Is Depression Caused by 'Chemical Imbalance'?

Depression is a mood disorder that people face at some point in their lives. It has been recognized by health professionals as the most common mental illness affecting millions worldwide. Individuals going through the condition experience persistent feelings of sadness and loss of interest. Depression causes individuals to behave, think, and feel differently, which leads to physical and psychological issues.

Various theories have been put forth as causes of depression. The father of psychoanalysis, Sigmund Freud, believed that depression (melancholy as it was then known) was a consequence of feelings of loss.

Other theories about the cause of depression thought of it to be a result of learned behaviors or that it was caused by negative interpretations of events that happened to a person. One of the most popular theories that emerged in the 1970s is that depression is caused by a chemical imbalance.

Chemical Imbalance Theory of Depression

The chemical imbalance theory was the outcome of the prevalent school of thought in psychiatry in the 1970s, which sought to understand all illnesses in purely biological terms. Two medications that were administered in the the 1950s for other medical reasons were shown to have positive effects on the patient's moods. Both medications, as a result of their chemical makeup, were shown to increase the levels of serotonin in the brain.

This led to the simple hypothesis that depression is simply the result of low levels of serotonin in the brain. However, studies on which this theory relied had the following constraints: sample sizes were small, the results were selectively reported, and the results could not be replicated in further studies.

Chemical Imbalance Theory: Flawed, Deceitful, or Outdated?

An umbrella review of several research papers on the topic of depression and anti-depressive medication released by Joanna Moncrief and colleagues effectively debunked the chemical imbalance theory as they found no evidence to support the claim that depression is caused by a disturbance in the brain's serotonin system.

The researchers looked into the brains of people with and without depression and compared the transporters and receptors of serotonin found in them. The researchers found no significant differences in the brains of those with or without depression.

So why is the chemical imbalance theory so popular today?

The chemical imbalance theory, despite very little conclusive evidence to support it either when first introduced or in the following decades of research, continues to be incredibly popular. In 2021, an estimated 23% of adults in the United States took medication for their mental health problems, with a majority of them for managing depressive symptoms, and an estimated 12% of the entire population in the United Kingdom took medication for depression.

Pharmaceutical companies looking to cash in on the simplistic sertonin hypothesis of the 1970s wasted no time in marketing the effectiveness of their products as a simple and effective solution to a complex problem. This marketing effort has been so effective that the chemical imbalance theory is still recognized as a possible cause of depression by the American Psychological association and the Australian Department of Health while being widely accepted by the public since the early 2000s.

Depression affects millions worldwide (Pexels Daniel Reche)

What Causes Depression?

Depression is a highly nuanced and individual illness, and no single, specific biological, social, or psychological factor can be considered to be the root cause. The list of things that correlate with depression include medications, biological gender differences, substance abuse, hyperthyroidism, abuse, trauma, stress, social isolation, inflammations, reactions to toxins, infections, brain injuries, gut health, genetic interaction with the environment, and many more.

Despite all the advancements in the mental health field, there still isn't a test that can accurately measure a single marker for depression. Despite the lack of evidence showing serotnin levels as a predictor for depression, there is a much stronger relationship between stress and depression.

Are Antidepressants a Waste of Time and Money?

Psychiatrists and other mental health practitioners have long dismissed the notion of the chemical imbalance theory as the sole reason for depression but still value and understand the importance of antidepression medication for patients. Antidepression medication has been shown to be 20% more effective in patients with depression symptoms as compared with patients who were given a placebo according to the National Library of Medicine.

Antidepressants are easily accessible as a treatment for those suffering from depression. They are effective for even the most severe forms of depression. Their efficacy is attributed to their ability to promote neuroplasticity. Neuroplaticity represents the brain's ability to heal and grow. Antidepressants work best in treating depression when combined with other therapeutic tools like therapy, exercise, ideal nutrition, social support, etc.

Is Chemical Imbalance Irrelevant for Depression?

Depression is a highly complex issue with many contributory factors. The chemical imbalance theories of the past that focused on the level of serotonin in the brains of patients have been disproved with the emergence of newer evidence about complex networks in the brain that process emotions and stress. Research focusing on social and cognitive behavioral aspects of relieving depression could lead to a clearer picture in future.