Scientists May Have Found a 7th Type of Depression

Staying up late, sleeping long into the morning, and still waking up exhausted — this is a pattern many people with depression might recognize. But what if these sleep habits were more than symptoms of the illness? Researchers in Australia suggest they could be signs of a distinct form of depression.

The idea that a misfiring body clock might do more harm than cause a bad night’s sleep isn’t new. But a study in the British Journal of Psychiatry proposes that people with this cluster of traits may have circadian depression—a potential subtype in which a disrupted body clock is a core feature.

Scientists have tried to make sense of these differences before. In 2024, researchers identified six patterns of brain activity among people with depression, suggesting that different biological profiles could help explain why treatments work for some people but not others. The Australian team is taking a different approach, looking at sleep and circadian traits rather than brain scans.

Outside experts, and even the authors themselves, caution that more research is needed. Still, the findings raise the possibility that disruptions to the body’s internal clock may help drive depression in some people, rather than result from it. If so, treatments targeting those rhythms, such as bright light therapy and melatonin, could offer another approach to managing the illness.

The body runs on a roughly 24-hour cycle, driven by a master clock in the brain’s hypothalamus that tells the body when to feel sleepy and when to feel alert, relying mostly on light to reset itself each day. Glitches in the body clock, such as insomnia and oversleeping, are so common in people with depression that they are part of its diagnostic criteria.

But researchers propose that people with at least three of six traits—seasonal mood swings, late sleep, being a night owl, oversleeping, waking up very tired, and social jet lag, or a mismatch between weekday and weekend sleep schedules—may belong to a narrower subgroup with what they call “circadian” depression.

Out of a cohort of more than 11,000 people, about a quarter fit this description. However, the traits were self-reported, and the team had no wearable data or melatonin measurements to confirm disruptions in the body clock. Their depression tended to begin earlier and was more severe. They also carried higher genetic risk for ADHD, bipolar disorder, and insulin resistance.

(When you go to bed may matter more than how long you sleep.)

The team’s hunch is that, for these people, a “disrupted or dysregulated” circadian rhythm might be what leads to their depression in the first place, says first author Emiliana Tonini, a researcher studying circadian rhythms at the university’s Brain and Mind Centre.

Depression is “an extremely heterogeneous mixed bag of different presentations and causes,” says co-senior author Jacob Crouse, a researcher at the same center, “that leads to a lot of ineffective treatment.” The idea that circadian misfirings could describe a previously unacknowledged subset of people seems to have resonated. Crouse says many people who found the study told him: “That sounds like me, that sounds like my experience, what I’ve tried hasn’t worked.”

In fact, people in the circadian group were more likely to report that antidepressants were less effective. But Crouse acknowledges that this could be explained by factors separate from their body clock biology. “Maybe they have other characteristics that just create a more difficult to treat depression,” he says. Some participants may have also had bipolar disorder rather than depression, says Colleen McClung, a psychiatrist at the University of Pittsburgh.

But experts say it is too soon to define a new subtype. The traits might catch people with more severe depression, says David Curtis, a psychiatrist at the UCL Genetics Institute in London, which could also explain the findings.

(​Are you a "lark" or an "owl"? Your body clock holds the answer.)

Untangling whether a disrupted clock brings on depression or is a consequence of it is difficult. Some studies have found that people who naturally go to bed late, known as “eveningness,” are more likely to be depressed, McClung says, but the evidence isn’t robust. Depression itself can also scramble sleep and daily rhythms, so the link alone doesn’t show which comes first. Another study found a genetic tendency toward sleeping an hour earlier was linked to about 23 percent lower risk of depression.

Another question is whether ‘fixing’ the body clock can improve mood.  A 2025 review found that shifting sleep rhythms earlier was linked to better mood in people who ran on a later schedule. But Curtis says it could signal something else. “As people recover from their depression, their sleep normalizes,” he says.

Still, evidence suggests treatments targeting the body’s internal clock can help. A 2025 review found that among more than 800 people with nonseasonal depression, more than 40 percent reached remission with bright light therapy versus 25 percent of the control group. The researchers behind the Australian study suggest clinicians should consider such approaches earlier, although these trials did not specifically enroll people who fit the proposed circadian depression profile.

The evidence for melatonin as a therapeutic is less robust. One analysis found no clear benefit for depression.

Psychiatry has long struggled to match symptom profiles to treatments, Curtis says, and he isn’t convinced that adding more subtypes would help. Responding poorly to SSRIs, “doesn’t mean they’ll respond better to a different treatment at all,” he says, even though “everyone would love that.”

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Researchers at the University of Sydney are now hoping to investigate that. They’re testing whether melatonin can improve symptoms in young adults who fit the proposed circadian depression profile. The trial could help determine whether identifying people by their sleep and circadian patterns offers a more effective way to treat depression—or simply another way to describe it.