The Dallas Cowboys aren't only one of the wealthiest sports franchises in the world but also one of the most popular teams in the National Football League.Winners of five Super Bowls and with some of the greatest players in football history going through their ranks, the Cowboys were one of the most dominant teams in the league a couple of decades ago.Nonetheless, it hasn't all been good for America's Team, as some of their standouts have been mixed with off-field controversies. Here, we'll talk about the four best Cowboys players who struggled with drugs and substance abuse.Michael IrvinMichael Irving is known for being the greatest wideout in Cowboys history and for his hilarious, loud rants on television.However, long before that, he was also a bit of a troublemaker.Back in 1996, the superstar was suspended for five games for cocaine possession, also having to pay $500,000 of the $1,200,000 he was due to make that season.As Sportscastingreported, Irvin even had a "White House" full of sex and drugs to appease him and some of his Cowboys teammates.Thomas 'Hollywood' HendersonKnown as one of the most physical specimens in the league during the late 70s', Thomas 'Hollywood' Henderson was a feared and respected linebacker.But Henderson was also a bit of a party animal with severe drug addiction.In fact, he struggled so badly that he even snuck in liquid cocaine to the locker room during Super Bowl XIII, per Michael Weinreb of ESPN:“On the day of the Super Bowl, he emptied a bottle of nasal spray, filled it with a vicious mixture of cocaine and water, and slipped it into the pocket of his uniform pants. Just in case, he thought. He indulged before the game, then again in the third quarter,” reported Weinreb.Randy GregoryRandy Gregory had every single trait to become a superstar. Sadly, anxiety, depression, and substance abuse prevented him from reaching his ceiling.Gregory has been suspended multiple times for weed and has been in-and-out of rehab to try and fight his demons:“Weed wasn’t the problem,” Gregory told Dan Pompei of The Athletic.“It was the solution to my problems, which was another problem in itself.”He's still a part of the team so, hopefully, he'll find the help he needs to stay clean.Leon LettLeon Lett was a bit of a dominant force during his prime. But he wasn't exactly a well-behaved star back in the day.As a matter of fact, Lett wasn't suspended once or twice during his career but a whopping five times.Lett constantly tested positive for weed and cocaine and was even forced to sit out for a whole season for his offenses.Fortunately, the talented DT was able to put his woes behind him and he's been an assistant defensive line coach for the Cowboys since 2011.