In the latest lawsuit based on medical issues against the N.F.L., a dozen former players have accused the league and its teams of repeatedly administering the painkiller Toradol before and during games, worsening high-risk injuries like concussions.
The players also contend that the league and its teams failed to warn them of the consequences of taking the drug, a blood thinner that, according to the suit, "can prevent the feeling of injury" and therefore made it harder for players to recognize when they had concussions.
"The plaintiffs have described the situation as one of being in a pregame locker room with players lining up to receive injections of Toradol in a 'cattle call' with no warnings of any sort being given, no distinguishing between different medical conditions of the players, and regardless of whether the player had an injury of any kind," the suit alleges.
The dozen retired players, including Joe Horn, Matt Joyce and Jerome Pathon, played in the late 1990s and early 2000s and say they now have anxiety, depression, short-term memory loss, severe headaches, sleeping problems and dizziness, according to Christopher A. Seeger, the lead lawyer for the plaintiffs.
"We took it like clockwork," said Horn, a receiver who played 12 years with the Kansas City Chiefs, the New Orleans Saints and the Atlanta Falcons and who says he now experiences bouts of dizziness and blackouts. "They don't meet with you to tell you what will happen five years later. Had I known that there were going to be complications, I wouldn't have taken the shots."
In accusing the league of negligence, fraud, fraudulent concealment, negligent misrepresentation and conspiracy, the former players are seeking an unspecified amount of compensatory and punitive damages, and the reimbursement of their legal costs.
The league disputed the suit's claims.
"The N.F.L. has long made player safety a priority and continues to do so," Greg Aiello, a league spokesman, said in a statement. "Any allegation that the N.F.L. intentionally sought to mislead players has no merit. It stands in contrast to the league's actions to better protect players and advance the science and medical understanding of the management and treatment of concussions."
The suit, which was filed in United States District Court in New Jersey, also alleged that the N.F.L. was late to acknowledge the problems raised by repeated concussions, and its efforts to combat the issue were half-hearted.
In recent years, the league has instituted a number of changes to protect players, including penalizing helmet-to-helmet hits. Commissioner Roger Goodell said he would not rule out other rule changes to minimize the potential for head and neck injuries.
In October, the league said it would broaden its study of the effects of concussions after an earlier study was scrapped because of problems in how the data was collected. The new study will include about 1,400 people, from 45 to 59 years old, and divided into three groups. The first group will be retired N.F.L. players; the second will be people who played college football but no professional football; and the third will be a control group of nonathletes who have some medical commonalities with the first two.