Jamison Henley of ESPN.com reported the news.
Dixon, 23, was already suspended four games for violating the performance-enhancing drug policy. The Ravens placed Dixon on injured reserve earlier this month after he suffered a torn meniscus during the preseason. He will miss the entire 2017 season but will forfeit six games' worth of salary ($190,588) during the suspension.
"I want to apologize to the Ravens organization, my coaches, teammates and fans," Dixon said in a statement for his first suspension. "Being an NFL player is a privilege that comes with many responsibilities, including knowing the contents of any and all foods and supplements put in your body.
"I mistakenly took a substance without the proper NFL medical exemption, and while it was unintentional, I accept full responsibility for my actions and their consequences. I am truly sorry for the mistake I made and the distraction it causes. Moving forward, I remain committed to focusing on my offseason training, conditioning and game preparation so I can be an immediate impact player for the Ravens when my suspension is over."
The former Louisiana Tech star finished with 382 yards and two touchdowns during his rookie season. He was expected to split carries with Terrance West before the injury and suspension.