Kryptopyrroluria (KPU) and Hämopyrrolactamuria (HPU) are common but often overlooked metabolic disorders. A variety of conditions correlate with KPU or HPU, or can be a direct consequence, such as histamine intolerance, anxiety, depression, thyroid disorders (Hashimoto's thyroiditis), and chronic fatigue states with or without adrenal insufficiency. Dr. Carl Pfeiffer, the physician who discovered KPU, estimated that more than 10% of the population is affected by KPU. The authors have been treating people with KPU and HPU for years and believe that these should be seen as independent factors in many chronic diseases. From their own therapeutic experiences with hundreds of patients, they have developed a comprehensive diagnostic and therapeutic concept that enables effective treatment.