How serious is prescription drug abuse? and what do they define as abuse?

Abuse: Is misuse of medication, such as taking more than prescribed, or continued use when not in need.

Formal answer: Use = use abuse = use when you have on good authority not to use. (tobacco use is always abuse). Alcohol use in under 21 yo is always abuse. Illicit drug use is always abuse. Addiction = drug seeking, dose increasing, losing interest in healthy activities. Dependence = having physical symptoms of illness if drug is not used.