The Happy Chemicals Series Part 3: Serotonin

More Than Just Happiness

When most people hear serotonin, they think of happiness. At least I did. When I heard serotonin, I thought of comfort, happiness, feeling good, and not much beyond that.

It is often called the happy chemical online, in conversations about mental health, and even in casual jokes. But the more I learned, the more I realized serotonin may be one of the most misunderstood chemicals we talk about.

Because serotonin is not just about happiness.

It helps regulate mood, sleep, digestion, appetite, memory, learning, emotional regulation, social behavior, and communication between the brain and body. And one of the most surprising things I learned? Most serotonin is not actually made in the brain.

Around 90–95% of the body’s serotonin is produced in the gastrointestinal tract (gut), while only a small portion is produced in the brain itself. That completely changed how I thought about it. I’ve dealt with gastrointestinal issues for years, and as I learned more about serotonin, some of those brain-body connections started making a lot more sense.

Because when people talk about serotonin, we usually talk about depression or mood. But serotonin is influencing far more than emotions. It is part of an incredibly complex communication system between the brain and body. Sometimes what we label as laziness, irritability, lack of motivation, emotional instability, or “something being wrong with us” can have incredibly complex biological processes happening underneath the surface.

The body is doing far more than we realize.

“Serotonin improves willpower, motivation, and mood.”
– Alex Korb

What Is Serotonin?

Serotonin, also called 5-hydroxytryptamine (5-HT), is a neurotransmitter.

A neurotransmitter is essentially a chemical messenger that allows nerve cells to communicate with one another.

Serotonin is made from tryptophan, an amino acid that we obtain from food.

Foods containing tryptophan include:

Turkey
Chicken
Eggs
Cheese
Salmon
Milk
Nuts and seeds
Beans
Tofu and soy products

But serotonin production is not as simple as eating turkey and suddenly feeling happier. Many things influence serotonin production and regulation, including:

Sleep quality
Nutrition
Physical activity
Sunlight exposure
Gut health
Stress levels
Hormones
Certain medications
Genetics

Serotonin exists within a larger system. It is not one switch that turns happiness on or off.

What Does Serotonin Do?

Mental health is rarely explained by one chemical alone. Depression, anxiety, trauma, stress responses, burnout, environmental factors, genetics, hormones, and life experiences all interact together.

Mental health is obviously incredibly complex, and no person is the same, so people will naturally have different experiences. But here are the main categories that Serotonin affects:

Mood Regulation – This is the role most people know. Serotonin helps regulate mood, emotional balance, and overall feelings of well-being. Lower serotonin activity has been associated with conditions such as:

Depression
Anxiety disorders
Irritability
Obsessive thoughts
Emotional dysregulation

Sleep Regulation – Serotonin also helps regulate sleep cycles. It serves as a precursor to melatonin, the hormone involved in sleep and circadian rhythms. Meaning serotonin helps create the chemical that helps regulate sleep.

Which means problems in one system can sometimes affect another.

Digestion and Gut Function – This was one of the most surprising things for me as I have had gastro issues for over a decade now. I have had surgery, etc. and to this day still struggle with issues related to this. But most serotonin is found in the gut, it helps regulate:

Intestinal movement
Digestion
Appetite
Nausea responses

It made me think differently about how often we separate physical health and mental health when they are deeply connected. The brain and body communicate constantly.

“In fact, 90 percent of serotonin and 50 percent of dopamine are actually produced in the gut.”
– Will Bulsiewicz

Memory and Learning – Serotonin also plays roles in:

Memory formation
Learning processes
Attention
Cognitive flexibility

Meaning it influences more than emotions—it can affect how we process information and in turn communicate, react, etc.

Social Behavior and Emotional Processing – Research suggests serotonin may also influence:

Social confidence
Impulse control
Emotional processing
Aggression regulation
Behavioral responses

Again, serotonin is not doing one job. It is helping coordinate an entire network.

“Many people stimulate that good serotonin feeling by trying to rescue others. Feeling like a hero is a reliable way to stimulate your serotonin.”
– Loretta Graziano Breuning

What Happens When Serotonin Is Low?

Potential symptoms associated with lower serotonin activity may include:

Depressed mood
Anxiety
Sleep disturbances
Fatigue
Irritability
Difficulty concentrating
Increased sensitivity to stress
Changes in appetite
Digestive issues

However, this is important: Experiencing these symptoms does not automatically mean someone has low serotonin. Many conditions overlap. This is one reason mental health and physical health assessments, and trying to determine the causing factor can become quite complex.

What happens when Serotonin is too high?

Yes. Excessively high serotonin levels—often due to medication interactions or certain medications—can contribute to serotonin syndrome, which can become serious and requires medical attention.

Possible symptoms include:

Agitation
Confusion
Rapid heart rate
Sweating
Tremors
Muscle rigidity
Fever

This is one reason medication changes and combinations should always be discussed with healthcare providers.

“It’s a long way from not having enough serotonin to thinking the world is stale.”
— Susanna Kaysen, Girl, Interrupted

Serotonin Receptors: It Gets Even More Complicated

In Part 2 we talked about dopamine receptors D1 through D5.

Serotonin has its own receptor families too. Scientists have identified seven major serotonin receptor families, known as 5-HT1 through 5-HT7, with multiple subtypes inside those groups.

Examples include:

5-HT1 receptors — involved in mood regulation, anxiety, and emotional processing

5-HT2 receptors — involved in mood, cognition, sleep, and perception

5-HT3 receptors — heavily involved in nausea responses and gut communication

5-HT4 receptors — involved in gastrointestinal function and memory

5-HT7 receptors — associated with sleep regulation and circadian rhythm.

The deeper I get into neuroscience, the more I realize how incredibly complex these systems really are. Serotonin is doing far more than regulating mood, even though that is usually what gets discussed in relation.

Stress, Recovery, and Why This Matters To Me

If I am honest, before sobriety I never thought about neurotransmitters. I never thought about consequences (until they happened). I never thought about what my body needs to be truly healthy. It rarely crossed my mind.

I was more focused on survival. I was thinking about making it through the day. I never thought about receptors, sleep cycles (except closing the bar down at 2A and going to work at 8A the next morning…. and taking cat naps during my lunch), brain chemistry, and long-term effects. Now I look back and realize how many things influenced the brain and body over time, from childhood until now:

Stress. Trauma. Sleep deprivation. Burnout. Substances. Recovery. Nutrition. Life experiences.

And it makes me wonder how many people blame themselves for things that are actually far more complicated. Not because biology excuses behavior.

It absolutely does not.

But understanding biology and what is happening in your own body and mind can help in the moment. You may still experience the negative side-effects, it will still be uncomfortable and difficult, but now at least I know why it’s happening. And now I know I will be okay and it will eventually pass. Before, it felt more like hopelessness, like I was broken. I truly thought there was no “fixing” me. I had fucked myself up too much, or so I used to tell myself. I had made that comment to many people.

Understanding creates options.

Final Thoughts

One thing this series keeps reminding me is how incredibly hard we are on ourselves. We expect ourselves to function perfectly while carrying stress, trauma, grief, burnout, sleep deprivation, health issues, and a thousand other things happening behind the scenes.

Then when we struggle, we assume it is a character flaw.

Maybe sometimes it is. But sometimes it is also a human brain doing its best with the circumstances it has been given.

Learning about these different chemicals has reminded me that there is so much happening beneath the surface that we never see. I always knew mental and physical health were connected. What I didn’t realize was just how complex that connection is—or how much chronic stress, trauma, and poor mental health can impact the body over time.

And while understanding the science does not solve every problem, it can help replace some judgment with understanding and empathy.

And sometimes that curiosity is where healing begins. That was my experience.

Thanks for reading this week — hope to talk to you next week! We will be going over Part 4: Oxytocin

Always enjoy when people chime in on the comments — please feel free if you have an experience, question, comment….. anything that you would like to say on the topic as long as it stays positive and kind. 😁

Blog: Detour From Hell; The Mind of a Hot Mess