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Depression, anxiety, chronic lack of sleep, and a variety of medical conditions can also diminish the ability to focus.

A physical exam should catch many of the physiological causes, so I encourage OP to explore the possibility of psychological causes.

Depression, anxiety and chronic lack of sleep are usually comorbidity with ADHD though.

So if you have any of those AND you have ADHD then treating ADHD will almost always treat those as well. Since ADHD is the cause for those symptoms.

Depression/anxiety are often used as misdiagnosis before someone is diagnosed properly for ADHD.