# New depression subtype linked to body clock disruptions

> Australian researchers identify circadian depression, affecting a quarter of those studied, which responds poorly to standard antidepressants.
- Title: New depression subtype linked to body clock disruptions
- Summary: Australian researchers identify circadian depression, affecting a quarter of those studied, which responds poorly to standard antidepressants. Australian…
- Keywords: circadian depression, depression subtype, body clock disruptions, antidepressants, mental health, australian research, university of sydney, light therapy, melatonin, sleep disorders, news, world
- Source: the Guardian — https://theguardian.com/society/2026/oct/21/australian-researchers-identify-new-subtype-of-depression-linked-to-body-clock-disruptions
- Published: 2026-10-20T23:00:48+00:00
- Read time: 1 min
- Topics: circadian depression, depression subtype, body clock disruptions, antidepressants, mental health, australian research, university of sydney, light therapy, melatonin, sleep disorders, news, world
## New depression subtype identified
Australian researchers have identified circadian depression, a new subtype linked to disruptions in the body's internal clock, published in the British Journal of Psychiatry.
## Nearly a quarter of participants affected
The study involved clinical and genetic data from eleven thousand three hundred eighty Australians with mostly severe and recurrent depression. Circadian depression affected nearly a quarter, or twenty three percent, of participants.
## Six features define the condition
Dr Emiliana Tonini of the University of Sydney's Brain and Mind Centre defined circadian depression as showing at least three of six features: seasonal illness pattern, delayed sleep timing, sleeping longer when depressed, being a…
## More severe symptoms and earlier onset
Individuals with circadian depression have more severe mental health symptoms, younger age of onset, more episodes, more complex trajectories, more suicidality, and more hypomanic and psychotic-like symptoms than those with non-circadian depression.

> Individuals with circadian depression have more severe mental health symptoms
## Distinct underlying biology identified
Those with circadian depression had higher genetic risk for ADHD and mood disorders, plus metabolic and inflammatory markers. Dr Tonini said this shows circadian depression has distinct underlying biology, not simply depression with bad sleep.
## Poor response to standard treatments
SSRIs and SNRIs, typical first-line antidepressant drugs, were less effective and had more side effects for people with circadian depression.

> What is critical about being in this circadian type is its poor response to the standard therapies
## Chronobiological treatments recommended
For circadian depression, Prof Hickie recommended chronobiological treatments focused on the sleep-wake cycle, particularly morning light exposure, daylight activity, regularity of sleep-wake cycles, and regularity of food schedules.
## Key takeaway

Australian researchers identified circadian depression, a new depression subtype affecting 23 percent of 11,380 participants, which responds poorly to standard antidepressants and may benefit from light therapy and melatonin.