Serotonin or 5-hydroxytryptamine (5-HT) is a neurotransmitter that binds to 5-HT receptors in the central and peripheral nervous systems. Serotonin is an example of an inhibitory neurotransmitter that has general sedative effects on the brain and counteracts the effects of stimulants such as caffeine, for example.

Adequate serotonin levels are needed to maintain a stable and balanced mood. Serotonin is mainly found in the gastrointestinal tract, the platelets and the central nervous system of animals and is thought to contribute to a sense of well being and happiness.

Several drugs are available that modify the 5-HT system and examples include:

Antidepressants

Several types of drug are used to modify the 5-HT system in the treatment of depression. Monoamine-oxidase inhibitors (MOAIs) are drugs that prevent the breakdown of serotonin by the enzyme monoamine oxidase.

Selective serotonin reuptake inhibitors (SSRIs) are another form of therapy that prevents the reuptake of serotonin from the synaptic cleft so that it remains available to target nerve cells. Tricyclic antidepressants (TCAs) inhibit the re-uptake of both serotonin and norepinephrine from the synaptic cleft, therefore increasing the availability of these neurotransmitters.

Compared with MAOIS and TCAs, the SSRIs are more selective and are associated with fewer side effects. Some of the more commonly used SSRIs include fluoxetine, fluvoxamine, citalopram and escitalopram.

Antiemetics

One form of antiemetic is the 5HT3 receptor antagonist, which stops serotonin form binding to its receptor in the central nervous system and gastrointestinal tract. These drugs are used to prevent nausea and vomiting after surgery or after the use of cytotoxic drugs. Examples include ondansetron, granisetron and tropisetron.

Triptans

Triptans such as sumatriptan and rizatriptan are 5HT1B/1D agonists and stimulate the receptor in a similar way to serotonin. These agents relieve migraine and cluster headaches.

Psychedelic drugs

Recreational drugs such as psilocin, mescaline and LSD act specifically on the 5HT2A receptor.