Depression and Serotonin

Debunking the Chemical Imbalance Theory

For decades, the public has been told that depression is caused by a "chemical imbalance" in the brain—specifically, a lack of serotonin. This theory suggests that taking Selective Serotonin Reuptake Inhibitors (SSRIs) fixes this deficiency, much like insulin treats diabetes.

However, this common belief is not supported by current research.

A landmark "umbrella review" of the evidence, as well as critical analyses of pharmaceutical advertising, have revealed a disconnect between marketing claims and scientific reality. These studies found no substantiated evidence that low serotonin levels are responsible for depressive symptoms.

What the Research Actually Says

The following articles are instructive in understanding the gap between public perception and scientific data:

• No Evidence Low Serotonin Causes Depression? (Medscape) – Discusses the major 2022 review by researchers at University College London, which found no consistent evidence linking serotonin levels to depression.

• Serotonin and Depression: A Disconnect (NCBI) – Highlights how direct-to-consumer advertising promoted the "chemical imbalance" narrative despite a lack of scientific consensus.

  
  

If It’s Not Serotonin, Why Do SSRIs Work?

If low serotonin isn't the cause of depression, why do millions of people feel better when taking SSRIs?

The answer likely lies in how these medications affect the brain's ability to process information. Rather than filling up a "low tank" of chemicals, medications aimed at increasing serotonin might help orient individuals to achieve more adaptive cognitions.

What Causes Anxiety? A Combination of Factors

A propensity for anxiety is rarely caused by a single thing; it is determined by multiple factors. The result is unique to each individual, with reactions running from alertness to excitation to panic. Key contributors often include:

• Early life experiences

• Specific emotional or physical trauma

• A genetically mediated sensitivity to nervous system excitation

  
  

This anxiety can also become attached to normal events, such as social situations, where there is no objective external threat. It can manifest as a feeling in the stomach; the gut contains many of the same neurotransmitters as the brain, which are activated through the vagus nerve in what is known as the gut-brain axis.

Neuroplasticity and Emotional Responsiveness

Current theories suggest that SSRIs may work by increasing neuroplasticity—the brain's ability to form new connections. This allows the brain to be more flexible and less stuck in rigid, negative thought patterns.

By subtly altering emotional responsiveness, these medications can create a "window of opportunity." They don't "fix" the depression directly; instead, they may dampen the intensity of negative emotions, allowing the person to engage more effectively in therapy and life changes.

Moving Beyond the "Fix" Mentality

Understanding that SSRIs do not treat a specific "deficiency" is empowering. It shifts the focus from a passive "cure" model to an active management model. The medication supports the biological system, making it easier for the person to do the psychological work required for recovery.