Serotonin syndrome is the consequence of excessive stimulation of the central nervous system and peripheral serotonin receptors. It can arise due to taking medication, illegal drugs or dietary supplements, and normally occurs when two drugs that affect serotonin levels are taken at the same time i.e. taking migraine medicine alongside antidepressants.

Carcinoid tumors can cause excessive levels of serotonin. These are cancerous and are commonly found in the GI tract. The tumors cause too much serotonin to be released. Most carcinoid tumors have no symptoms, and so they are often found when tests or procedures are carried out for other conditions.

Serotonin syndrome leads to excessive nerve activity. Symptoms can occur within a few hours of the substance, inducing the condition, being taken. It is potentially life-threatening, and signs and symptoms include:⁷

If the case is severe then serotonin syndrome can be life threatening. It can lead to high fever, irregular heartbeat, seizures and unconsciousness.

Serotonin syndrome cannot be diagnosed by a single test, and as many other conditions share similar symptoms, a health care provider will attempt to rule these out before diagnosing serotonin syndrome.

If diagnosed, treatment will focus on attempting to restore normal serotonin levels. If symptoms are minor then stopping the medication that began the problem could be enough to make the symptoms go away after a few days.

More extreme forms of serotonin syndrome may require treatment in hospital. Depending on the degree of the symptoms, various medications can be given to relax or paralyze the muscles, control heart rate and blood pressure and in some cases block the production of serotonin.

Oxygen can also be given as can fluids intravenously, in order to maintain normal levels of oxygen in the bloodstream and to treat fever and dehydration.