Serotonin is a beautifully named neurotransmitter that plays many important roles in our lives. There’s so much of it floating around in our bodies. Lots in our brains. Even more in our guts (along with that burrito you ate for lunch).

But that serotonin might not be doing what you think it’s doing. Serotonin is not a lever by which you can improve or dampen your mood. It is not the “happiness neurotransmitter”. In other words, serotonin is not pizza—my mood does not depend on the presence or absence of serotonin (unlike its dependence on the presence or absence of pizza). You can even have too much serotonin and get serotonin syndrome. Something that’s impossible with pizza.

Medical historians of the future will talk about the period of time around the end of the 20th century and the start of the 21st as a time when society generally subscribed to the myth that mental illnesses were caused by chemical imbalances. And then those historians will make some comment about that being a throwback to the medieval era when people thought health was dependent on balancing various internal fluids called “humors”. And the future historians might giggle a bit, maybe throw in a cautionary comment about the companies and doctors that fuelled the myth, then they’ll go play space golf.

The chemical imbalance view of mental illness is a medieval myth wrapped in a thin coating of contemporary sciencishness. As Thomas Insel, former director of the National Institute for Mental Health once described it back in 2011, it’s an “antiquated” view.

If you were thinking of getting the serotonin molecule tattooed on you so you have a little extra when you’re feeling low, that’s just not how serotonin or mental health works. If you’ve ever taken SSRIs, you probably have first-hand evidence of this. SSRIs boost serotonin levels when you start using them but it can take weeks to see a change in mood, if any at all. If improving mood was as simple as increasing serotonin, changes would happen much more quickly. The change would also be consistent amongst patients but nearly half of people see no change other than the side-effects, and clinical trials often find the placebo works as well as the SSRI. Serotonin is not to mental illness what insulin is to diabetes.  

That doesn’t mean serotonin isn’t awesome or you shouldn’t get that molecule tattooed on you. There are all sorts of actual things we know about this molecule inside of us:

• Recent research (like this study, or this study) suggests that increasing serotonin may increase neurogenesis. So extra serotonin is like fertilizer for your brain! This would also explain the benefits to mental health—mental illnesses like depression are associated with decreased neurogenesis—and it would also explain why it can take weeks to see any results—your brain takes time to grow (just like any other plant).
• Serotonin is like the Swiss army knife of the living world. Not only is it doing a variety of jobs around your body, but fungi and plants use it in all sorts of ways, it’s one of the reasons that wasp stings sting, even tiny amoeba use it (to give you diarrhea).
• Serotonin is an ancient tool. Many species of single-celled protozoa have, theoretically, used serotonin since protozoa were the most advanced beings on the planet. That was 1.5 billion years ago. (You can find a review here on the “Evolutionary ancient roles of serotonin”. Click the full text PDF link in the upper right hand corner of the page.) It’s kinda amazing that so many complex, modern lives end up revolving around simple signalling mechanisms that have played a key role in the evolution of life.

Even though serotonin isn’t the happy neurotransmitter it’s often presented as, and we’re still exploring how it works and what it does, we can say with certainty that it plays an amazing role in the living world. And that’s something we can all celebrate, whether it’s with a serotonin tattoo, or a necklace, or just enjoying all of the amazing things our bodies are doing for us right now.

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