Serotonin syndrome is a condition caused by an excess of serotonin in the brain. The effects of serotonin syndrome may progress from headaches, dizziness and vomiting, to coma and death.

Symptoms affect three major nervous systems:

1. autonomic nervous system: increased body temperature, sweating, hypertension, increased heart rate, nausea, diarrhoea;
2. somatic nervous system and muscles: muscle twitching, alternating contraction and relaxation (e.g. jaw, giving rise to teeth chattering), hyperreflexia, rigidity, tremor;
3. cognitive functioning of the brain: confusion, agitation, headache, coma.

Serotonin syndrome is generally caused by interactions between serotonergic drugs, for example by concurrent use of MAOIs and SSRIs. It is also caused by an overdose of SSRIs.

See also: Ecstasy, Dextromethorphan, Tramadol es:síndrome de serotonina