The DSM defines substance use disorder as (roughly) a problematic pattern of substance use that produces clinically significant impairment or distress, demonstrated by at least two of eleven diagnostic criteria within a twelve month period.

It’s not a question of how well represented it is, but the effects it has on the person’s life. Drinking coffee or alcohol or taking prescription medication every day doesn’t qualify as a disorder as long as there’s no negative impact.

Note also that GP said “at one point in their lives”, not that a third or half the world has a substance problem at any given time. A five cup a day coffee addict who quit and had headaches that negatively impacted their work life could qualify, so it’s not all hard drug use either (mostly binge drinking iirc).

Thanks for the clarification.