Pyroglutamic acid (5-oxoproline) is a cyclized derivative of L-glutamic acid. It is an uncommon amino acid derivative in which the free amino group of glutamic acid cyclizes to form a lactam. It is formed nonenzymatically from glutamate, glutamine, and gamma-glutamylated peptides, but it can also be produced by the action of gamma-glutamylcyclotransferase on an L-amino acid. Elevated blood levels may be associated with problems of glutamine or glutathione metabolism. This compound is found in substantial amounts in brain tissue and other tissues in bound form, especially skin. It is also present in plant tissues. It is sold, over the counter, as a "smart drug" for improving blood circulation in the brain. Pyroglutamate in the urine is a biomarker for the consumption of cheese. When present in sufficiently high levels, pyroglutamic acid can act as an acidogen and a metabotoxin. An acidogen is an acidic compound that induces acidosis, which has multiple adverse effects on many organ systems. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of pyroglutamic acid are associated with at least five inborn errors of metabolism including 5-oxoprolinuria, 5-oxoprolinase deficiency, glutathione synthetase deficiency, hawkinsinuria, and propionic acidemia. Pyroglutamic acid is an organic acid. Abnormally high levels of organic acids in the blood (organic acidemia), urine (organic aciduria), the brain, and other tissues lead to general metabolic acidosis. Acidosis typically occurs when arterial pH falls below 7.35. In infants with acidosis, the initial symptoms include poor feeding, vomiting, loss of appetite, weak muscle tone (hypotonia), and lack of energy (lethargy). These can progress to heart, liver, and kidney abnormalities, seizures, coma, and possibly death. These are also the characteristic symptoms of the untreated IEMs mentioned above. Many affected children with organic acidemias experience intellectual disability or delayed development. In adults, acidosis or acidemia is characterized by headaches, confusion, feeling tired, tremors, sleepiness, and seizures. It has been shown that pyroglutamic acid releases GABA from the cerebral cortex and displays anti-anxiety effects in a simple approach-avoidance conflict situation in the rat. In clinical pharmacology experiments, pyroglutamic acid significantly shortens the plasma half-life of ethanol during acute intoxication.