The drug use is another thing - Sherlock used cocaine and morphine. House used Vicodin. Morphine and Vicodin are both opioids.
If they had him abuse cocaine, it would be too unrealistic. If they had him abuse Adderall, it might not be obvious to audiences that he has a substance abuse problem - people could write it off as him using it to focus. A prescription opioid is something audiences understood were abused at the time, and maintains the Sherlock connections the writers were going for.
Plus it gives plenty of plot hooks to explore the effects and consequences of addiction to someone we believe to be very successful (success is happiness, right?) in season 1