What is serotonin?

Serotonin is a chemical messenger that has some important jobs in the brain and around the body. It is involved in controlling your mood. Low serotonin levels in the brain are thought to contribute to depression.

Serotonin is made by the body's nerve cells from a protein called tryptophan.

Serotonin works throughout the body, but mainly in the intestines, brain and blood. It works by sending messages between different body cells.

What is the role of serotonin?

Serotonin has many different roles. It helps control the muscles and how you move, and it influences appetite and how your bowels work. It is used to push out food from your digestive system (gut) when you vomit or have diarrhoea. It also helps your blood to clot and wounds to heal, and is involved in inflammation.

Serotonin is also very important in the brain. Serotonin is one of the natural body chemicals that controls your mood. It works with melatonin to help control when you sleep and wake up, as well as how you feel pain, wellbeing and 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
• digestive problems
• phobias
• depression
• anxiety disorders
• suicide thoughts or behaviours

While recreational drugs can increase serotonin in the short term, 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 is usually due to medicines or drugs that increase the amount of serotonin in your body. The symptoms of having too much serotonin is known as serotonin poisoning or 'serotonin syndrome', and it can be life threatening.

Serotonin syndrome might happen after your medicine dose has been increased, if you take too much (overdose), or if you take a combination of different medicines or drugs. It can also occur if you take antidepressant medicines along with some other prescription medicines, natural medicines or 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.

Serotonin symptoms usually go away around 2 to 3 days after you stop taking the medicines.

Serotonin syndrome can affect your brain, causing:

• confusion
• agitation
• restlessness

Serotonin syndrome can also affect your body, causing:

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

There are effects on your muscles:

• stiff muscles
• tremor
• overactive muscle reflexes

Sometimes high levels of serotonin are a sign of other medical conditions. Your doctor can assess you to find the reason for your serotonin syndrome.

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)

Most medicines that are used to treat depression work by increasing the amount of serotonin in your brain. They may also act on other chemical messenger pathways. Some examples include selective serotonin reuptake inhibitors (SSRIs), serotonin-noradrenaline reuptake inhibitors (SNRIs), tricyclic antidepressants and monoamine oxidase inhibitors.

To search medicines by active ingredient or brand name, use the healthdirect Medicines search feature.

When should I see my doctor?

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

Serotonin syndrome (too much serotonin) is usually treated in hospital. It's important to always follow your doctor's instructions when taking antidepressants. You should never mix prescribed medicines with other medicines or illegal drugs. If you are taking 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.

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 family and friends.
• Alcohol and Drug Foundation has resources on mental health, substance use and brain chemistry.
• Parkinsons 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 24 hours a day, 7 days a week.