Heroin became big part of the jazz scene in the 1940s, partly due to the influence of Charlie Parker, the leader of the bebop movement who was also a junkie. Lots of musicians at the time believed they would be able to play like Parker if they took smack, and this snowballed into more and more people taking, and in turn inspiring younger musicians to take.
It claimed the lives of many of bebop's greatest players, the death of Parker led to somewhat of a rejection of it.
Many of the greatest used it, examples being Miles Davis, Sonny Rollins, John Coltrane, Jackie Mclean, Fats Navarro, Gerry Mulligan, Chet Baker, Bud Powell, Art Blakey and Stan Getz. Most of their addictions can be traced to Parker's influence over them.
Keith Richards in his "Life" biography talked about the hours and the need to "keep going" through the creative process.
touring all the time means your body is thrown off. you work late - stay up late - need to stay up late and perform with high energy. but traveling means you have to be up early and on the move (especially in tour busses). so uppers and downers become part of the scene just to do the job.
writing, constructing, editing, mixing and mastering the music (given the small amounts of time one may have between shows, tours, albums) = mad dash to get it all done.
Richards talks about using an upper just to get up in the morning, then another drug to ease off, drugs to keep going at a high pace to create albums. He writes that it was just work and trying to get everything done in a short space of time. (Brian Jones, on the other hand, was a junkie - just using drugs to get wasted and couldn't "handle them." Its richard's book so he can say what he wants but his definitions of appropriate vs inappropriate uses for coke/heroin/uppers and downers is interesting).