Why do ADHD and depression often occur together?

Roughly 20-30% of people with ADHD have comorbid depression, and the relationship can take several forms:

Depression secondary to ADHD: years of struggles, perceived failures, low self-esteem, and the sense of not being able to do what others can creates fertile ground for depression. When ADHD is treated adequately, part of the depression often improves as well.

Rejection sensitive dysphoria (RSD): a phenomenon specific to ADHD, an intense, rapid emotional response to perceived rejection or criticism, which can resemble brief, intense depressive episodes.

Shared genetic factors: ADHD and depression have overlapping genetics; some people carry a biological predisposition to both independently.

A tricky differential diagnosis: the two conditions share overlapping symptoms (difficulty concentrating, sleep, motivation, energy). Depression can mask ADHD and vice versa. Getting the order of diagnosis and treatment right matters.

Treatment: treatment needs to address both conditions. Antidepressants that also have evidence for ADHD (like bupropion) can be useful. ADHD stimulant medication can indirectly improve depression by improving functioning. CBT addressing both conditions together is possible with an experienced therapist.