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This is general information about depression, not advice about anyone's own treatment. It does not tell you to start, stop or change a medication. Stopping an antidepressant suddenly can cause real withdrawal effects, so that conversation belongs with a doctor. If you are in danger right now, please contact your local emergency number or a crisis line instead of reading on.
Depression is caused by a chemical imbalance in the brain. Low serotonin, corrected by a pill.
Almost everyone has heard this. It is worth knowing where it came from.
It began as a hypothesis in the 1960s, working backwards from drugs that seemed to help.
If a drug that raises serotonin lifts mood, perhaps low serotonin caused the problem. A reasonable guess.
Aspirin helps a headache. That does not mean headaches are caused by too little aspirin.
The logic is the same shape, and it is the same mistake.
In 2022 a team gathered every major review of the serotonin evidence: levels in body fluids, receptor binding, transporter imaging, gene studies, and depletion experiments.
What did they find across all of it?
It does not mean depression is imaginary. It does not mean the drugs do nothing.
It means the specific story — a serotonin shortage, corrected — is not what the evidence shows.
This review was disputed. Thirty-six researchers published a reply in the same journal saying it was unfair to the field.
What survives the argument: nobody produced the consistent evidence the popular story assumes exists.
Medicine treats plenty of things whose mechanism is unsettled. Migraine. Many autoimmune conditions.
Not knowing why something works is different from not knowing whether it works.
This has been measured very carefully, and the answer is yes, on average, by a modest amount.
In 2018 researchers pooled 522 trials covering about 117,000 people, comparing 21 antidepressants.
All 21 beat placebo. The average effect was small to moderate.
It means the drugs help, and it means they are not a switch.
Some people improve a lot. Some notice little. An average hides both.
Talking therapy has been measured against medication directly, head to head, across many trials.
Which came out ahead?
This is the part most people have never been told. It is not medication or nothing.
Two different treatments work about as well as each other.
Having both does better than having either alone, at least in the short term.
Against medication alone, the combination stayed ahead in major depression for up to two years.
Compared with therapy alone, the advantage of adding medication faded by follow-up.
That is a real finding and it is worth saying rather than hiding.
If the chemical-imbalance account is not what the evidence shows, does it matter what people believe?
It turns out to matter quite a lot.
Researchers gave people feedback saying their low mood came from a chemical imbalance, and measured what happened next.
What happened to how they expected to recover?
Told your problem is a fixed fault in your chemistry, you expect less of yourself and of getting better.
The belief does its own damage, separately from the illness.
The same researchers tried a different message: biology changes.
People told that brains are malleable came out less pessimistic and more able, and the effect lasted.
Brains change with sleep, with exercise, with practice, with therapy, with drugs, with time.
Biological does not mean fixed. That was the error inside the old story.
Nobody knows exactly what causes depression. Several things reliably help. Two of them work about equally well and can be combined.
And none of it is settled by chemistry you cannot change.
Everything here describes averages across thousands of people. None of it can say what will work for one person.
That conversation is with a doctor, and it is a reasonable one to start.