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.