This substack a summary written by the author of a recently published paper reviewing studies on sleep and ADHD, ADHD as a circadian rhythm disorder: evidence and implications for chronotherapy.

Between 73-78% of people with ADHD have delayed sleep/wake cycles

Cortisol rhythms tend to be both blunted and delayed in ADHD

They review research using morning bright light therapy and melatonin supplements to correct the delayed circadian rhythms. They conclude ADHD symptoms reduce and mood improves significantly when sleep patterns are addressed.

This also reminds me of this Scott Alexander post about AI Psychosis because it discusses bipolar disorder's relationship with sleep. It's not that lack of sleep causes bipolar disorder but for folks prone to bipolar disorder, they don't get sleepy when sleep deprived. Perhaps something similar is going on with ADHD where a sleep phase offset triggers then cascades into exposing otherwise latent symptoms.

The review also calls out how this bidirectional relationship showing up in ADHD research:

Converging evidence indicates that circadian rhythm disruption represents a highly prevalent and clinically important phenotype that interacts with ADHD symptoms in complex, bidirectional ways in a substantial proportion (though not all) of individuals.