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Serotonin has a wide variety of functions in the human body. People sometimes call it the happy chemical, because it contributes to well-being and happiness.
The scientific name for serotonin is 5-hydroxytryptamine (5-HT). It is mainly present in the brain, bowels, and blood platelets.
Serotonin is a neurotransmitter, and some also consider it a hormone. The body uses it to send messages between nerve cells.
Many investigations have looked at serotonin and what it does, but there is still a lot to learn.
In this article, we look at the role of serotonin in the body, uses of drugs that affect serotonin, side effects and symptoms of serotonin deficiency, and how to boost serotonin levels.
Serotonin is a result of tryptophan, a component of proteins, combining with tryptophan hydroxylase, a chemical reactor. Together, they form 5-HT, or serotonin.
The intestines and the brain produce serotonin. It is also present in blood platelets and plays a role in the central nervous system (CNS).
Occurring throughout the body, it appears to influence a range of physical and psychological functions.
Serotonin is also present in animals, plants, and fungi. For this reason, some people have looked at food as a possible source of serotonin.
Serotonin cannot cross the blood-brain barrier. This means that the brain must produce any serotonin that it needs to use. Treatments for depression and other mental health issues do not supply serotonin directly but trigger reactions that can boost serotonin levels in the brain.
However, research suggests that sources of serotonin in other areas, such as the digestive system, may work independently of serotonin in the brain. This could have implications for the treatment and prevention of various physiological conditions, such as bone degeneration.
As a neurotransmitter, serotonin relays signals between nerve cells and regulates their intensity.
Scientists believe it plays a role in mood and the CNS and affects functions throughout the body. It may have an impact on:
- bone metabolism
- cardiovascular health
- eye health
- blood clotting
- neurological disorders
However, the relationship between serotonin and many bodily functions remains unclear.
Scientists do not know precisely what causes depression, but one theory is that it stems from an imbalance of neurotransmitters in the body.
Normally, the body reabsorbs a neurotransmitter after it has transmitted its neural impulse. SSRIs stop the body from reabsorbing serotonin, leaving higher levels of serotonin to circulate.
Many people find SSRIs help relieve their symptoms, although the link between depression and serotonin remains unclear.
One problem for researchers is that, while they can measure serotonin levels in the bloodstream, they cannot measure its levels in the brain.
As a result, they do not know whether serotonin levels in the bloodstream reflect those in the brain. It is also impossible to know whether SSRIs can really affect the brain.
In 2015, one editorial called the use of SSRIs to treat depression “the marketing of a myth.”
Nevertheless, if scientists have not yet proven the serotonin theory of depression, SSRIs do appear to help many people.
Apart from depression, doctors may prescribe drugs that regulate serotonin levels to treat a number of other disorders, including:
- bipolar disorder
- post-traumatic stress disorder
- obsessive-compulsive disorder
- panic disorders
As with depression, some scientists have questioned whether serotonin is the only factor impacting these conditions.
SSRIs increase serotonin levels by preventing the body from reabsorbing serotonin neurotransmitters. Serotonin levels remain high in the brain, and this may elevate a person’s mood.
- citalopram (Celexa)
- escitalopram (Lexapro)
- paroxetine (Paxil, Pexeva)
- sertraline (Zoloft)
- vilazodone (Viibryd)
Adverse effects of SSRIs
SSRIs have some side effects, but these usually improve with time.
- nausea and vomiting
- restlessness and agitation
- diarrhea or constipation
- weight or appetite loss
- increased sweating
- blurred vision
- sleepiness or insomnia
- feeling shaky
- dry mouth
- low sex drive
- erectile dysfunction
- suicidal thoughts
In some cases, there may also be:
Rarely, taking too much of a drug that boosts serotonin levels or combining two such drugs can lead to serotonin syndrome. This is a potentially life threatening condition that may require emergency treatment.
SSRIs and suicide
A person who uses SSRIs for depression will not experience the benefits at once. At first, symptoms may worsen before improving. Anyone experiencing thoughts of suicide should seek help at once.
The FDA require all antidepressants to carry a black box warning about the danger of suicide during the initial stages of treatment, especially in people aged under 25 years.
If you know someone at immediate risk of self-harm, suicide, or hurting another person:
- Ask the tough question: “Are you considering suicide?”
- Listen to the person without judgment.
- Call 911 or the local emergency number, or text TALK to 741741 to communicate with a trained crisis counselor.
- Stay with the person until professional help arrives.
- Try to remove any weapons, medications, or other potentially harmful objects.
If you or someone you know is having thoughts of suicide, a prevention hotline can help. The National Suicide Prevention Lifeline is available 24 hours per day at 800-273-8255. During a crisis, people who are hard of hearing can call 800-799-4889.
According to the National Institute on Drug Abuse (NIDA), low levels of serotonin can lead to memory problems and a low mood.
These are symptoms of depression, although scientists have not confirmed a link between low serotonin levels and depression.
NIDA note that when people use certain recreational drugs, such as MDMA (ecstasy), the body releases large amounts of serotonin.
This can lead to serotonin depletion and a low mood, confusion, and other symptoms that last several days.
Animal studies have suggested that these drugs may damage the nerves that contain serotonin, with possible long-lasting adverse effects.
Some natural remedies may help boost serotonin levels in the body. These include:
- practicing meditation
- having light treatment, already in use for seasonal affective disorder
- doing regular exercise
- consuming foods that are high in tryptophans
There is not enough evidence to confirm that these methods can boost serotonin levels, but, in moderation, they are unlikely to be harmful.
Tryptophan is an amino acid that occurs in some foods. Some research has linked higher intake of dietary tryptophan to more positive mood scores, possibly because tryptophan bolsters serotonin levels.
Foods that may contain tryptophan include:
The body uses tryptophan to create serotonin. Eating foods that contain tryptophan may help support this process, but it does not mean that the body will necessarily absorb and use it. In addition, the amount of tryptophan in foods may be too low to make a difference.
In one study, a number of older people improved their scores on cognitive tests after taking tryptophan supplements for 12 weeks.
People should speak to a doctor before using any supplements, in case there is a risk of adverse effects. Supplements are available online.
Serotonin and the gut-brain axis
There is a growing interest among scientists in the idea that gut microbiota might influence the nervous system — including behavior, mood, and thinking — through a link known as the gut-brain axis.
If so, serotonin could provide the crucial link. This suggests that diet and the gut microbiota could play a role in preventing and treating conditions such as anxiety and depression.
However, more research is needed to confirm whether this is possible.
Serotonin, or the happy chemical, appears to play a role in various physical and psychological functions.
SSRIs are drugs that affect serotonin levels. They can help manage the symptoms of depression, although experts are still unsure exactly how it works.
Anyone considering taking a drug or supplement that affects serotonin levels should consult their doctor first to ensure it is safe for them to use.