"I made a mistake and take full responsibility," Liuget said in a statement forwarded by NFL Network's Ian Rapoport. "As part of my training program, I placed my trust in someone who, in hindsight, was not well-versed on the NFL's policy on banned substances."
He added: "I apologize to our fans, my family and the entire Chargers organization. I hate that I won't be able to be there for my teammates to start the season, but I will turn this into a positive. When my number is called, you can count on me being ready to answer that call."
A 2011 first-round pick, Liuget has spent all seven of his professional seasons with the Chargers.
The Illinois product thrived over his first four years with the Bolts and parlayed steady production into a five-year, $51 million extension that included $30 million guaranteed.
Last season, Liuget started all 12 games in which he appeared. He finished the year with 21 total tackles, 1.5 sacks and a forced fumble.
He'll now miss the first four games of the regular season as the Chargers eye their first postseason berth since 2013.
“Even though Corey’s mistake was unintentional, he understands how disappointing this is for everyone in the organization," general manager Tom Telesco said in a statement. "I'm pleased he has accepted responsibility on the matter, and we respect and support the League’s decision. We also support Corey. Few people have a bigger heart and have done more for the community. While nobody feels worse than Corey himself right now, we know he will bounce back from this."