Two-time Super Bowl champion Jim McMahon is among 300 retired players or spouses suing the NFL for concussion-related dementia and brain disease symptoms they claim were suffered on the job.

McMahon, the ex-Chicago Bears star, has been outspoken on the issue and believes the league went so far as to conceal information related to concussions.

“We knew what was going on with pretty much every other part of the body,” McMahon said on ESPN’s Outside the Lines, per ProFootballTalk.com. “We knew there was going to be a chance for injury. But we didn’t know about the head trauma. and they did, and that’s the whole reason for this lawsuit. … They knew about it and they didn’t tell us. That’s like looking in your face and lying to you. Flat-out lying.

“Short-term memory is not good,” McMahon said. “I won’t remember a hell of a lot about this interview in 10 minutes.”

McMahon is part of at least four concussion-related lawsuits that have been consolidated in Philadelphia. The league has vowed to vigorously defend itself.

In a separate class-action lawsuit filed in February in federal court in new Orleans, several former Saints, including John Fourcade, are among 11 ex-players named as plaintiffs. The lawsuit says each of them has developed mental or physical problems from concussions or concussion-like symptoms.

A 2000 survey of more than 1,000 former NFL players found that more than 60 percent had suffered at least one concussion, while 26 percent had suffered three or more during their careers, according to the February lawsuit.

A new study commissioned by ESPN and funded by the National Institute on Drug Abuse suggests that retired NFL players are suffering a lot of pain: 7% are taking at least one prescription opioid painkiller, according to the study, a rate four times higher than that of the regular population.

Combine the findings with a Dec. 2010 report that showed that concussions are up 21% in the NFL this year, and a Sept. 2010 study finding that retired players are 19 times more likely to have dementia or Alzheimer’s than other men ages 30 to 49, and that’s a lot of bad news for pro football players. (More on Time.com: Study: Boys, Girls Suffer Different Concussion Symptoms)

The current study, conducted by researchers at Washington University, St. Louis, surveyed 644 former players who retired between 1979 and 2006 to track their use of prescription drugs, including Vicodin, codeine and oxycodone. about 52% of the players said they had used painkillers during their football careers, and 71% of those had misused the drugs (i.e., they didn’t take the drugs as prescribed or took drugs prescribed to someone else). in fact, 63% of the athletes who had used prescription painkillers during their playing days said they had gotten pills from coaches, teammates, trainers or from the Internet — not from medical professionals.

About 15% of players who had misused prescription drugs before retirement were still doing so after hanging up their jerseys. Players who misused drugs while playing were three times more likely than players who didn’t to continue misusing them after retirement, the study found. (More on Time.com: Down Syndrome Goes Viral, Thanks to a High School Touchdown)

Although the study didn’t indicate levels of drug dependence, it does suggest that ex-NFL players are in pain. “The rate of current, severe pain is staggering,” said lead investigator, Linda B. Cottler, a professor of epidemiology in Washington University’s psychiatry department, in a statement.

Still, the NFL’s medical adviser for substances of abuse, Dr. Lawrence S. Brown, told ESPN that the study was fundamentally problematic. “It is scientifically flawed to compare the general population with athletes, active or retired,” he said, adding that professional athletes are more vulnerable to injury and to prescription-drug misuse than the general population.

But the fact remains that players are suffering — they said so themselves. Only 13% of the players surveyed said they were currently in excellent health; 88% said they had been at the beginning of their careers. (More on Time.com: Could Painkiller Use in Pregnancy cause Problems in Baby Boys?)

The study is published online by Drug and Alcohol Dependence, and a full evaluation of the data is available on ESPN’s outside the Lines.