...and why it's probably wrong.
Ok, the serotonin theory of depression may not be wrong. But it is definitely incomplete. One might ask why we use serotonergic drugs to treat depression if the theory behind it is wrong. A good question, but to this I say: because it worked.
This is post four of my series on depression. For previous posts on the etiology of depression, the pharmacotherapies for depression, and how depression is evaulated in the lab, please play link hopscotch! I've also got a very recent post on the serotonin system which can give you some more background.
The original antidepressants, the monoamine oxidase inhibitors and tricyclic antidepressants, were originally used to treat other diseases, such as tuberculosis and psychosis, and found to be effective for depression as a sideline. Did people know how they worked? Nope, but they appeared to work (though only in a subset of the population), and so they came into use. Some people might get up in arms about this, and yell about how we shouldn't use drugs unless we know how they work. But if we spent our lives doing that, no one would have ever made asprin. Or morphine. Heck, no one would have patented Ritalin. We know THAT Ritalin works, and we know what Ritalin does in the brain, but do we know why Ritalin calms down people with ADHD when it's really a stimulant? Not really, no. But it's still out there, because it works.
And the serotonin-based antidepressants do work in some people. Only in about 60% of patients at best, and at their best, they only perform 30% better than placebo. But the modern selective serotonin reuptake inhibitors (SSRIs) still work in a set of depressed patients, and they do so with far fewer side effects than pre-existing drugs. And what can I say, we haven't really got anything better yet. Except cocaine. That's a GREAT antidepressant, but it obviously has some issues.
So where did this serotonin theory of depression come from? And why is it flawed?