Well...
Oniw17, it wouldn't make sense that Bruce was a cocaine user because he never manifested the physical symptoms of being a cocaine user. For example, Bruce's resting heart rate was on average around twenty something beats per minute (extremely low!) In fact, at UCLA facilities where he got his June 1973 physical it was also very low. A cocaine user would have a higher than normal heart beat.
Bruce worked out hard, but that's very possible without drugs. Look at Olympic gymnasts and marathon runners and such. They don't use drugs, yet they push their bodies to the limits. Bruce was no different... and he was a very serious, dedicated, and disciplined martial artist, which is why he pushed himself so hard.
Bruce actually stopped working out the last few months of his life (as he was told to by physicians). He had become lethargic and a bit ill and had lost a large amount of weight for no apparent reason. He was under enormous pressure and he had definitely overworked himself. He became an insomniac the last year of his life and was experiencing frequent mood changes, depression, and anxiety attacks according to some loved ones. For those reasons, it is VERY possible Bruce used some sort of tranquilizer to relax him (and by very possible, I mean he DID use tranquilizers). I don't believe any were illegal (other than the marijuana, which actually isn't even a tranquilizer), but I do believe he became overdependent on them.