Per Jim Wyatt of Titans Online, Lewan was notified of the league's decision Friday and he will sit out the first four games of the regular season.
Lewan addressed the suspension when it was first announced in July, via Wyatt:
"It's going to kill me. It's going to be a horrible situation to sit there on Sundays and have to watch on a TV. To come to a facility that I've been coming to for five, knowing that I am not allowed to come in. It's going to break my heart. It breaks my heart now just talking about it.
"I never meant any ill intention by this, and I am taking full responsibility for the suspension. … I am not running from anything. But it is going to absolutely kill me to know that I won't be out there to help the boys out. If there is a loss, you're always going to wonder: 'Is there something I could have done?' That's a heartbreaking thing."
Lewan said last month he received a notification from the NFL about a drug test that came back positive for ostarine, but said he never knowingly took the illegal substance:
Even though Lewan appealed the suspension, he acknowledged getting the decision reversed would be a long shot.
"It's unfortunate," he told reporters on July 25. "I wanted to make sure I was the one that broke the news. I wanted this to be as little of a distraction as possible. I didn't take anything knowingly and wouldn't cheat the game. I want people to know that I am not a cheater. That's what is most important to me."
The decision means Lewan won't be eligible to play until Tennessee's Week 5 matchup against the Buffalo Bills.
A first-round draft pick in 2014, Lewan has played in 73 games over five seasons. The 28-year-old has made three consecutive Pro Bowl appearances.