How does ADHD affect cognitive effort and mental fatigue?

Everyday tasks often require more conscious effort for people with ADHD. Planning, remembering, focusing, switching tasks, and regulating emotions all draw on executive functioning. When those systems are less efficient, daily life becomes mentally taxing. This leads to cognitive fatigue even on days that don’t look busy from the outside. Rest alone doesn’t always help because the fatigue comes from constant mental regulation. Clinicians often hear people say they’re tired of thinking. That experience is very consistent with ADHD related executive load.