In a place where drug use is legal, how would you define 'substance abuse'?

The use of an addictive substance in excess and consuming it to dangerous levels.

Substance abuse is someone who depends on drugs and are heavily addicted

I would define substance abuse is when they can not quit this substance because they are simply addicted or when it causes harm to that persons family,love life, social life, work life and harms their ability of having a job.That is when I believe that there is a substance abuse problem.