SAN DIEGO – Inside linebacker Stephen Cooper walked into the San Diego Chargers’ locker room on Monday carrying three cases of flavored bottled water.

After serving a four-game, NFL-imposed suspension for testing positive for a banned stimulant, Cooper vowed never to use supplements again and to stick with water to fortify his body.

“Honestly, I’m not touching nothing,” said Cooper, who took responsibility for making a mistake. “Supplements are out the door.”

Noting that a second suspension would be for eight games, he said: “That’s too big on the pockets and that’s too big on my heart. I’m definitely going to stay away from that.”

Cooper, who starred at the University of Maine from 1999-2002, said he took “a lot of supplements” to help with recovery after offseason workouts. His suspension was announced on April 15.

“There’s a lot of stuff that I wasn’t really educated on,” Cooper said. “I really wasn’t paying attention to what I was taking and I got caught up.

“They tell you to watch out for what you take, but at the end of the day it’s always up to you and you’ve got to know what you’re doing.”

Cooper led San Diego with 179 tackles in his first season as a starter in 2007, when the Chargers reached the AFC championship game.

He had to watch on TV as the Chargers lost their first two games this season before reaching .500 with wins over the New York Jets and Oakland Raiders.

With the exception of a trip to Massachusetts to watch his 10-year-old son play in a Pop Warner game, Cooper has been working out in San Diego.

“Just that duration of four games, it made me sick,” Cooper said.

The linebacker said he started to cry when the telecast of the season opener came on, “because I wanted to be out there with my teammates.”

The Chargers lost 26-24 to the Carolina Panthers when Jake Delhomme threw a 14-yard touchdown pass on the last play of the game. The next week in Denver, a referee’s blown call and Jay Cutler’s last-minute TD and conversion passes lifted the Broncos to a 39-38 win.

“The first two were tough – as you can see I’m getting gray hairs now,” Cooper said. “Especially that Carolina game, I was sitting on the couch and the next thing you know I was standing on my couch. Watching that game go down the way it did was kind of tough. As you can see, the defense has responded out and they’re playing team defense.”

The Chargers have until Saturday to add Cooper to the 53-man roster and make a corresponding move.

Cooper said he’ll have to compete to win back his starting job. The Chargers play at Miami on Sunday.

“He’s a starter, and anytime you get a starter back it’s a good thing, so we’re happy that he’s back,” general manager A.J. Smith said.

“It’s going to be huge because he’s one of those emotional leaders on the field and he’s one of our better players on the field also,” outside linebacker Shaun Phillips said. “So anytime you can get a guy of that caliber back, it helps us out immensely. It’s going to be fun to have him back on the field.”

While at Maine, Cooper admitted to possession of steroids after being found with about 1,000 pills in his duffel bag when the driver of an SUV he was riding in was stopped for speeding in 2002.

Cooper, who pleaded guilty to a misdemeanor drug charge, said at the time that he never took the steroids, but had been planning to use them to bulk up in hopes of making the NFL. He joined the Chargers as an undrafted rookie in 2003.