In fairness to Judy, the studio executives got her hooked on uppers and downers when she was still a child actress.
They needed her to deal with the long hours on the set and not much recovery time for rest.
It was straight up child abuse but was overlooked and covered up...like everything else in Hollywood.
Not disagreeing with you because I don't know for sure, but I once read she was put on benzedrine to help her control her weight and that was how she got hooked.
About Rooney, it appears when he was 19 he had a torrid affair with 39 year old Norma Shearer, at the time a major actress at MGM. It didn't last long. (1940s)