# Australian Researchers Identify New Depression Subtype Linked to Body Clock Disruptions

> A study by Australian researchers, published on October 21, 2026, identified 'circadian depression' in nearly one-quarter of severe depression patients, characterized by disruptions to the body's 24-hour clock.

By PrimaryBrief newsroom · Published 2026-10-24T01:32:11.843578Z
Canonical: https://primarybrief.com/article/australian-researchers-identify-new-depression-subtype-linked-to-body-clock-disruptions-4d37808c

Australian researchers, primarily from the University of Sydney's Brain and Mind Centre, identified a new subtype of depression called 'circadian depression' in approximately 23% of individuals with severe depression [1][2][3][4][6]. This discovery was published on October 21, 2026, in The British Journal of Psychiatry [1][2][3][5][6]. The findings, based on data from over 11,000 Australians, suggest that this distinct form of depression is linked to disruptions in the body's internal 24-hour clock [1][2][3][4][6].

This identification of 'circadian depression' opens new pathways for diagnosis and treatment. Recognizing this subtype could lead to more effective, targeted therapies for those who do not respond to conventional antidepressants, potentially preventing prolonged suffering and adverse side effects [1][2][3][5].

## What the records show
The research analyzed clinical and genetic data from 11,380 Australians diagnosed with severe, recurrent, or persistent depression through the Australian Genetics of Depression Study [1][3][4][7]. Out of this cohort, 2,604 individuals, or 23% of participants, were identified as having the circadian depression subtype [1][3][5][7]. This subtype is characterized by specific features related to disrupted circadian rhythms, requiring individuals to exhibit at least three out of six defined characteristics [1][3][4][7]. These features include experiencing seasonal patterns of illness, a delayed sleep midpoint, sleeping longer when depressed (hypersomnia), being a "night owl" (evening chronotype), waking feeling very tired or exhausted, and experiencing social jetlag [1][3][4]. Hypersomnia, reported by 23.8% of the circadian group, and morning tiredness, reported by 23.3%, were among the most frequent symptoms [1]. While 80% of those with circadian depression were female, the study noted that 75% of the overall participants were also female [1].

Individuals with circadian depression typically experience an earlier onset of the illness, around age 18, compared to an average age of 23 for those with non-circadian depression [1][3][4][6][7]. This subtype is also associated with more severe and complex clinical presentations, including more frequent episodes, increased symptom severity such as mania, psychosis-like symptoms, and higher levels of suicidal thoughts [1][2][3][4][6][7]. Genetic analysis further revealed a higher risk for inflammatory and cardiovascular health problems, as well as major neurodevelopmental disorders like ADHD, among those with circadian depression [1][2][3][5][6]. Dr. Emiliana Tonini, first author of the paper from the University of Sydney's Brain and Mind Centre, stated that this indicates "circadian depression is not just depression with bad sleep, but actually there is an underlying biology that is quite distinct from other forms of depression" [3][5].

## The timeline
The concept of a link between mood disorders and disrupted daily rhythms has been acknowledged for some time, with the idea of a body-clock subtype first conceptualized in 2021 [5]. The current study, strengthening this evidence, was published on October 21, 2026, in The British Journal of Psychiatry [1][2][3][5][6].

## What changed and for whom
A critical finding of the study is that circadian depression is more resistant to conventional first-line antidepressants, such as serotonin and norepinephrine reuptake inhibitors (SSRIs and SNRIs), which can sometimes cause adverse side effects in affected individuals [1][2][5]. In contrast, this subtype appears more responsive to behavioral and medical therapies specifically targeting the body clock's unique brain circuits [1][2][4][5]. These include treatments like melatonin, melatonin-targeted antidepressants, and light therapy [1][2][4][5]. The researchers suggest that recognizing this subtype early could lead to more effective treatments and help avoid early treatment failures and unwanted side effects [1][2][4]. Jacob Crouse, a psychiatry researcher involved in the study, noted that "Because circadian depression is linked to people's internal body clock, treatments targeting the circadian rhythm, such as light therapy and melatonin, may be much more relevant, and clinicians should reach for these much earlier in people with this presentation" [4].

## What the researchers say
Dr. Emiliana Tonini explained that the team defined circadian depression as participants showing at least three of the six identified features [3]. She emphasized the severity of the condition, stating that "Individuals with circadian depression have more severe mental health symptoms," including a younger age of onset, more episodes, and more complex trajectories, including suicidality and psychotic-like symptoms [3]. Tonini also highlighted the genetic findings, noting, "This is important because that indicates that circadian depression is not just depression with bad sleep, but actually there is an underlying biology that is quite distinct from other forms of depression" [3].

## What we could not confirm
While the research presents circadian depression as a promising proposal, it is not yet an established diagnosis [7]. Independent experts outside the study have questioned whether the circadian depression group is biologically distinct [7].

## Evidence cited
1. (October 21 2026) In a new study published in the British Journal of Psychiatry, researchers from the University of Sydney said circadian depression is distinct as a 'biologically informed sub-type of depression'. They said circadian depression is more resistant to usual first-line antidepressants such as serotonin and norepinephrine reuptake inhibitors – which can in fact cause side effects in people with this sub-type – but more responsive to melatonin, melatonin-targeted antidepressants and l (racgp.org.au) — https://racgp.org.au/
2. (October 21 2026) Researchers identify new subtype of depression linked to body clock. Source: Xinhua. Editor: huaxia. 2026-10-21 15:57:45. SYDNEY, Oct. 21 (Xinhua) -- Researchers in Australia have identified a subtype of depression linked to disruptions in the body's internal 24-hour clock that regulates the sleep-wake cycle, potentially paving the way for more targeted behavioral and medical treatments. The study analyzed clinical and genetic data from more than 10,000 Australians with severe, (news.cn) — https://news.cn/
3. Australian researchers identify new subtype of depression linked to body clock disruptions (www.theguardian.com) — https://theguardian.com/society/2026/oct/21/australian-researchers-identify-new-subtype-of-depression-linked-to-body-clock-disruptions
4. (October 20 2026) A new study found a quarter of patients fit into a 'circadian' subtype of depression, arising from a state of perpetual jet lag. Led by psychiatry researchers Jacob Crouse and Ian Hickie, a team from the University of Sydney in Australia has published its findings in the British Journal of Psychiatry. Current clinical guidelines treat depression as one disorder. But Hickie and team believe that while depression may look similar for each patient, many different biological proble (sciencealert.com) — https://sciencealert.com/
5. (October 20 2026) Researchers propose a new subtype of depression linked to body-clock patterns. ... Scientists in Australia have proposed that there's a specific form of depression that heavily involves circadian disruptions. (Image credit: ljubaphoto via ... (livescience.com) — https://livescience.com/
6. (October 21 2026) University of Sydney research identifies circadian depression, a new subtype linked to the body clock that may respond to targeted treatments ... Circadian depression is linked to disruptions in the body's internal 24-hour clock, with experts hoping the discovery will lead to alternative and more targeted behavioural and medical treatments. 21 October 2026. Research by experts at the University of Sydney has identified a new subtype of depression called 'circadian depression'.  (sydney.edu.au) — https://sydney.edu.au/
7. (October 23 2026) For some people with depression, every day feels like waking up with jet lag but without the flight. They sleep longer, wake exhausted, and find themselves most alert when the rest of the world is winding down. Their problem may not simply be how much they sleep or how poorly, but when their internal clock tells them to. In an analysis of 11,380 Australians with a history of depression, researchers identified 2,604 people, or 23 percent, whose sleep habits and symptoms fit a pr (zmescience.com) — https://zmescience.com/