Feeling like going down the serotonin rabbit hole today? Let's go.
Serotonin is ancient.
What does that mean? It means that serotonin is believed to be one of the first signaling molecules ever to assist the developing nervous systems of primordial life forms on this planet. It was one of the 'founding fathers,' so to speak! While it may not have been present during the time of the primordial soup, it likely existed while we were still stuck in our single-cell incarnation. That's pretty ancient!
While this might seem like just a quirky aspect of serotonin, it is in fact intimately linked to what serotonin does for us today and why I refer to it as 'the molecule of everything' (in a tongue-in-cheek way!). But more on that later.
When you think of serotonin, what comes to mind? "Molecule of happiness," "feel-good hormone," "here-and-now chemical," or its association with depression?
Well, I bet my bottom dollar that it's one of the above. But what about aggression? Sleep? Sex? Movement? Appetite? Anxiety? Learning?
Check. Check. Check. And Check. And as it turns out, many, many more.
In fact, consider any behaviour or emotion, and serotonin likely plays a role in it.
It has been said for serotonin that it has an "omnipresent involvement in virtually every behaviour".
Remember how we discussed serotonin being an ancient molecule? Well, that's likely why its roles are so widespread. In simple terms, there has been ample evolutionary time for it to permeate the various mechanisms governing behaviour and neural functioning. It has had the chance to influence every nook and cranny of our nervous system.
That's why, when I hear "molecule of happiness," I think, no, it's more like "molecule of everything"! It is truly mind-blowing.
Long before serotonin became known as the "molecule of happiness," it was recognized as the molecule of aggression—or rather, the inhibition of aggression. Yes, you heard me right (for example, this paper is from 1968 while serotonin became the "molecule of happieness" in the late 1980's). Early research on animals, and later on humans, indicated that individuals with lower levels of serotonin were more prone to aggressive outbursts.
And then, as it annoyingly always happens in neuroscience, the plot began to thicken. As research progressed, it became clear that lower serotonin levels were associated with impulsive and escalating violent behavior. However, other, more socially accepted forms of aggression, such as defending one's territory, seemed to be linked to higher serotonin levels.
And, of course, as a seasoned neuro-geek, you’re probably already wondering: Yes, high levels of serotonin, but where exactly? You’d be right to ask that question, as it turns out that the relationship between serotonin and aggression varies depending on the brain structures, adding to the complexity.
And today, the quest continues still, sometimes generating more questions than it answers. However, we do learn a few things along the way.
Spoiler Alert: Serotonin plays a key role in establishing and maintaining the rules of social hierarchy (in both humans and other species).
To me this is particularly fascinating and so relevant for the practice of psychotherapy. As psychotherapists, we often have a keen eye for spotting the relationships of dominance and submission, within and without therapeutic relationship, and in society at large. I will dedicate a separate post to this fascinating topic and what it might mean for the practice of therapy.
To wrap up, let’s get practical: Have you ever tried supplements designed to enhance serotonin production?
If we were to ingest serotonin directly, it would be metabolised by enzymes in the gut. However, there are compounds that can cross the blood-brain barrier and eventually be converted into serotonin in the brain. One such compound is L-tryptophan, an amino acid present in food, which is used in the biosynthesis of serotonin.
But what are the effects of ingesting these molecules? Well there are some reports of it acting as a mild antidepressant or even affect the dominance in behaviour.
In my own experience, the only effect I ever noticed was on the quality of my sleep. This is because tryptophan is also involved in the production of melatonin, the hormone related to sleep—demonstrating just how complex the body’s systems are! If you decide to try it, please let me know about your experience. While the evidence will inevitably be anecdotal, a little serotonin self-exploration isn’t likely to cause harm. And remember to take my observations here with a pinch of salt!
In the meantime, serotonin continues to hold a solid top position in our collective imagination.
The formidable French writer Michel Houellebecq chose "Serotonin" as the title for his 2019 novel. I have not read it yet, but it sounds like a perfect summer read for a neuro-geek.
In a recent book, serotonin has also been cast as the hero against the villain, dopamine. This distribution of roles might be questionable, as serotonin and dopamine often work in concert.
It is funny how emotionally invested we become in brain chemicals—and in a full-circle twist, these very emotions about neurotransmitters are mediated by serotonin itself. After all, serotonin is the "molecule of everything" (tongue-in-cheek, remember)!
We discuss all this and much more in our upcoming book, Therapist's Guide Into the Brain. Co-written with Dr. Chad Luke and myself, it is due to be released in 2026 by Cognella.
I hope you enjoyed the read. For updates and more of the similar follow me on BlueSky or Twitter or subscribe to my mailing list.
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