We have a new biggest name in a rash of suspension announcements on the eve of the holiday weekend.
Gates blamed his positive test on "supplements and holistic medicines" he used in an effort to recover from the past season.
"In my 12 years in the NFL, I have taken tremendous pride in upholding the integrity of the NFL shield and all that it entails," Gates said in a statement. "I have taken extreme care of my body with a holistic approach and I have never knowingly ingested a substance that was banned by the NFL."
Gates acknowledged that he should have done his "due diligence" to ensure his recovery stayed within NFL guidelines.
"I understand that I am responsible for what is in my body and I have always believed that ignorance is no excuse when it comes to these issues," he added. "I take full responsibility for my actions."
Gates' loss is a substantial one for a Chargers team that has come to rely on his playmaking abilities over the past decade. Gates had a team-high 12 touchdowns last season, and crossed the 10,000 receiving yard mark in San Diego's season finale. An eight-time Pro Bowler and three-time All-Pro, Gates is one of the most productive and popular players in team history.