What causes depression? The real reasons behind the disease

If you are having thoughts of suicide or self-harm, call or text the 988 Suicide and Crisis Lifeline, or chat at 988lifeline.org. In an emergency, call 911.

A lot of people ask about what causes depression and are hoping for a clean answer, but honestly, there usually isn’t one. That doesn’t mean what you’re going through is any less real or any less treatable. A QuickMD doctor can help you make sense of your situation, whatever it turns out to be.

What causes depression?

Depression rarely has just one cause. That means nothing you did, or didn’t do, caused it by itself.

Depression, also called major depressive disorder, usually comes from several things working together, not just one. As the National Institute of Mental Health puts it, “research suggests that genetic, biological, environmental, and psychological factors play a role in depression.”

Two people can get depression for completely different reasons. And one person can have several of these factors pile up at the same time. Depression can affect anyone. It doesn’t matter how old you are, what you’ve been through, or how good life looks from the outside.

The main factors that contribute to depression

You might already recognize some of these. Here’s what tends to play a role.

Factor	What it means
Genetics and family history	A close family member with depression can raise your own risk. A good number of genes are thought to play a small part; there’s no single “depression gene.”
Brain biology and chemistry	Differences in how brain circuits and chemical messengers communicate.
Hormones and life stages	Pregnancy, postpartum, the menstrual cycle, perimenopause, and thyroid problems can all trigger a depressive episode.
Chronic stress and life events	Loss, trauma, financial strain, relationship strain, or a major life change.
Physical health	Chronic illness, chronic pain, and some medications.
Substance use	Alcohol and other substances can both contribute to depression and make it harder to recover from.

These factors usually don’t work alone. Most people with depression have more than one happening at the same time. Having one or two of these in your life doesn’t mean depression will definitely happen. It just means the door is a little more open than it is for someone else. 

Maybe what you’re feeling is more worry than low mood. If so, our article on anxiety vs. depression explains how the two are different.

Is depression caused by a chemical imbalance?

If you’ve heard that depression comes down to “low serotonin” or one chemical running low, you’re not alone. A lot of people have heard this, and it’s easy to see why. But the real story is more complicated.

A major review of research on serotonin theory looked for a direct link between low serotonin and depression and didn’t find strong evidence that one causes the other, though the finding is still debated among scientists.

Here’s what we know:

• The idea of “low serotonin” by itself is too simple, not the whole story.
• This doesn’t mean depression isn’t real or isn’t biological. Brain chemistry is still involved. Scientists just haven’t found one simple explanation.
• It also doesn’t mean antidepressants don’t work. Many people feel much better on them. They seem to work by changing how brain circuits function over time, in ways scientists are still studying. It’s not as simple as adding back one chemical.

Some people worry that if depression is “just” a chemical problem, they should be able to fix it on their own. Others worry that if it’s not purely chemical, it might be their fault. Neither is true, and treatment doesn’t hinge on which explanation turns out to be right. Our article on how depression is treated covers what actually helps and why.

Can life events and stress cause depression?

Yes, and if you can point to something that seems to have set this off, that doesn’t make what you’re feeling any less real, or any more “just situational,” than someone else’s. 

A breakup, a death in the family, losing a job, money trouble, or any big change can be enough to set off a depressive episode, especially if you were already more vulnerable to begin with. It’s not always one big moment, either. Grinding, ongoing stress can wear a person down over months or years just as much as a single hard event can. 

Some people never land on a clear trigger, and that’s normal, too. When that happens, biology and genetics are likely doing more of the work.

Medical conditions and medications that can cause depression

What feels like depression can sometimes come from a physical health problem, which is why a doctor may check things like your thyroid before or alongside treating depression itself. The reverse happens too: living with depression can make a physical illness harder to manage.

The National Institute of Mental Health notes that depression often shows up alongside other health conditions, like diabetes, heart disease, cancer, or chronic pain, and each one can make the other harder to live with. Sometimes a medication taken for a physical illness carries side effects that contribute to depression symptoms, too, which is worth mentioning to whoever prescribed it.

Depression is not a character flaw

Depression doesn’t happen because someone is weak or isn’t trying hard enough. 

It’s a real medical condition, and “just snapping out of it” isn’t something willpower can do any more than willpower could set a broken bone. Depression is common; it’s not your fault, and treatment can genuinely help, even on days when that feels hard to believe.

When to talk to a doctor about depression

You don’t need a fully worked-out theory of why you feel this way before it’s worth mentioning to a doctor. If low mood or a loss of interest has stuck around for most of the day, nearly every day, for two weeks or more, or it’s getting in the way of your work, relationships, or daily life, that’s worth bringing up.

You don’t need to know the exact cause to get help, though understanding it can still be useful. Treatment works for most people, no matter what set it off, and that includes therapy, medication, or a combination of the two. If what you’ve noticed matches the signs covered in our article on depression symptoms, it’s worth a conversation even if you’re not sure it “counts.”

If you are having thoughts of suicide or self-harm, get help now. Call or text 988 to reach the Suicide and Crisis Lifeline, or chat at 988lifeline.org. In an emergency, call 911.