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Is Depression Caused By a Chemical Imbalance?

Depression is a serious mental illness that can have devastating effects on a person’s life. And it is also one of the most common forms of mental illness, with more than 8% of adults in the U.S. suffering from some form of depression each year. (1) Despite its prevalence, the exact cause of depression is more or less unknown. Though past research pointed towards chemical imbalances in the brain, new scientists are beginning to question that theory. This could completely change the way we treat depression. 

Is Depression Caused By A Chemical Imbalance In The Brain?

For decades, we have been told that the cause of depression is a chemical imbalance of the hormone serotonin in the brain. Serotonin is a neurotransmitter, which means it helps to send messages from one part of the brain to another. It is thought that people with depression have lower levels of serotonin than normal and that this chemical imbalance causes their symptoms.

However, a number of researchers are beginning to question this theory. The most recent evidence suggests that while serotonin is involved in depression, it is not the cause. Instead, it may be one of many brain chemicals that affect how we experience and express emotion. (2)

The Old Theory

The theory behind the idea that serotonin levels, specifically low ones, cause depression came from psychiatrist Max Hamilton in 1960. Hamilton published a paper that suggested serotonin levels were associated with depression, and this became the accepted theory for decades. Researchers soon began looking for ways to increase serotonin levels in the brain to treat depression. (3)

The New Theory

Now, researchers know that serotonin is involved in many other processes in the brain besides depression. For example, it helps regulate sleep and feelings of satiety (fullness). Serotonin levels are also connected to anxiety disorders such as obsessive-compulsive disorder and social phobia. (4)

The new theory is that low serotonin levels may be just one part of the puzzle leading to depression. It’s also possible that other chemicals in the brain are involved in causing depression, such as dopamine and norepinephrine. This theory is supported by the fact that selective serotonin reuptake inhibitors (SSRIs) are not always effective at treating depression. SSRIs work by increasing serotonin levels in the brain, but they don’t work for everyone who takes them.

Not Just One Theory

There are several other theories about what causes depression. One is that the lack of certain neurotransmitters like serotonin and norepinephrine may trigger depression, but there could also be a genetic predisposition to the disorder. A third possibility is that environmental factors such as stressful events in life can lead to depression by triggering biochemical changes in the brain.

There is also the theory that depression is a disease of the brain and body. It’s true that depression can be linked to an imbalance of certain chemicals in the brain, but it’s also true that there are many other factors involved.

The Truth Is: No One Really Knows

Essentially, the new research is showing that we truly don’t have a very good understanding of both the brain and depression. What we do know, however, is that depression is a complex disorder. It’s not simply caused by one thing; it’s the result of many factors coming together in an individual at just the right time.

What this means is that the factors that cause depression are different for every person. You can’t just say, “Oh, it’s a chemical imbalance in the brain, so I should take some medication to fix it.” That doesn’t work because depression is much more than just a chemical imbalance. It’s also a social problem. It’s not just about chemicals; it’s about what happens in our lives and how we relate to others. It’s about stress, trauma, relationships and other factors that are outside of our control.

Another Step Forward

While this new research isn’t overly conclusive, it is a step towards finding better, more comprehensive, and safer treatments for depression. The most important thing to remember is that if you are struggling, there is always help and there is always hope. Seek out professional help and use this new research as a tool when discussing your mental health with your healthcare provider. Perhaps medication shouldn’t be the immediate solution for you. There are many other ways to treat depression, and it’s important that you find what works best for you. Most importantly, it’s important that you don’t try and get through it on your own.

Keep Reading: Eating a Certain Protein Is Related to Developing Depression : Study


  1. Major Depression.” NIMH
  2. The serotonin theory of depression: a systematic umbrella review of the evidence.” Nature. Joanna Moncrieff, et al. July 20, 2022.
  3. A chemical imbalance doesn’t explain depression. So what does?.” Science News Laura Sanders. February 12, 2023.
  4. The chemical imbalance theory of depression is dead – but that doesn’t mean antidepressants don’t work Christopher Davey for the Conversation.” The Guardian. August 3, 2022.