1. Serotonin is only one player. There are hundreds of substances that act as neurotransmitters and that affect mood and mental state. These include amino acids (e.g. GABA, aspartate, glutamate), monoamines (e.g. serotonin, dopamine, norepinephrine, histamine), acetylcholine, nitric oxide, and a host of peptides (e.g. beta-endorphin).
2. The "chemical imbalance" hypothesis assumes a one-way mechanism, that is, brain chemistry affects mind. It's actually two-way, in that mind, the thoughts we choose to think over and over, can change brain chemistry and brain structure, just as exercising a muscle can change muscle shape and size. (Exercise can also effect brain chemistry, by, for example, the release of endorphins.) Indeed, "chemical imbalance" assumes a measure of "chemical balance" which has not been established.
3. Drugs sold in the US that increase levels of serotonin in the synapse (SSRIs: Selective Serotonin Reuptake Inhibitors) are used as antidepressants. But drugs sold in Europe that decrease levels of serotonin (SSREs: Selective Serotonin Reuptake Enhancers) are also used as antidepressants (e.g. Tianeptine/Coaxil).
"If depression can be equally affected by drugs that increase serotonin and by drugs that decrease it, it's hard to imagine how the benefits can be due to their chemical activity.4. Finally, evidence has been accumulating that, in most cases, SSRIs work no better than placebos in relieving mild to moderate depression. Here's one recent study, a meta-analysis or study of studies. It included 6 gold-standard, randomized, placebo-controlled trials:
The belief that antidepressants can cure depression chemically is simple wrong."
- Irving Kirsch (to Sharon Begley of Newsweek), researcher, professor, and clinical psychologist, author of "The Emperor's New Drugs: Exploding the Antidepressant Myth"
Antidepressant Drug Effects And Depression Severity, JAMA, 2010
"The magnitude of benefit of antidepressant medication compared with placebo increases with severity of depression symptoms and may be minimal or nonexistent, on average, in patients with mild or moderate symptoms."It's not fair to say that antidepressants work no better than placebos, implying that the placebo effect is not robust. The placebo effect is real, effective, enduring, and provides the foundation for a $10 billion antidepressant industry in the US.
Before signing off I should note two things that keep appearing in my reading as on a par with, and possibly better than taking antidepressants:
Adequate sleep. While antidepressants improved mood by 1.8 points on a 54-point scale used to gauge the severity of depression, better sleep improved mood by 6 points.
Exercise. Gretchen Reynolds in her New York Times article, Prescribing Exercise To Treat Depression, cites a 2011 study that found impressive rates of remission in a group of patients with major depressive disorder who walked for 30 minutes a day.