About 1 in 4 people with depression may have a ‘body clock’ type, like being stuck in permanent jet lag: late sleepers, tired mornings, worse in certain seasons. Across 11,380 people, this group got less benefit and more side effects from antidepressants, so light therapy or melatonin may help more.

A popular r/science post reports that a University of Sydney team, drawing on the Australian Genetics of Depression Study with 11,380 participants, identified a circadian depression subtype affecting about 23–25% of them, marked by late sleep, morning fatigue and seasonal worsening. This subgroup got less benefit from antidepressants and had more side effects, suggesting light therapy or melatonin may be better matched to them.