You’ve probably heard of serotonin before, but can’t say exactly what it as and how it works. “Most people know serotonin as ‘the happy chemical’ because low levels are associated with depression,” says Lynn Jonen, psychologist and clinical director of Sierra Tucson. So let’s start there.

Why Is Serotonin Called The Happy Chemical?

This is one of those oversimplifications that stick. The real story is, there’s a connection between serotonin and mood, but it’s kind of like the chicken and the egg. Scientists are not sure if low levels of serotonin can cause depression; or if depression can cause low levels of serotonin.

Alright, Let’s Back Up: What Is Serotonin?

The easiest way to think about it is that serotonin is a chemical communicator that carries signals from one part of the brain to another. It’s kind of the busybody of your whole body. It has a big role in consciousness, attention, cognition, and emotion; but it regulates a bunch of other systems throughout your body too.

It’s usually referred to as a neurotransmitter—because it’s a messenger of information between neurons—but serotonin pulls double duty as a hormone, a chemical released into the bloodstream that sends messages to various body parts, including the gut and blood platelets.

What Does Serotonin Do in the Brain?

Serotonin has a number of psychological functions. Of the approximately 40 million brain cells in our heads, it’s estimated that serotonin impacts just about every single one of them, either directly or indirectly.

  • Cognition: High levels of serotonin have been shown to boost cognitive abilities including memory and learning speed.
  • Autonomic nervous system function: Studies have shown that serotonin enhances our autonomic nervous system function or fight-or-flight response.
  • Mood: It’s widely believed that serotonin in the brain helps to reduce anxiety and depression, regulate our emotions, and contribute to and overall sense of well-being. Think of it like a natural mood stabilizer.

So, Explain. How Does Serotonin Impact Mood? And How Is That Related to Mental Health?

The unsatisfying answer is researchers aren’t sure. While they can measure serotonin levels in the bloodstream, it’s impossible to measure them in the brain of a living person.

“We can’t say that serotonin impacts mood in a particular way,” says Jonen. “A lot of what we know is by inference and observation. We’ve noticed that when serotonin levels are high, mood improves. But there are lots of other chemical processes happening in the body—it might not be a one-to-one relationship. We don’t know if people who are depressed stop making serotonin, if low levels of serotonin lead to depression, or if there are other factors that cause both depression and low serotonin.”

Other potential causes include faulty serotonin receptors on cells or a lack of tryptophan, the amino acid from which serotonin is made.

Despite these lingering question marks, it is clear from research that balanced serotonin levels often lead to calm, focused, happy, and stable moods. When levels dip too far, well let’s just say, it’s a different story. Low serotonin levels are mostly commonly associated with depression, as well as anxiety, panic disorder, obsessive-compulsive disorder, and excessive anger.

What Do Drugs That Have Serotonin Do?

It isn’t as simple as “taking” serotonin. It’s about encouraging our bodies to re-balance the amount of serotonin in our brain. Researchers believe that the most common antidepressants SSRIs (selective serotonin reuptake inhibitors like Prozac and Zoloft) and SNRIs (serotonin and norepinephrine reuptake inhibitors like Effexor and Cymbalta) work by blocking reuptake during cells’ communication process.
“Reuptake inhibitors add serotonin indirectly by preventing the first cell from taking serotonin back when the second cell doesn’t pick it up during communication,” says Jonen. “We’re hoping if we make more serotonin available to the brain between the gaps of cells, it will decrease depression. Theoretically, that’s how it works. But since we can’t measure serotonin levels in the brain we need to address depression from many different angles.”
In fact, the success rate of SSRIs and SNRIs is quite low. Studies estimate that 50-65 percent of people with depression will see some improvement from antidepressants.

Can You Raise Your Serotonin Levels?

Absolutely, says Jonen. “Any perception that comes into your body—whether it’s a drug, food, or light—turns into neuropeptides, chemical messengers.” Here are a few that influence serotonin.

  • Diet: One of the best things we can do to naturally boost the levels of serotonin in our systems is to eat foods that with tryptophan. While there’s no food that will directly increase our levels of serotonin, protein-rich foods, such as turkey, bananas, eggs, salmon, and cheese contain high levels of tryptophan that give our bodies the raw material they need to make enough serotonin.
  • Light therapy: We already know that light has the ability to affect mood thanks to the existence of seasonal affective disorder. There are also studies to support that serotonin levels are higher in summer and lower in winter. Spend at least 15 minutes a day outside or consider investing in a light therapy box.
  • Exercise: Exercise has also been shown to increase serotonin levels. Cardio in particular—such as running, aerobics, and swimming—is particularly effective.
  • Supplements: A number of supplements appear to help us create more serotonin, including vitamin  B-6, 5-HTP, pure tryptophan, and probiotics.

[See ways to boost Serotonin levels naturally]

Your Body Also Makes Serotonin On Its Own, Right? How?

It’s estimated that 90 percent of serotonin is made in the digestive tract. The rest is found in your central nervous system, including—you guessed it—the brain. 

But serotonin doesn’t just appear out of thin air or body matter, as it were. Creating the good stuff requires a biochemical conversion process with tryptophan. (Yes, the same amino acid in turkey that makes you so sleepy after Thanksgiving dinner.) Cells that make serotonin use tryptophan—a building block for proteins—along with tryptophan hydroxylase, a chemical reactor, to form serotonin. This is why eating tryptophan-rich foods is a great way to naturally increase serotonin.

When Is Serotonin Released?

Whenever you laugh at a movie, your body releases serotonin. That’s just one example of the chemical communicator in action. It’s also released during any number of events that involve the systems it affects, including blood clotting and nausea. 

How does it all work? Think back to high school biology class. Our bodies are made of a collection of cells. But because cells aren’t directly connected, they need a way to talk with one another—that’s where serotonin comes in. 

“Chemical communicators like serotonin are picked up by cells to fire electric communication signals,” says Jonen. “Messages need to pass from cell to cell to indicate what we should think or feel or even to rebalance a part of the body.” After the serotonin is released, it’s reabsorbed and recycled by cells in a process called reuptake.

What Happens When There Is Too Much Serotonin In The Brain?

Despite serotonin’s positive associations, you can have too much of a good thing. If serotonin levels become excessive—most commonly when an antidepressant is improperly mixed with another serotonin-related drug like triptan migraine medications, over-the-counter cold medicines that contain dextromethorphan, or recreational drugs like cocaine and LSD—some people experience a rare condition called serotonin syndrome. Its symptoms run the gamut, including agitation, confusion, rapid heart rate, high blood pressure, dilated pupils, loss of muscle coordination or twitching muscles, heavy sweating, nausea, and diarrhea. More severe symptoms, such as seizures, high fever, and loss of consciousness, can even be life-threatening.

What Other Systems Rely On Serotonin? 

A whole host of systems depend on serotonin. In fact, it touches just about every part of us. Here are some of the biggest ways it keeps our bodies running.

  • Digestion and appetite: With such a large percentage of serotonin made and found in the gut, it makes sense that it plays a role in controlling our bowel movements. If we eat something that’s upsetting to our GI tract, extra serotonin is produced to help move the food along more quickly. And if serotonin blood levels rise enough, it stimulates the part of the brain that flags nausea. But it doesn’t stop there: serotonin in the brain also acts as a neurotransmitter to tell us when to quit eating.
  • Blood clotting: The next time you accidentally slice your finger cutting an avocado and it stops bleeding, you have serotonin to thank. When they’re alerted to tissue damage, your blood platelets release serotonin, which causes tiny blood vessels to constrict and form blood clots.
  • Sexual function: Less is known about the link between serotonin and sexual function, but it appears that high levels of serotonin actually inhibit sexual desire and function. “This is why one of the side effects of SSRIs [selective serotonin reuptake inhibitors and the most common class of antidepressant] can be sexual dysfunction,” says Jonen.
  • Bone health: A few studies have linked very high levels of serotonin in the gut to weaker bones, increased risk of fracture, and osteoporosis. 
  • Sleep: As a neurotransmitter, serotonin stimulates the section of the brain that controls the sleep wake cycle. Serotonin is also a chemical precursor to melatonin, the main sleep hormone.

The bottom line is serotonin is more than just the “happy chemical.” It’s vital to almost every system in our bodies. And while research has shown it is linked to mood regulation, it’s still not clear exactly how. And, it’s not as simple as upping your serotonin to feel better.

Last Updated: May 7, 2021