Diketopirerazine (DKP) is a by-product of aspartame metabolism. DKP is formed in liquid aspartame-containing products during prolonged storage. It has been implicated in the occurrence of brain tumors and has also been implicated as a cause of uterine polyps and changes in blood cholesterol by FDA toxicologist Dr. Jacqueline Verret in her testimony before the U.S. Senate.