This means Lewis, who has played exclusively special teams for Detroit this season, will be out for the rest of the regular season. He would be eligible to return to the team if the Lions make the playoffs.
"I apologize to my coaches, teammates, the Lions organization and our fans for my actions," Lewis said in a statement. "I have let my team down and there's nothing worse than that.
"I will not make the same mistake again. I look forward to returning to the team after I serve my suspension."
Lewis, who stands to lose almost $112,000 because of the suspension, has made six special teams tackles this season. He was a seventh round pick by Detroit last season. Lewis did practice with the Lions on Tuesday.
The Detroit Free Press is reporting Lewis was suspended for use of Adderall, which helps treat Attention Deficit Hyperactivity Disorder (ADHD).
"All NFL players know they are responsible for their actions," Lions general manager Martin Mayhew said in a statement. "And they also know there are consequences when their actions are not consistent with league policy.
"While we are disappointed that Travis violated league policy and will miss the next four games, we expect that Travis will learn from this experience and not repeat it."
To take Lewis' roster spot, the Lions signed linebacker Julian Stanford.