In brief
One of the brain's chemical messengers, called neurotransmitters. Many antidepressants are thought to work by changing the levels of serotonin and other brain chemicals.
- St John's wort can cause serious serotonin-related side effects when combined with certain antidepressants.
- Gut microbes produce many brain chemicals, but there is no conclusive evidence that serotonin made by gut microbes reaches the brain.
- For depression, antidepressants may start to help after 2 to 4 weeks, and the full effect can take 6 to 8 weeks.
How it works
Nerve cells pass messages to each other using chemicals called neurotransmitters, and serotonin is one of them. Antidepressants are thought to work by affecting the levels of several of these chemicals, including serotonin and noradrenaline, though this process is not fully understood.
Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed antidepressants in Australia. A rare side effect of some antidepressants is serotonin toxicity, also called serotonin syndrome. It is more common when taking more than one antidepressant, or other medicines such as opioids, migraine medicines or recreational drugs.
Connections
3 connections on the map. Select a topic to read its page.
Serotonin is linked with
- Gut and digestive system Emerging
Gut microbes produce many brain chemicals, but there is no conclusive evidence that serotonin made by gut microbes reaches the brain.
Source: Australian Academy of Science, Gut bacteria: the inside story
- Low mood and low motivation Supported
Antidepressants are thought to work by affecting brain chemicals such as serotonin and noradrenaline, though this is not fully understood.
Serotonin is part of
Serotonin is one of the brain's chemical messengers, called neurotransmitters.
Sources: healthdirect Australia, Antidepressants; Better Health Channel (Victorian Government), Nervous system
Medicines and supplements
General education only. Never start, stop or change a medicine without your prescriber.
Sources
Each connection above names its own source. See every source AskBioMap uses.
Summarised from healthdirect, the Better Health Channel, the NIH and the Australian Academy of Science. Sources read on 13 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.