Hypoglycemia (also spelled hypoglycaemia or hypoglycæmia, not to be confused with hyperglycemia) is a medical emergency that involves an abnormally diminished content of glucose in the blood. The term literally means “low blood sugar” (Gr. ὑπογλυκαιμία, from hypo-, glykys, haima). It can produce a variety of symptoms and effects but the principal problems arise from an inadequate supply of glucose to the brain, resulting in impairment of function (neuroglycopenia). Effects can range from mild dysphoria to more serious issues such as seizures, unconsciousness, and (rarely) permanent brain damage or death. The most common forms of hypoglycemia occur as a complication of treatment of diabetes mellitus with insulin or oral medications. Hypoglycemia is less common in non-diabetic persons, but can occur at any age. Among the causes are excessive insulin produced in the body (hyperinsulinemia), inborn error of metabolism, medications and poisons, alcohol, hormone deficiencies, prolonged starvation, alterations of metabolism associated with infection, and organ failure. Hypoglycemia is treated by restoring the blood glucose level to normal by the ingestion or administration of dextrose or carbohydrate foods. It is often self-diagnosed and self-medicated orally by the ingestion of balanced meals. In more severe circumstances, it is treated by injection or infusion of glucagon. Recurrent hypoglycemia may be prevented by reversing or removing the underlying cause, by increasing the frequency of meals, with medications like diazoxide, octreotide, or glucocorticoids, or by surgical removal of much of the pancreas. The level of blood glucose low enough to define hypoglycemia may be different for different people, in different circumstances, and for different purposes, and occasionally has been a matter of controversy. Most healthy adults maintain fasting glucose levels above 4.0 mmol/L (72 mg/dl), and develop symptoms of hypoglycemia when the glucose falls below 4 mmol/L. It can sometimes be difficult to determine whether a person’s symptoms are due to hypoglycemia. Criteria referred to as Whipple’s triad are used to determine a diagnosis of hypoglycemia: Symptoms known to be caused by hypoglycemia Low glucose at the time the symptoms occur Reversal or improvement of symptoms or problems when the glucose is restored to normal Hypoglycemia (common usage) is also a term in popular culture and alternative medicine for a common condition characterized by shakiness and altered mood and thinking, but without measured low glucose or risk of severe harm. It is treated by changing eating patterns, i.e. eating regular balanced meals with reasonable portions and avoiding excessive sugar.