Sometimes people worry that something bad in their past would prevent them from being able to file a lawsuit. First of all, there are no restrictions to filing a lawsuit other than filing it too late - the dreaded statute of limitations. The real question is whether this bad thing would cause them to perhaps lose their case. While I won't make a blanket statement that would apply to all people for all possible things, I can tell you that most times the bad thing makes no difference - provided of course, you told your lawyer about it. Lawyers need to know about things to deal with them.
I had a client who had used cocaine for a number of years. He found religion and gave it up. His prior cocaine use was part of his medical history, contained in his medical records. In the course of his medical malpractice case, depositions were taken. The defense attorney asked my client questions about this drug history. His treating doctors were also questioned about this. The medical experts, both the one I hired and the one the defense hired, talked about the cocaine and all the bad things that cocaine can do. I'm sure that the defense attorney thought that he would use this past history to discredit my client, to make him less believable. Maybe he thought a jury wouldn't want to find a doctor guilty of malpractice, awarding a prior cocaine user a large verdict.
In this particular case, the jury was never going to know about the prior cocaine habit. Why? Because it was irrelevant and highly prejudicial. In this case, there was no evidence or testimony provided by any of the doctors that the cocaine use of years before had caused any medical condition to my client that was any way related to the medical condition we were suing for. That made it, therefore, none of the jury's business.