One of the dangerous and life threatening side effects of SSRI is serotonin level in the brain. This happens when there is an interaction of SSRI with monoamine oxidase inhibitors (MAOIs). It can also occur if SSRI is taken with other medicine. The symptoms take effect so fast that it can trigger within minutes. It may include shivering, increased heart rate, sweating, myoclonus, dilated pupils and overresponsive reflexes. With moderate intake of SSRI, high blood pressure, hyperthermia and hyperactive bowel sound with a bodily temperature of 40 °C might show up. Hyperthermia can cause other abnormalities which include seizures, metabolic acidosis, rhabdomyolysis, disseminated intravascular coagulation and renal failure.

Overdosing of SSRI can lead to the cause of serotonin syndrome. The enzyme monoamine oxidase becomes irreversible after reacting with SSRI. As a result the body needs to produce more enzymes to overcome the serotonin syndrome which might take more than 4 weeks.

The serotonin syndrome can be very complex in an individual. The syndrome has been observed among all age groups includig newborn infants. Diagnosis of serotonin syndrome can be carried out by observing and investigating the patient’s history. The symptoms which are checked in a diagnosis include clonus, tremor and akathisia.