How does adhd medication affect those without adhd?

Depends on age: Stimulants affect nearly all prepubertal children the same: decreased physical activity, better attention/focus, overall more subdued, no "high"; also decreased appetite & onset insomnia. In adults without adhd, se are the same, as is improved concentration, but most feel energized with mood elevation. Adults with adhd respond like prepubertal children. When/why change occurs not known.

Like +++ coffee: If you don't have adhd, the stimulant will cause irritability, tremors, headache, stomach ache, muscle cramps, insomnia, agitation, & in higher doses hallucinations or hypertension, arrhythmia, or rapid heart rate. In spite of all those, adhd medications are extremely safe.

Side effects : Taking a stimulant without having adhd can increase the risk of side effects