Body-Clock 'Circadian Depression' Subtype Found in a Quarter of Patients

The work is an observational, cross-sectional study, published in 2026 in The British Journal of Psychiatry. It drew on the nationwide Australian Genetics of Depression Study. Of the participants, 2,604 (23%) were classed as having a "circadian" subtype of depression. They were 80% female, with an average age of about 38. Observational means the researchers compared groups of people. They did not test a treatment.

The team defined the subtype by sleep and body-clock traits. A person qualified by meeting at least three of six features: social jetlag, seasonality, a late sleep midpoint, an evening chronotype (being a night owl), morning tiredness and hypersomnia (sleeping too much).

Compared with people without the subtype, this group reported an earlier age at onset. They also reported more severe features: (hypo)manic-like and psychotic-like experiences, suicidality, psychological distress and physical complaints. They reported weight gain during depressive episodes too. The study says all of these differences were statistically significant.

Medication findings were self-reported. The circadian group reported a poorer response to selective serotonin reuptake inhibitors, or SSRIs (odds ratio 0.88, 95% confidence interval 0.82 to 0.94). They also reported a poorer response to serotonin– noradrenaline reuptake inhibitors, or SNRIs (odds ratio 0.89, 0.83 to 0.97). An odds ratio below 1 here means lower odds of a good response. This group also reported more side effects.

The researchers also looked at polygenic risk scores, which add up many small inherited variations into one estimate of a person's genetic tendency toward a trait. The circadian group scored higher for ADHD, major depression, anxiety and bipolar disorder, with odds ratios of 1.09 to 1.11. They also scored higher for body mass index, triglycerides, interleukin-6 (an inflammation marker) and insulin resistance, and for later sleep midpoint and insomnia. These effects are modest, and they are links, not causes.

The design has limits. Data were collected at one point in time, so it cannot show that body-clock disruption causes depression or poor drug response. The authors say the findings support the face validity and potential clinical utility of the subtype as a clinical profile. They add that independent replication is needed, and that its biology and predictive value need further study.

It said the subtype is more responsive to light therapy, melatonin and melatonintargeted antidepressants. The study reports no test of those treatments. The coverage also put the full sample at more than 10,000 people. Co-senior author Dr Jacob Crouse was quoted there saying that treatments targeting the circadian rhythm "may be much more relevant." Professor Ian Hickie said not recognising the subtype in young people often led to early treatment failures and more side effects.

What to watch next

What to watch next is whether other research groups reproduce the subtype, and whether trials show that body-clock-focused treatments work better for it.

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