The fifth-year pro said in a statement released by the team that he took an Adderall pill without a prescription "around the beginning of training camp." He will not appeal the ban, which begins Sunday against the Kansas City Chiefs.
Talib was the 20th overall pick in the 2008 draft and is one of the team's top defenders with 18 career interceptions. He also will miss games against New Orleans, Minnesota and Oakland, becoming eligible to return to the active roster on Nov. 5, the day after Tampa Bay faces the Raiders.
"I have spoken with Aqib, and he knows that he made a poor decision that let our team down," Bucs first-year coach Greg Schiano said. "Certainly, other players will have the opportunity to step up while he serves this suspension."
It's the second suspension of Talib's career.
The 26-year-old was suspended without pay for the 2010 regular-season opener and also fined one additional game check for violating the NFL's personal-conduct policy. That discipline stemmed from an altercation with a St. Petersburg cab driver during training camp in August 2009.
"I made a mistake by taking an Adderall pill without a prescription. This is especially regrettable because, for the past several months, with Coach Schiano's help, I've worked very hard to improve myself -- professionally and personally -- as a player and a man," Talib said.
"I am truly sorry to my teammates, coaches and Buccaneers fans, and I'm disappointed in myself. I will work diligently every day of this suspension to stay in top football shape and be ready to help this team in the second half of the season. I have chosen to be immediately accountable for the situation I put myself in, which is why I will not exercise my appeal rights and will begin serving the suspension immediately."
The Bucs placed Talib, who has one interception and a team-leading seven passes defensed, on the reserve/suspended list. Defensive end Markus White was promoted from the practice squad to fill the roster opening.
There was no immediate announcement on who'll step into Talib's spot in the starting lineup.