JaMarcus Russell is opening up about his codeine use in college and the NFL ... saying he would drink lean to cope with injuries instead of taking painkillers.
Of course, the troubled history of Russell is well-known ... from his short venture with the Oakland Raiders (2007-2009) to being arrested in 2010 for possession of codeine syrup.
The 36-year-old says he first drank lean when he was just 14 -- when he accidentally grabbed it (thinking it was soda) from a cooler while hanging out with friends at a park in Mobile, Alabama.