- Serotonin (5-hydroxytryptamine [5-HT]) is a biogenic amine naturally present in the body and stored primarily in the presynaptic nerve terminals of the CNS, enterochromaffin cells, and platelets.
- Serotonin functions in neurotransmission, intestinal motility, regulation of vasomotor tone and blood pressure, and platelet aggregation.
- Systemic levels in the circulation are normally low
- Serotonin syndrome (SS) is a spectrum of clinical signs caused by the effects of elevated serotonin levels.
- Ingestion of certain medications—at therapeutic (eg, adverse effect) or toxic doses—can result in SS (see Medications & Supplements That May Cause Serotonin Syndrome, and the handout, Agents Implicated in Serotonin Syndrome).
- SS can affect multiple body systems to varying degrees, depending on medication and dose ingested (see Table, below).
- Tryptophan is converted to 5-hydroxytryptophan (5-HTP) and then to serotonin.
- Accidental poisoning from ingestion of holistic supplements containing 5-HTP can result in significant SS.
- In humans, SS often occurs with coingestion of ≥2 drugs that alter serotonin metabolism via different mechanisms (eg, selective serotonin reuptake inhibitors [SSRIs], monoamine oxidase inhibitors [MAOIs]), although overdose of single agents has also been reported.1-3
- In veterinary medicine, most SS cases result from accidental ingestion or overdose of 1 drug.
- Depending on patient size and drug involved, ≥1 pill may be required to initiate clinical signs.