Serotonin Definition, Function & Effects of High/Low Levels

Serotonin Definition, Function & Effects of High/Low Levels

Serotonin Definition, Function & Effects of High/Low Levels

Serotonin is both a hormone and neurotransmitter. It is essential for regulating mood, movement, sleep & much more. What else does it do, and what happens when it’s balance? Read on to find out more!

Definition & Overview

Serotonin is an important signaling molecule throughout the brain and body. It is commonly known as the “happiness neurotransmitter” or the “happiness hormone” due to its prominent role in regulating mood.

Serotonin plays an important role in the brain, where its main job is to transmit messages between nerve cells. According to some scientific theories, serotonin is involved in all aspects of human behavior [1, 2].

However, brain serotonin makes up less than 2% of the total serotonin found in our bodies. Most serotonin (over 90%) is actually made, stored, and released by the gut. In addition, about 5-8% of serotonin is stored in platelets circulating in the blood [1, 3, 4].

As such, the roles of serotonin in the body are many and diverse. Research suggests that serotonin influences [4, 1, 3, 5, 2]:

  • Mood and emotions
  • Movement (motor function)
  • The sleep-wake cycle
  • Body temperature (thermogenesis)
  • Appetite
  • Bowel movements
  • Various gut functions
  • Blood clotting (platelet aggregation)
  • Constriction and relaxation of blood vessels (vasoconstriction and vasodilation)
  • Immune responses
  • Bone development
  • Heart function
  • Reproductive function & sexual behavior
  • Pain perception

What Does Serotonin Do?

Originally discovered in the 1940s, serotonin — also known as 5-hydroxytryptamine, or “5-HT” for short — is currently believed to play many pivotal roles in mood, behavior, gut, and overall optimal body function (homeostasis). So-called “imbalances” or other abnormalities in serotonin function have been linked with symptoms that may interfere with mental and physical health, and which can significantly impair quality of life [6, 7, 8].

According to some hypotheses and limited research, increasing serotonin levels may help with anxiety, depression, migraines, and constipation-predominant irritable bowel syndrome. However, more large-scale studies are needed [6, 7, 8].

Production and Removal

The majority of serotonin is made, stored, and released by cells in the gut lining (enterochromaffin cells). These cells make serotonin from the amino acid L-tryptophan, which is the main “building block”, or metabolic precursor of serotonin [9, 10].

Certain specific types of bacteria in the human digestive tract are believed to boost serotonin production in the gut. Gut flora actually balances tryptophan metabolism (via the kynurenine pathway), influencing the amount of L-tryptophan available for making serotonin. [11, 12].

However, serotonin produced by the gut cannot cross the blood-brain barrier. That is why brain cells must produce their own serotonin, either from L-tryptophan or 5-hydroxytryptophan (5-HTP), a byproduct of L-tryptophan [13, 14].

Conversely, excess serotonin and the brain and gut is “deactivated” by several different mechanisms. For example, proteins called serotonin transporters effectively “clean up” or “remove” (re-uptake) serotonin from neural synapses, and bring them back into neurons where it can be reused [15, 9].

Alternatively, serotonin that is released into the bloodstream either gets taken up (absorbed) by platelets, or is broken down (metabolized) in the liver and lungs by enzymes called monoamine oxidase (MAO-A), aldehyde, and alcohol dehydrogenase [3].


Serotonin is just one member of the “monoamine” family of neurotransmitters, which also includes other major neurotransmitters such as norepinephrine and dopamine. Researchers currently believe that all of these neurotransmitters work together to influence and regulate mood [16].

By extension, a person’s levels of each of these neurotransmitters may affect their mood.

For example, a meta-analysis of data from more than 50 different studies reported that artificially depleting the levels of these neurotransmitters can cause “low mood” and other related symptoms (this is typically done by depleting the body of the metabolic precursors needed to make these neurotransmitters, such as tryptophan or tyrosine). However, these effects were only observed in individuals who had certain pre-existing risk factors — such a prior diagnosis of depression, or a family history of depression disorders — and are not necessarily seen in otherwise healthy people [16].

Imbalances in the levels or relative activity of serotonin, dopamine, and norepinephrine have also been proposed to play a role in other common psychiatric conditions, such as bipolar disorder [17].

However, some researchers have proposed that combined low levels of these three neurotransmitters — and not just low serotonin alone — may be important for understanding how these mood disorders originally develop and progress [17].


In the pineal gland, serotonin is used to make melatonin, a hormone that synchronizes the body’s “biological clock” or circadian rhythm. When serotonin is low, that limits the amount of melatonin that can be made in the body, potentially interfering with the sleep-wake cycle [5].

Associated Health Conditions & Disorders

Note that when we talk about serotonin-associated disorders, it’s important to realize that these disorders are not necessarily directly due to serotonin levels or production per se.

Rather, they may instead stem from issues with serotonin reuptake, or the availability of certain serotonin receptors.

There are over 15 different receptor types discovered to date, including the well-known 5-HT1A, 5-HT2A, and 5-HT2C [18, 19, 20].

Additionally, the majority of studies covered in this article deal with associations only, which means that a direct cause-and-effect relationship hasn’t yet been conclusively established.

For example, just because depression has been associated with low serotonin in certain brain areas doesn’t mean that depression is actually directly caused by low serotonin. Data are lacking to make such claims.

Also, even if a study did find that low brain serotonin contributes to depression, serotonin levels are highly unly to be the only causative factor.

Complex disorders depression always involve multiple possible factors — including brain chemistry, environment, health status, and genetics — which may vary from one person to another, and which may interact in highly complex ways to cause any particular effect on health or well-being.

With this in mind, limited studies have linked abnormal serotonin levels with [2, 4, 1, 21, 22]:

  • Various mental health conditions and psychiatric disorders, such as depression, anxiety, aggression, obsessive-compulsive disorder (OCD), substance abuse, and schizophrenia
  • Irritable bowel syndrome (IBS)
  • Heart disease
  • Osteoporosis

Additionally, scientists believe serotonin connects the gut microbiome with the brain – forming the so-called “gut-brain axis.” Decreased diversity and stability of beneficial gut bacteria has been linked with serotonin-related health issues — especially in the elderly [23, 24, 25].

When To “Increase” Serotonin Levels?

any bioactive substance in the body and brain, serotonin levels need to be carefully balanced in order to ensure optimal overall health.

However, this important fact sometimes gets lost in the way that many people discuss certain popular health topics, such as serotonin and dopamine levels. Unfortunately, it’s often possible to come away with the impression that having “more” of these is always “better” — which is definitely not the case!

For example, elevated levels of serotonin can cause serotonin syndrome — a serious medical condition that can be potentially fatal [26, 27, 28].

Additionally, increasing serotonin levels can sometimes worsen the symptoms of other pre-existing conditions (such as OCD) [29, 30, 31].

Therefore, it shouldn’t be assumed that increasing serotonin levels or activity is necessarily always a good thing.

For this reason, it is crucially important to always talk to your doctor first before deciding to try any lifestyle changes or new supplements, as only a qualified medical professional can help you determine the most effective and safest course of treatment for you, your specific health needs and medical history.

Testing Serotonin

Serotonin that gets released into the blood gets rapidly broken down in the liver and lungs, to inactive metabolites (such as 5-HIAA) that are eventually excreted in urine [3].

This is why blood and urine typically contain trace amounts of serotonin. By extension, a person’s level of serotonin in these bodily fluids can sometimes be a useful diagnostic marker for serotonin-related abnormalities and health conditions. For example, larger quantities of serotonin in the blood/urine can be observed in people with serotonin-producing tumors (carcinoid tumors).

Nonetheless, there are a wide range of important limitations that reduce the reliability of urine tests when trying to “estimate” the actual levels of serotonin available in the brain. For example [32]:

  • Serotonin generally doesn’t cross the blood-brain barrier (BBB), meaning that the levels of serotonin in the blood don’t necessarily match up with the levels of active serotonin in the brain.
  • Even if serotonin did cross the BBB, it is released intermittently, and can be influenced by many different stimuli and other unpredictable factors. This means that a single measurement at a single point in time is not necessarily a reliable indicator of a person’s “normal” or “typical” levels of serotonin.
  • Furthermore, serotonin levels can vary quite a bit across different parts of the brain — so, once again, any single measurement might not necessarily say anything about how a specific part of the brain is using serotonin.
  • Finally, serotonin levels can vary for the same person from one day to another — so in reality, its levels would have to be tested multiple times on different days to get a reliable “snapshot” of a person’s overall levels of serotonin.

For these reasons, it is useful to remain skeptical about the use of urine serotonin levels to check for so-called “neurotransmitter imbalances.” While many companies that provide these tests state that the levels in urine directly and reliably correspond to brain neurotransmitter levels, research has repeatedly shown that this is not necessarily the case [32].

In addition, many of these companies have also been known to intentionally use extremely narrow reference ranges, without any scientific support whatsoever — often in order to sell supplements to their clients [33]!

By contrast, more reliable tests of serotonin levels include cerebrospinal fluid (CSF) tests, or measurements of serotonin in blood platelets.

This is because these measurements are either more “direct” measurements of serotonin in brain and nervous system (such as for CSF tests), or are measurements that are more “stable,” and have less sudden fluctuations over time (such as for platelet tests) [34, 35].

Ultimately, however, getting a PET scan is really the only “direct” way to accurately and reliably detect changes of serotonin production in specific areas of the brain [35].

Risks and Safety

any bioactive compound, serotonin (and the substances that potentially influence it) have the possibility of causing adverse side-effects and other potential risks and dangers.

Additionally, any substance or other factor that can influence serotonin levels also has the potential to have unpredictable and negative interaction with other dietary factors, supplements and medications, pre-existing health conditions, and other important health-related factors.

Therefore, always make sure to discuss any new supplements or lifestyle changes with your doctor first. Also make sure that he- or she is fully aware of any other relevant factors (such as special diets, current medications, or supplements) that may impact your health. The information in this post should never be used to replace conventional treatment.

Serotonin Syndrome

Excess serotonin may result in serotonin syndrome, which often results from adverse drug interactions, and which can be fatal [36].

MDMA, LSD, and other synthetic drugs may cause serotonin syndrome, and should not be taken without medical supervision or outside a psychotherapeutic environment [37].

>>>To learn more about serotonin syndrome, you can check out our detailed and comprehensive post on it here.

Drug Interactions

The use of St. John’s Wort, SAM-e, or lithium simultaneously with serotonergic drugs such as selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), or triptans can greatly increase the risk of serotonin syndrome, a life-threatening and potentially fatal condition [26, 27, 28].

Other Potential Risks

Abnormally heightened blood levels of serotonin (hyperserotonemia) is a consistent finding in individuals with autism. Relatedly, pregnant women with hyperserotonemia have been reported to be more ly to give birth to children with autism [38, 39].

Further Reading


What Serotonin Is and How It Regulates Body Functions

Serotonin Definition, Function & Effects of High/Low Levels

Jamie Garbutt / Getty Images

Serotonin (sometimes called 5-HT because of its chemical name, 5-hydroxytryptamine) is a substance that occurs naturally in your body. As a neurotransmitter, serotonin carries signals along and between nerve cells (called neurons). It’s found mainly in your intestines but also in your central nervous system (CNS), which includes your brain and your blood platelets.

Serotonin appears to affect and/or regulate a number of body functions, including the following.

You could think of serotonin's effects in your brain as its “starring role” in your body. Widely known for playing a major part in regulating moods, serotonin has been called the body's natural “feel-good” chemical, because it's involved in your sense of well-being.

Serotonin plays a role in your bowel function as well as in reducing your appetite as you eat. In addition, your intestines produce more serotonin if you eat something that’s irritating or toxic to your digestive system. The extra serotonin helps move the affected food along so it’s expelled from your body more quickly.

The platelet cells in your blood release serotonin when you have any kind of tissue damage, such as a cut. This results in vasoconstriction—a narrowing of the tiny arteries, or arterioles, in your circulatory system—which slows your blood flow as part of the blood-clotting process.

Studies have shown that bone density and serotonin are linked—specifically, high circulating levels of serotonin in the gut may be associated with osteoporosis.

In fact, research suggests that antidepressants, specifically selective serotonin reuptake inhibitors (SSRIs) are associated with decreased bone mineral density and increased fracture risk.

This isn't a reason to stop taking your SSRI, but rather, to have a conversation with your physician, especially if you have other risk factors, such as existing osteoporosis, a family history, or you smoke.

The increase in sexual desire that can accompany alcohol intoxication is believed to be due to low serotonin levels. On the other hand, decreased sexual desire can occur in people taking medications that produce higher-than-normal serotonin levels.

However, that’s only true when your serotonin level is within the normal range. What happens when it’s low? Perhaps the best-known condition believed to be associated with low serotonin levels is depression. Not surprisingly, increasing serotonin levels with medication has become a major part of depression treatment.

While there’s no one cause of low serotonin levels, it’s typically one of two reasons: your body doesn’t produce enough, or your body isn't using it efficiently, which can be due to having fewer or faulty serotonin receptors or breaking down and absorbing serotonin too quickly.

Nutritional and vitamin deficiencies may also play a part. Low levels of vitamin B6 and vitamin D have also been linked to low levels of serotonin. Tryptophan is an essential amino acid that must be obtained through the diet in order to produce serotonin.

Depression is associated with chemical imbalances in the brain, including low levels of serotonin (among others). Increasing the amount of serotonin in the brain appears to help brain cells communicate, which has the effect of reducing depression symptoms and improving mood. This finding is the basis for many drugs used in the treatment of clinical depression and other mood disorders.

One group of serotonin-based medications called selective serotonin reuptake inhibitors (SSRIs) is used to reduce the symptoms of moderate to severe depression by increasing the level of serotonin in the brain. SSRIs are the most commonly prescribed antidepressants worldwide.

When your brain cells send signals, they release neurotransmitters serotonin. To send the next signal, your cells must reabsorb and recycle the neurotransmitter they released in a process called reuptake. SSRIs help make more serotonin available in the brain by blocking that reuptake process.

Examples of SSRIs include:

  • Prozac (fluoxetine)
  • Paxil (paroxetine)
  • Zoloft (sertraline)
  • Celexa (citalopram)
  • Luvox (fluvoxamine)
  • Lexapro (escitalopram)
  • Viibryd (vilazodone)

Viibryd is NOT just an SSRI, but also a 5HT-1a partial agonist so it is not classified as purely an SSRI Trintellix is a similar drug.

Another group of serotonin-based medications for treating depression are known as serotonin-norepinephrine reuptake inhibitors (SNRIs). They work similarly to SSRIs in that they block the reuptake of serotonin, but they also work on norepinephrine, another neurotransmitter implicated in mood. As such, they are sometimes referred to as “dual-acting antidepressants.”

Examples of SNRIs include:

  • Effexor (venlafaxine)
  • Cymbalta (duloxetine)
  • Pristiq (desvenlafaxine)
  • Fetzima (levomilnacipran)

Two older types of antidepressants, tricyclics (TCAs) and monoamine oxidase inhibitors (MAOIs), also affect serotonin levels. However, they are prescribed less often today because their side effects are more problematic than those of SSRIs and SNRIs.

TCAs appear to block the reabsorption of serotonin and epinephrine which effectively increases the amounts available in the brain.

Examples of TCAs include:

  • Elavil (amitriptyline)
  • Norpramin (desipramine)
  • Asendin (amoxapine)
  • Anafranil (clomipramine)
  • Pamelor (nortriptyline)
  • Tofranil (imipramine)
  • Vivactil (protriptyline)
  • Surmontil (trimipramine)
  • Sinequan (doxepin)

MAOIs, on the other hand, block the effects of the monoamine oxidase enzyme which breaks down serotonin, epinephrine, and dopamine. By stopping the enzyme from breaking these neurotransmitters down, it effectively increases the amount available in the brain.

Examples of MAOIs include:

  • Marplan (isocarboxazid)
  • Parnate (tranylcypromine)
  • Nardil (phenelzine)
  • Azilect (rasagiline)
  • Emsam (selegiline)

These medications aren’t the only way to increase available serotonin. In fact, there are many ways to boost your levels naturally.

Many of the foods we eat naturally contain serotonin or other key nutrients, including tryptophan, vitamin B6, vitamin D, and omega-3 fatty acids, which the body needs to produce the neurotransmitter. A few good sources include:

  • Bananas
  • Turkey
  • Eggs
  • Oily, fatty, fish (salmon, tuna, mackerel) 
  • Nuts and seeds (walnuts and flaxseed)
  • Beans (chickpeas, kidney, pinto, black beans)
  • Leafy greens (spinach or kale)
  • Probiotic/fermented foods (kefir, yogurt, tofu)

Insufficient exposure to sunlight has also been associated with low levels of serotonin, which is why some people experience seasonal affective disorder (SAD) during the shorter, darker days of fall and winter.

While light therapy is an option (particularly in areas with little to no sunlight), you can also spend 10 to 15 minutes outside in the sunlight each day.

Doing so will work double-duty: You'll also get a boost of vitamin D, which plays a key role in serotonin production.

Regular exercise has been proven to boost serotonin in your brain, and some say it works just as well as serotonin-based medications.

How much and which type works best? The Department of Health and Human Services recommends at least 150 minutes of moderate-intensity cardio exercise each week plus two days of strength training exercises for all adults.

It's most important that you pick something you enjoy, so you're more apt to stick with it.

Massage therapy has increasingly been used in the treatment of depression. This is because massage has been found to promote the release of serotonin and decrease the stress hormone cortisol.

And you might not need a professional massage to reap the benefits. In a commonly cited study of pregnant women with depression published in the International Journal of Neuroscience, two 20-minute massage sessions given by their partners increased serotonin by 28% and dopamine by 31%.

Research has found that people with low serotonin also have deficiencies in some nutrients, so you might consider supplementation:

  • Pure tryptophan
  • SAMe (S-adenosyl-L-methionine)
  • 5-HTP
  • St. John's wort
  • Probiotics

Always talk to your doctor before taking any medication, supplement, or herbal remedy to treat low serotonin. Some medications and supplements can cause your serotonin levels to get too high, which can result in serotonin syndrome, also known as serotonin toxicity. Symptoms of serotonin syndrome can range from unpleasant to life-threating.

If you or a loved one experiences severe symptoms of serotonin syndrome, including sudden swings in blood pressure, seizures, or losing consciousness, call 911 or head to the emergency room.



Serotonin Definition, Function & Effects of High/Low Levels

Have you ever wondered what hormone is responsible for your mood and feelings? Serotonin is the key hormone that stabilizes our mood, feelings of well-being, and happiness. This hormone impacts your entire body.

It enables brain cells and other nervous system cells to communicate with each other. Serotonin also helps with sleeping, eating, and digestion. However, if the brain has too much serotonin, it may lead to depression. If the brain has too much serotonin, it can lead to excessive nerve cell activity.

It also helps reduce depression, regulate anxiety, and maintain bone health.

How Does Your Body Use Serotonin? 

Your body uses serotonin in various ways:


  • Serotonin is in the brain. It is thought to regulate mood, happiness, and anxiety. Low levels of serotonin are linked to depression, while increased levels of the hormone may decrease arousal.

Bowel Movements 

  • Serotonin is found in your stomach and intestines. It helps control your bowel movements and function.


  • Serotonin is produced when you become nauseated. Production of serotonin increases to help remove bad food or other substances from the body. It also increases in the blood, which stimulates the part of the brain that controls nausea.


  • Serotonin is responsible for stimulating the parts of the brain that control sleep and waking. Whether you sleep or wake depends on the area is stimulated and which serotonin receptor is used.

Blood Clotting 

  • Serotonin is released to help heal wounds. Serotonin triggers tiny arteries to narrow, which helps forms blood clots.

Bone Health 

  • Having very high levels of serotonin in the bones can lead to osteoporosis, which makes the bones weaker.

How Does Serotonin Impact Your Mental Health? 

Serotonin helps regulate your mood naturally. When your serotonin levels are at a normal level, you should feel more focused, emotionally stable, happier, and calmer.

What Problems are Associated with Low Levels of Serotonin? 

Low levels of serotonin are often associated with many behavioral and emotional disorders.

Studies have shown that low levels of serotonin can lead to depression, anxiety, suicidal behavior, and obsessive-compulsive disorder.

If you are experiencing any of these thoughts or feelings, consult a health care professional immediately. The sooner treatment starts, the faster you’ll see improvements.

What Problems are Associated with High Levels of Serotonin? 

Serotonin syndrome can occur when you take medications that increase serotonin action leading to side effects. Too much serotonin can cause mild symptoms such as shivering, heavy sweating, confusion, restlessness, headaches, high blood pressure, twitching muscles, and diarrhea.

More severe symptoms include high fever, unconsciousness, seizures, or irregular heartbeat. Serotonin syndrome can happen to anyone, but some people may be at higher risk. You are at a higher risk if you increased the dose of medication that is known to raise serotonin levels or take more than one drug known to increase serotonin.

You may also be at risk if you take herbal supplements or an illicit drug known to increase serotonin levels.

Questions to Ask Your Healthcare Team

If you suspect that your serotonin levels are too high or low, the first step is to speak with a health care professional. Consider asking your doctor:

  • Is my medication causing serotonin syndrome?
  • If I am experiencing feelings of depression, are my serotonin levels too low?
  • Are my levels of serotonin affecting any other aspects of my health?

Editor(s): Irina Bancos, M.D.

Last Updated: December 2018


Serotonin: 9 Questions and Answers

Serotonin Definition, Function & Effects of High/Low Levels

From the WebMD Archives

Serotonin acts as a neurotransmitter, a type of chemical that helps relay signals from one area of the brain to another. Although serotonin is manufactured in the brain, where it performs its primary functions, some 90% of our serotonin supply is found in the digestive tract and in blood platelets.

Serotonin is made via a unique biochemical conversion process. It begins with tryptophan, a building block to proteins. Cells that make serotonin use tryptophan hydroxylase, a chemical reactor which, when combined with tryptophan, forms 5-hydroxytryptamine, otherwise known as serotonin.

As a neurotransmitter, serotonin helps to relay messages from one area of the brain to another. Because of the widespread distribution of its cells, it is believed to influence a variety of psychological and other body functions.

Of the approximately 40 million brain cells, most are influenced either directly or indirectly by serotonin.

This includes brain cells related to mood, sexual desire and function, appetite, sleep, memory and learning, temperature regulation, and some social behavior.

In terms of our body function, serotonin can also affect the functioning of our cardiovascular system, muscles,and various elements in the endocrine system. Researchers have also found evidence that serotonin may play a role in regulating milk production in the breast, and that a defect within the serotonin network may be one underlying cause of SIDS (sudden infant death syndrome).

There are many researchers who believe that an imbalance in serotonin levels may influence mood in a way that leads to depression.

Possible problems include low brain cell production of serotonin, a lack of receptor sites able to receive the serotonin that is made, inability of serotonin to reach the receptor sites, or a shortage in tryptophan, the chemical from which serotonin is made.

If any of these biochemical glitches occur, researchers believe it can lead to depression, as well as obsessive-compulsive disorder, anxiety, panic, and even excess anger.

One theory about how depression develops centers on the regeneration of brain cells — a process that some believe is mediated by serotonin, and ongoing throughout our lives.

According to Princeton neuroscientist Barry Jacobs, PhD, depression may occur when there is a suppression of new brain cells and that stress is the most important precipitator of depression.

He believes that common antidepressant medications known as SSRIs, which are designed to boost serotonin levels, help kick off the production of new brain cells, which in turn allows the depression to lift.

Although it is widely believed that a serotonin deficiency plays a role in depression, there is no way to measure its levels in the living brain.

Therefore, there have not been any studies proving that brain levels of this or any neurotransmitter are in short supply when depression or any mental illness develops.

Blood levels of serotonin are measurable — and have been shown to be lower in people who suffer from depression – but researchers don't know if blood levels reflect the brain's level of serotonin.

Also, researchers don't know whether the dip in serotonin causes the depression, or the depression causes serotonin levels to drop.

Antidepressant medications that work on serotonin levels — SSRIs (selective serotonin reuptake inhibitors) and SNRIs (serotonin and norepinephrine reuptake inhibitors) — are believed to reduce symptoms of depression, but exactly how they work is not fully understood.

It can, but in a roundabout way. Un calcium-rich foods, which can directly increase your blood levels of this mineral, there are no foods that can directly increase your body's supply of serotonin. That said, there are foods and some nutrients that can increase levels of tryptophan, the amino acid from which serotonin is made.

Protein-rich foods, such as meat or chicken, contain high levels of tryptophans. Tryptophan appears in dairy foods, nuts, and fowl. Ironically, however, levels of both tryptophan and serotonin drop after eating a meal packed with protein.

Why? According to nutritionist Elizabeth Somer, when you eat a high-protein meal, you “flood the blood with both tryptophan and its competing amino acids,” all fighting for entry into the brain.

That means only a small amount of tryptophan gets through — and serotonin levels don't rise.

But eat a carbohydrate-rich meal, and your body triggers a release of insulin. This, Somer says, causes any amino acids in the blood to be absorbed into the body — but not the brain. Except for, you guessed it — tryptophan! It remains in the bloodstream at high levels following a carbohydrate meal, which means it can freely enter the brain and cause serotonin levels to rise, she says.

What can also help: Getting an adequate supply of vitamin B-6, which can influence the rate at which tryptophan is converted to serotonin.

Exercise can do a lot to improve your mood — and across the board, studies have shown that regular exercise can be as effective a treatment for depression as antidepressant medication or psychotherapy.

In the past, it was believed that several weeks of working out was necessary to see the effects on depression, but new research conducted at the University of Texas at Austin found that just a single 40-minute period of exercise can have an immediate effect on mood.

That said, it remains unclear of the exact mechanism by which exercise accomplishes this. While some believe it affects serotonin levels, to date there are no definitive studies showing that this is the case.

Studies show that men do have slightly more serotonin than women, but the difference is thought to be negligible.

Interestingly, however, a study published in September 2007 in the journal Biological Psychiatry showed there might be a huge difference in how men and women react to a reduction in serotonin — and that may be one reason why women suffer from depression far more than men.

Using a technique called “tryptophan depletion,” which reduces serotonin levels in the brain, researchers found that men became impulsive but not necessarily depressed.

Women, on the other hand, experienced a marked drop in mood and became more cautious, an emotional response commonly associated with depression.

While the serotonin processing system seems the same in both sexes, researchers now believe men and women may use serotonin differently.

Although studies are still in their infancy, researchers say defining these differences may be the beginning of learning why more women than men experience anxiety and mood disorders, while more men experience alcoholism, ADHD, and impulse control disorders.

There is also some evidence that female hormones may also interact with serotonin to cause some symptoms to occur or worsen during the premenstrual time, during the postpartum period, or around the time of menopause. Not coincidentally, these are all periods when sex hormones are in flux. Men, on the other hand, generally experience a steady level of sex hormones until middle age, when the decline is gradual.

In much the same way that we lose bone mass as we age, some researchers believe that the activity of neurotransmitters also slows down as part of the aging process.

In one international study published in 2006, doctors from several research centers around the world noted a serotonin deficiency in brains of deceased Alzheimer's patients.

They hypothesized that the deficiency was because of a reduction in receptor sites — cells capable of receiving transmissions of serotonin — and that this in turn may be responsible for at least some of the memory-related symptoms of Alzheimer's disease.

There is no evidence to show that increasing levels of serotonin will prevent Alzheimer's disease or delay the onset or progression of dementia. However, as research into this area continues, this could also change.

SSRI antidepressants are generally considered safe. However, a rare side effect of SSRIs called serotonin syndrome can occur when levels of this neurochemical in the brain rise too high.

It happens most often when two or more drugs that affect serotonin levels are used simultaneously.

For example, if you are taking a category of migraine medicines called triptans, at the same time you are taking an SSRI drug for depression, the end result can be a serotonin overload. The same can occur when you take SSRI supplements, such as St. John's wort.

Problems are most ly to occur when you first start a medication or increase the dosage. Problems can also occur if you combine the older depression medications (known as MAOIs) with SSRIs.

Finally, recreational drugs such as ecstasy or LSD have also been linked to serotonin syndrome.

Symptoms can occur within minutes to hours and generally include restlessness, hallucinations, rapid heartbeat, increased body temperature and sweating, loss of coordination, muscle spasms, nausea, vomiting, diarrhea, and rapid changes in blood pressure.

Although not a common occurrence, it can be dangerous and is considered a medical emergency. Treatment consists of drug withdrawal, IV fluids, muscle relaxers, and drugs to block serotonin production.

© 2008 WebMD, LLC. All rights reserved.


How to increase serotonin in the human brain without drugs

Serotonin Definition, Function & Effects of High/Low Levels

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