Ghosts, Goblins, and Serotonin: Boo!

In an earlier post, I noted that I thought a key opinion leader had contradicted himself across two articles regarding the role of serotonin in depression. One reader posted a comment that challenged my assertion, to which I reply via this post. The reader, “Alan,” stated, in part, that

He only said what he said -- that [serotonin] is clearly disordered and deficient in many if not most people with depression. And he is right. There's overwhelming evidence for that. (There's also great evidence for the therapeutic value of serotonergic interventions in depression, which he did not mention.) That's not to say that other things are not playing a role, or that serotonin is the sole problem area -- the "single fundamental neurobiological defect". He only said what he said. And this blogger is jumping all over him. Why?

Okay. Two issues here. One: Did the key opinion leader (Charles Nemeroff) contradict himself? Two: Is serotonin deficient in depression? This post will deal with issue two – people can read the old post and decide for themselves if Nemeroff’s statements were contradictory or if I was in error. You decide.

Part 1: Does a Serotonin Deficiency Cause Depression?

Let’s break this thing down to make it really simple to understand. Statement 1 from Alan: [serotonin] is clearly disordered and deficient in many if not most people with depression... There's overwhelming evidence for that.

Really? Drug companies certainly use serotonin to market their antidepressants, but is there solid evidence for a serotonin imbalance in depression? Actually, no.

Despite making excellent marketing copy, studies have found no consistent abnormality in serotonin in depressed people. Doubt me? Read this excellent article by Lacasse and Leo (published in PLoS Medicine) that describes the gap between the marketing of serotonin in depression and the scientific literature.

One quote from the PLoS Medicine article:

Consider the medical textbook, Essential Psychopharmacology, which states, “So far, there is no clear and convincing evidence that monoamine deficiency accounts for depression; that is, there is no ‘real’ monoamine deficit” [44]. Like the pharmaceutical company advertisements, this explanation is very easy to understand, yet it paints a very different picture about the serotonin hypothesis.

But since SSRI’s impact depression and also impact serotonin, depression must be due to a serotonin deficiency. Um, no. Again, I’ll leave it to Lacasse & Leo:

With direct proof of serotonin deficiency in any mental disorder lacking, the claimed efficacy of SSRIs is often cited as indirect support for the serotonin hypothesis. Yet, this ex juvantibus line of reasoning (i.e., reasoning “backwards” to make assumptions about disease causation based on the response of the disease to a treatment) is logically problematic – the fact that aspirin cures headaches does not prove that headaches are due to low levels of aspirin in the brain. Serotonin researchers from the US National Institute of Mental Health Laboratory of Clinical Science clearly state, “[T]he demonstrated efficacy of selective serotonin reuptake inhibitors…cannot be used as primary evidence for serotonergic dysfunction in the pathophysiology of these disorders” [12].

I could quote the article extensively, but I’d prefer that you read it yourself. Whether you have a scientific background or not, it’s easy to understand and it shows that the serotonin emperor is wearing no clothes. Don’t take my word for it. After you’ve read the article, if you’d like to do your own independent investigation on the topic, go ahead. Please report your findings showing a strong link between serotonin dysfunction and depression right here in the comment section. I’m waiting.

It is true that variations in the serotonin transporter gene can predispose people toward experiencing depression. I don’t deny that. And given that our understanding of the brain is still rather primitive, there may be some point where we figure out that serotonin plays a certain role in depression. But at this point, there is no evidence supporting a specific serotonin deficiency in depression. Again, please correct me if you disagree.

Part 2: Do SSRI’s Work?

Another piece from Alan’s comment:

There's also great evidence for the therapeutic value of serotonergic interventions in depression.

Like what? Try that about 80% of the drug effect is replicated by placebo – there is about a 20% difference in efficacy between placebo and antidepressant (Kirsch et al., 2002). Is that “great evidence” of efficacy? It’s more encouraging than 0% better than placebo, but I remain less than fully convinced. And about those sexual side effects and increased risk of suicidal thinking and suicide attempts… If depression was really due to poor serotonin function, then one would expect treatments that increase serotonin transmission would have a much stronger advantage over placebo.

I appreciate Alan’s comment as well as its timing. It is only appropriate on Halloween, I should discuss the serotonin-depression link, as it is about as well supported scientifically as many of the ghost stories often told on such a holiday.