone else is saying, ‘You don’t have a concussion, you get back in there,’ you don’t have to go, and you shouldn’t go,” Upshaw said, not speaking about the Johnson case specifically. “You know how you feel. That’s what we tried to do throughout the years, is take the coach out of the decision-making. It’s the medical people that have to decide.”

Mr. Johnson, who has a 2-year-old daughter and a 1-year-old son, is currently in divorce proceedings with his wife, Jackie, a situation that he admitted was compounding his depression.

He was arrested in July on domestic assault-and-battery charges, which were later dropped because his wife declined to testify. Mr. Johnson said that his concussive symptoms and drug addiction not only precipitated his marriage’s decline but began several years before it, specifically that preseason of 2002.