My personal experience leads me to believe that there is no way Elon Musk could have been dosing stimulants for the last 10-20 years and look as good and as relatively calm as he does. You build a tolerance very quickly, and any edge that you thought the stimulants were giving you will fade away fast. Then, if you increase the dose, your life will spiral off the rails as you become more manic, impulsive and irrational (eg: gambling, sex, spending sprees, irritability, violence, paranoia). Just Google John McAfee if you want to see what this can look like.
IMO Elon Musk just has lucky genetics and doesn't need much sleep, always has high energy. There are people who are fortunate to be born like that.