Circadian depression affects 23% of severe cases

A study involving 11,380 Australians found that nearly a quarter of those with severe depression exhibit signs of a disrupted biological clock, known as the circadian subtype. This type of depression may respond less effectively to standard antidepressants.

Study conducted by Australian institutions

The research was carried out by the QIMR Berghofer Medical Research Institute and the University of Queensland. It was published in The British Journal of Psychiatry on October 20, 2026, and included 2,604 individuals, or 23%, who fit the circadian depression profile.

Circadian depression has distinct features

This subtype is marked by an earlier onset of depression and more severe symptoms. Patients in this group also tend to derive less benefit from the most commonly prescribed antidepressants, according to the study's authors.

Six criteria identify circadian subtype

Researchers used six indicators related to the body's internal clock to identify the circadian subtype. These included sensitivity to seasons, delayed sleep patterns, evening temperament, fatigue upon waking, hypersomnia during depressive episodes, and "social jet lag," which refers to the difference in daily schedules between workdays and free days.

Circadian depression patients are younger

Compared to those with other forms of depression, individuals with the circadian subtype are, on average, younger, with a mean age of 38 years.