People living with untreated ADHD have a tendency to self-medicate. When ADHDers self-medicate, their drug of choice can range from mostly benign (like coffee) to unhealthy but legal (like cigarettes) to potentially more problematic (like alcohol). And in some cases, logically enough, ADHDers end up self-medicating with stimulants. It’s not hard to see the rationale here: for the ADHD brain, illicit stimulants can perform some of the same functions as legal ADHD medications like amphetamine and methylphenidate.