What is serotonin?

Serotonin is a chemical messenger (neurotransmitter) that plays important roles in your brain and around your body. It works by sending messages between body cells.

It is involved in controlling your mood. Low serotonin levels in the brain are thought to contribute to depression.

The scientific name for serotonin is 5-hydroxytryptamine (5-HT).

Serotonin is made by nerve cells from a protein called tryptophan. Tryptophan is found in many foods. Your body breaks down these foods to make serotonin.

Serotonin works throughout your body, but mainly in the:

• intestines
• brain
• blood

What is the role of serotonin?

Serotonin plays a role in many different body functions including:

• helping to control your muscles and how you move
• influencing appetite
• bowel function
• pushing out food from your digestive system (gut) when you vomit or have diarrhoea
• blood clotting
• wound healing
• inflammation

Serotonin is also very important in your central nervous system. It is one of the natural body chemicals that controls your mood. Serotonin can be converted into melatonin. This helps control when you sleep and wake up. Serotonin can also affect:

• how you feel pain
• learning and memory
• sexual desire

Medicines that increase serotonin levels can help with:

• depression
• anxiety
• obsessive-compulsive disorder
• social anxiety disorder
• panic disorder
• post-traumatic stress disorder (PTSD)

What happens if I have too little serotonin?

Low levels of serotonin are related to many conditions including:

• sleep problems and fatigue
• mood swings
• digestive problems
• phobias
• depression
• anxiety disorders
• suicide thoughts or behaviours

Many recreational drugs can increase serotonin in the short term. But over time, they can reduce the levels of naturally occurring serotonin — this can lead to depression.

What happens if I have too much serotonin?

Having too much serotonin usually happens because you are taking medicines or drugs that increase the amount of serotonin in your body. Having too much serotonin is known as 'serotonin toxicity' or 'serotonin syndrome'. Severe serotonin toxicity can be life-threatening.

What causes serotonin toxicity?

Serotonin syndrome might happen:

• after your medicine dose has been increased
• if you take too much medicine (overdose)
• if you take a combination of different medicines or drugs

Serotonin toxicity can also occur if you take antidepressant medicines along with:

• other prescription medicines
• some natural medicines
• recreational drugs (such as ecstasy, cocaine, and amphetamines)

All of these can increase serotonin levels in the body and put you at risk of serotonin syndrome.

What are the symptoms of serotonin toxicity?

Serotonin syndrome can affect your brain, causing:

• confusion
• agitation
• restlessness
• anxiety

In more severe cases it can also cause seizures.

Serotonin syndrome can also affect your body, causing:

• high temperature
• high blood pressure
• sweating
• fast heart rate
• diarrhoea
• shivering
• dilated pupils

There are effects on your muscles:

• stiff muscles
• tremor
• overactive muscle reflexes
• being overly flexible

Sometimes high levels of serotonin are a sign of other medical conditions such as alcohol withdrawal and hyperthermia (heatstroke). Your doctor can assess you to find the reason for your serotonin syndrome.

Serotonin symptoms usually go away a few days after you stop taking the medicines.

CHECK YOUR SYMPTOMS — Use the Symptom Checker and find out if you need to seek medical help.

How can I adjust my serotonin levels?

There are ways to naturally increase serotonin levels in your body, through lifestyle measures such as by:

• getting more exposure to outdoor sunlight
• doing plenty of exercise
• eating foods that contain a substance known as tryptophan (such as nuts, eggs, cheese, red meat, turkey, salmon, tofu and pineapple)

People with depression are thought to have low levels of serotonin. Most medicines that are used to treat depression increase the amount of serotonin in your brain.

They may also act on other chemical messenger pathways. Examples of antidepressants include:

• selective serotonin reuptake inhibitors (SSRIs)
• serotonin-noradrenaline reuptake inhibitors (SNRIs)
• tricyclic antidepressants (TCAs)
• monoamine oxidase inhibitors (MAOIs)

Read more about antidepressant medicines.

LOOKING FOR A MEDICINE? — To search by brand name or active ingredient, use the Medicines information search feature.

When should I see my doctor?

If you have signs or symptoms of too much or too little serotonin it is important to see a doctor.

For advice and to connect to local mental health services, call Medicare Mental Health on 1800 595 212. Check the operating times.

Severe serotonin syndrome (too much serotonin) is life-threatening and needs treatment in hospital.

It's important to always follow your doctor's instructions when taking antidepressants. Never mix prescribed medicines with other medicines or illegal drugs. If you take medicines that are prescribed by more than one doctor, ask your doctor or pharmacist for advice.

Never stop taking antidepressant medicines without talking to your doctor first.

FIND A HEALTH SERVICE — The Service Finder can help you find doctors, pharmacies, hospitals and other health services.

Resources and support

For more information and support visit one of these websites:

• Headspace has a fact sheet on antidepressants (including those that work on serotonin) for young people, their families and friends.
• Alcohol and Drug Foundation has resources on mental health, substance use and brain chemistry.
• Parkinson's NSW has information on natural body hormones, and how they work.

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with you 24 hours a day, 7 days a week.

Languages other than English

Embrace Multicultural Mental Health offers mental health resources and personal stories translated into more than 30 languages.

You can find translated information about medicines on the NPS MedicineWise website.

Information for Aboriginal and/or Torres Strait Islander peoples

• 13YARN — to talk with Aboriginal and/or Torres Strait Islander Crisis Support. Call 13 92 76.
• NPS MedicineWise — About Depression Medicines; Information for Aboriginal and Torres Strait Islander people.