How do clinicians separate ADHD fatigue from depression fatigue?

Clinicians separate ADHD-related fatigue from depression-related fatigue by looking closely at how the fatigue presents, when it occurs, and what it’s associated with. In ADHD, fatigue often comes from mental effort and executive overload — struggling to focus, organize, or complete tasks can be exhausting even when you’ve slept well. It’s typically worse during cognitively demanding activities, may fluctuate throughout the day, and often coexists with restlessness, distractibility, or “brain fog,” rather than persistent sadness. Depression-related fatigue, on the other hand, is usually persistent and pervasive, present across activities, and often accompanied by low mood, hopelessness, anhedonia, or sleep changes. Even tasks that don’t require much focus can feel exhausting, and motivation is broadly diminished. Depression fatigue may not improve with breaks or movement, whereas ADHD fatigue sometimes improves with short activity breaks, environmental adjustments, or medication. Clinicians also consider patterns over time, use validated screening tools, and review other symptoms like irritability, sleep, appetite, and functional impairment. Sometimes, both ADHD and depression coexist, making careful history-taking, symptom tracking, and, if needed, trial of targeted treatments critical to teasing them apart.