Jackson tested positive for Adderall, The Baltimore Sun reported.
His suspension begins immediately, according to the league. If Baltimore clinches a playoff spot, Jackson will be eligible to return to the active roster on the day after the team's first playoff game.
Jackson, a rookie fifth-round pick, has only played in three games this season. He has one special-teams tackle.
His suspension opens a roster spot. The vacancy could be filled by linebacker Ray Lewis, who is eligible to return this week from injured reserve. Lewis has been sidelined since Oct. 14 with a torn right triceps.
Information from The Associated Press was used in this report.