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The understanding of depression has changed in remarkable ways over the past century or so. From the “melancholia” of Freud’s time to electroshock “Cuckoo’s Nest” conceptualizations, doctors, writers, and sufferers have struggled to capture the best set of words and images to convey this debilitating illness. Is the “chemical imbalance” theory, and in particular the role of serotonin, simply the latest in this series of efforts to explain this set of symptoms? And is the popularity of this explanation waning? And if so, why?

A brief internet search yields mixed results. Some popular websites, such as “Buzzle” or “Psyweb,” continue to report that depression (or more specifically “Major Depressive Disorder”) results from a serotonin deficiency. However, other websites report research indicating that the correlations do not hold up: major depression may occur in people with high serotonin levels, and people with low serotonin levels do not consistently report depressive symptoms. How can therapists and their clients understand this apparent conundrum?

A Quick Review

Serotonin is a type of naturally occurring chemical our body produces called a neurotransmitter. There are a number of different neurotransmitters; serotonin is not the only one associated with mood and emotional/psychological functioning. Dopamine and norepinephrine, also neurotransmitters, have been studied with regard to their role in mental illnesses. Tryptophan, an amino acid our body does not produce, is needed to manufacture serotonin.

Neurotransmitters do exactly what it sounds like they do: they transmit neurological messages or information from one part of the brain to another. Interestingly, however, the lion’s share of serotonin found in the human body is not found in the brain: in healthy, non-depressed people, approximately 90 percent of the body’s serotonin is found in the digestive system and in the platelets (the component of the blood associated with clotting and healing). While blood levels of serotonin can be measured, “brain levels” of this chemical cannot be measured in a living person. Thus gaining an accurate sense of serotonin availability is limited.

The current story regarding serotonin and depression goes somewhat like this: for some reason, in some people, instead of flowing freely and transmitting messages as it is supposed to, the body produces serotonin but then “gobbles it up.” Serotonin is absorbed in the synapses and unavailable to do its job. This, it is theorized, results in depression: not exactly a serotonin imbalance or a deficiency, but a lack of availability when and where it is needed.

The Problem?

One concern regarding the serotonin story is that it was promoted so thoroughly by the makers of the medications that prevented the reuptake of serotonin. Once the antidepressants known as serotonin specific reuptake inhibitors (SSRIs) were available, the explanation of depression changed to match what the medication did. Prior to the availability of Prozac or Zoloft, serotonin reuptake was not considered a problem by psychiatrists treating depression. For some researchers and critics, this was seen as a “tail wagging the dog” issue—the actions of an available medication became the dominant description of the condition.

An additional concern was mentioned above: studies have shown that the correlation between serotonin levels and depression does not hold up. Sometimes, for some people, low serotonin levels translate into the development of depressive symptoms, but not consistently. Some depressed people have high serotonin levels. Add to the picture that serotonin “overdose” or toxicity is possible, causing severe physical and psychiatric symptoms, and the situation becomes even more complex.

On the other hand, the improvements of SSRIs over the previous generation of antidepressants are undeniable: significantly fewer side effects and less toxic in the case of an overdose, the SSRIs represent a definite step forward in the medical treatment of depression.

Even more importantly, some people suffering from depression experience truly life-changing relief. Anecdotally, psychotherapists and psychiatrists have reported countless success stories in which patients describe “the black cloud lifting” and a level of functionality never before attained now coming easily.

The Bottom Line?

One thing that is known is that serotonin is a critical neurotransmitter that plays a role in regulation of a number of physical, emotional, and psychological functions, including but not limited to sleep, mood states and emotions, milk production for lactating women, appetite, memory, libido, and temperature regulation. Clinical studies and anecdotal reports support the theory that at least for some people in some cases serotonin levels are an important piece of the puzzle in terms of treating depression. While clearly not as simple as the chemical imbalance theory would have us believe, we can’t throw the serotonin baby out with the bath water either.

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