What Causes Depression

*Content advice: this article briefly mentions suicidal thoughts and self harm. If you are in immediate danger, call 000. Lifeline, the national crisis lifeline, is on 13 11 14 with chat at lifeline.org.au. Beyond Blue is on 1300 22 4636.*

Most pages answering this question say depression is caused by a chemical imbalance in the brain. That explanation has been out of date for years, and the bodies that once promoted it have quietly stopped.

At the Energetics Institute, Richard and Helena Boyd have practised in Perth since 2005. This page sets out what contributes to depression, how much weight each factor carries, and where the science is unsettled.

On scope: we are psychotherapists, so we do not diagnose clinical depression. That is done by a GP, psychiatrist, psychologist or other qualified mental health professional.

The Short Answer

Nothing causes depression on its own. That is the finding, not a dodge.

Depression is the most common mental health condition we see, and the current standard reference, a 2023 review in Nature Reviews Disease Primers, concludes it results from genetic and environmental influences, psychological factors and biology.

One analysis it cites identified 37 risk factors, each accounting for very little alone. So the useful question is not what causes depression, but what stacked up for this person, which is also the more practical question because several contributing factors can be changed.

Is Depression A Chemical Imbalance?

No, and this was never quite what researchers believed.

Beyond Blue states it plainly: depression is not simply the result of a chemical imbalance, like having too much or not enough of a particular brain chemical. The Royal College of Psychiatrists called the idea that antidepressants correct an imbalance an oversimplification in 2019, and neither the National Institute of Mental Health nor the Centers for Disease Control and Prevention describes mental disorders that way now.

The phrase came largely from pharmaceutical marketing in the 1990s and stuck because it is easy to say. Brain chemicals matter, and the messengers passing signals between nerve cells help regulate mood. A single deficiency you can top up is what is not supported.

What The Serotonin Review Found

In 2022 a research team published an umbrella review in Molecular Psychiatry examining every major line of serotonin research.

Across serotonin metabolites, receptor binding, transporter studies, tryptophan depletion and the serotonin transporter gene, they found no consistent evidence linking serotonin to depression, and no support for the idea that it is caused by lowered serotonin activity.

The review was strongly contested. More than thirty researchers replied in the same journal, arguing it misread parts of the imaging evidence and slid from a defensible claim, that there is no simple deficiency, to a much stronger one, that serotonin is not involved at all. The debate is live.

Why That Does Not Mean Antidepressants Do Not Work

This is the part that gets lost, and it matters more than the rest of the section.

Whether low serotonin causes depression and whether selective serotonin reuptake inhibitors work are two different questions, answered by different evidence. As one UCL psychiatrist put it, most of us know paracetamol helps a headache, and nobody thinks headaches are caused by a paracetamol shortage.

Efficacy was settled by trials. A 2018 network meta-analysis pooled 522 randomised trials covering more than 116,000 people and found all 21 antidepressants beat placebo, with small to moderate effects. The Royal College of Psychiatrists was explicit that nobody should stop antidepressants because of the serotonin review. Do not change medication because of anything here. Talk to your prescriber.

What We Do Know About The Biology

Several biological findings are better supported than the serotonin story, with one shared limitation.

The most replicated is dysregulation of the stress hormone system, the HPA axis, which plays a significant role in how the body handles sustained pressure. Inflammation is elevated in a subgroup and tracks particular symptoms of depression such as fatigue, appetite change and sleep disturbance rather than all. Brain network changes are documented at group level.

The limitation is the same in each case. These are population averages, not tests for an individual, and no blood test or brain scan can diagnose depression.

Genetics And Family History

Depression runs in families, and the numbers are more moderate than most people assume.

Twin studies put the heritability of major depressive disorder at around 37 per cent, meaning roughly 63 per cent of the variation comes from environment specific to the individual. Shared family environment contributes almost nothing, and having blood relatives with depression raises your risk without setting it.

The architecture is diffuse. The largest study to date, covering more than 688,000 people with depression, found 697 associated variants, each with a tiny effect. There is no depression gene, genetic testing has no predictive role, and the older story about a serotonin transporter variant interacting with life stress failed to replicate.

Early Life And Trauma

Childhood adversity is among the strongest environmental contributing factors we have good evidence for.

A meta-analysis of prospective studies, which avoid the recall problems weakening most trauma research, found childhood maltreatment roughly doubled the odds of adult depression. Physical or sexual abuse, neglect and emotional abuse all feature, with sexual abuse carrying the highest odds.

It also shapes the course. Maltreatment predicts onset around four years earlier, a more chronic course, and poorer response to mental health treatment. That is not a life sentence, but it is a reason to treat early trauma as clinical material.

Stressful Life Events

Difficult life events genuinely trigger depression, and one study design proved it rather than just observing it.

Using twin pairs to separate cause from shared vulnerability, researchers found independent stressful events, ones the person did not bring about, nearly tripled the odds of an episode the following month. They added that not all of the association is causal, since some people are prone both to encounter stress and to become depressed.

Bereavement, relationship breakdown, job loss and serious illness are the traumatic events we see most, and onset usually follows within weeks.

Personality And Thinking Style

Certain personality traits raise risk, and the effect is large enough to matter.

The clearest is a tendency to feel negative emotion strongly and react hard to stress. Alongside it sit low self esteem, a self critical internal voice, perfectionism and rumination, the habit of turning a problem over without resolving it.

Two caveats. Some of the apparent effect comes from overlap in how these traits and depression symptoms are measured, and personality is a risk marker rather than a character flaw.

Physical Illness, Medications And Substances

Sometimes the cause is medical, which is why a first presentation warrants a check by a healthcare provider.

Overt thyroid problems are the clearest example of a physical illness producing a depressive syndrome, and other medical conditions contribute. Depressive disorders travel with chronic health conditions including chronic pain, diabetes and heart disease, running around 39 per cent in chronic pain populations. Untreated physical health problems make everything harder to shift, and corticosteroids and interferon are the best documented medications.

Drug and alcohol use runs both ways. Alcohol worsens depression and depression drives drinking, and smoking roughly doubles risk in genetic studies testing direction.

Hormones And Reproductive Life

Women experience depression more often than men, and reproductive events account for part of the difference.

In Australian data, 5.7 per cent of women had a depressive episode in a year against 4.1 per cent of men. Three periods carry elevated risk: the premenstrual phase, pregnancy and the year after birth, and the menopausal transition. Perinatal depression is the most studied, affecting around one in ten women during pregnancy and one in seven in the first postnatal year. Prior mental illness is the strongest predictor of postnatal depression.

Premenstrual dysphoric disorder affects an estimated 1.6 per cent of menstruating women when confirmed with symptom diaries, against a manual range of 1.8 to 5.8 per cent.

Social And Economic Circumstances

Circumstances shape both who becomes depressed and who stays depressed, and the second effect is larger.

A meta-analysis found low socioeconomic status raised the odds of developing depression modestly but roughly doubled the odds of it persisting. Loneliness is a strong prospective risk factor, with people who are often lonely more than twice as likely to develop depression.

Unemployment runs both ways, and its independent effect shrinks once prior mental health is accounted for. Material circumstances get far less attention than brain chemistry despite carrying more weight.

How It All Fits Together

The model researchers actually use is vulnerability plus stress, and it is less tidy than a chemical explanation.

You carry a level of genetic vulnerability, shaped further by early life. Circumstances, relationships, physical health and events load on top. At some point the load exceeds what your system absorbs. A sad mood stops lifting, feeling sad gives way to a flatter depressed mood, interest goes, and day to day responsibilities become heavy enough that other symptoms consolidate into an episode lasting at least two weeks.

That explains something people find confusing. Two people can face the same event and only one becomes depressed, and the same person can go under at forty over something they weathered at twenty.

Can Depression Be Prevented?

Partly, and the honest answer has a time limit on it.

Psychological prevention programmes for people with mild symptoms cut new episodes by roughly a third to a half over twelve months. Beyond that the benefit is undemonstrated. Among lifestyle changes, physical activity has the strongest causal evidence, along with not smoking, treating insomnia and keeping social connection.

What lacks the evidence its promotion suggests: vitamin D, anti-inflammatory drugs and most of what is sold for mood. Nothing will reliably prevent depression, and nobody develops it through failing to do these things.

What This Means For Treatment

Understanding the causes changes what an effective treatment looks like.

Because depression is multifactorial, several routes in work. Talk therapy is one, and the psychological treatments with the best evidence are cognitive behaviour therapy, behavioural activation and interpersonal therapy. Medication is another, and combining them helps in more severe depression. Repetitive transcranial magnetic stimulation is an option where medication has not worked.

Be realistic about the arithmetic. Around a third reach full remission on a first antidepressant and roughly half see substantial improvement, so most need more than one attempt. Claims that eight or nine in ten improve immediately are not supported by any trial.

How We Work With This

Our approach is Integrative Body Mind Psychotherapy, which starts where most of the causal weight sits.

Genetics and biology are real and mostly not modifiable. Early life, unresolved trauma, relationships, how you treat yourself and how your body holds chronic stress are modifiable, and that is our territory.

Some people start with a GP, some with someone in their faith community, and either is a reasonable first step for mental health conditions. We work alongside your mental health provider rather than instead of them.

What This Looks Like In Practice

These are composite examples drawn from our clinical work, with identifying details changed.

A man in his fifties wanted to know which parent he got it from, since both had been depressed. What emerged mattered more than heritability: a childhood where nobody was available, and a conclusion formed by six that needs were an imposition.

A woman in her thirties became depressed after a promotion, which made no sense to her. The job had removed the only part of her week that was not performance, and that loss stayed invisible until we mapped it.

A woman in her forties had been told she had a chemical imbalance and stopped looking further. She had chronic pain, a marriage she had gone quiet in, and no sleep. All three were treatable.

Frequently Asked Questions

The questions people ask us most often about this, and our honest answers.

Is Depression Genetic Or Environmental?

Both, and neither alone. Twin studies attribute around 37 per cent to genetics, leaving most of the variation to individual environment and chance. A family history raises risk without determining it, and plenty of people with no family history develop depression.

Can Depression Happen With No Reason At All?

It can arrive without an obvious trigger, which is common and does not mean there is no explanation. Vulnerability accumulated over years does not announce itself, and slow contributors like isolation, chronic pain or long-running stress rarely feel like events.

Does Depression Cause Chemical Changes Or Do Chemical Changes Cause Depression?

Probably both, and the arrow is hard to pin down. Depression is associated with measurable changes in stress hormones and inflammation, and those changes in turn affect mood, sleep and energy. Sorting cause from consequence is one of the harder problems in the field.

Is Bipolar Disorder Caused By The Same Things?

Not quite. Bipolar disorder is a mood disorder involving mood swings between depression and mania, and it is more heritable than depression and less driven by circumstance. It sits separately in the Diagnostic and Statistical Manual published by the American Psychiatric Association and is treated differently.

Where To Go From Here

The key facts depression research has settled on are less satisfying than a single cause and more useful. Genetics load the odds without deciding them. Early adversity, life events, circumstances, physical health and habitual thinking all contribute. Biology is involved, but not as an imbalance you can correct.

That matters practically. If depression were purely a chemistry problem there would be one thing to fix. Because it is not, there are several places to intervene, and the ones with most leverage are usually the ones you can act on yourself.

If you want to work out what has been stacking up for you, that is what the first few sessions are for. We see people individually and as couples at our Inglewood rooms and online across Western Australia, no referral needed.

Call us on 1300 956 227, book a session, or read more about our depression counselling and the signs of depression.