You'll never run as fast as Chris Johnson ... but you can take what he takes before working out, 'cause the ex-NFL superstar is launching his own supplement line.
TMZ Sports talked to CJ2K -- who retired from football after the 2017 season -- about getting into the MULTI-BILLION dollar supplement industry ... a biz he's dreamed of being in since he was a teenager.
"When I first got to college, I was 150 pounds and I was a smaller guy," Johnson says.
"It was always something I was trying to, some type of supplement or something I was trying to get so I could gain weight and get bigger like the rest of the guys."
"So, I was like, one day I'm gonna come out with my own supplement."
Yeah, Chris ... the guy who ran a 4.24-second, 40-yard dash at the NFL Combine and went on to become a 3-time Pro Bowler who made 1st team All-Pro, won Offensive Player of the Year in 2009, and rushed for over 2,000 yards in a single season (he's 1 of only 7 guys to accomplish that feat) -- wasn't always a physical specimen.