Bette Davis said that in the 1930s, the use of marijuana was rampant in Hollywood. 
She said that producers, and therefore directors, had no patience for pot smokers because use of the drug interfered with actors remembering their lines, resulting in multiple takes, which were time consuming and expensive. If an actor or actress was known to use the intoxicant, he or she would not be given parts and his or her contract would be cancelled.
Davis said that it was well known among contract players and at least some directors that Ronald Reagan was a regular marijuana user. Remarkably, however, he never forgot his lines. Consequently, his career was never interrupted.