Most diet sodas come with a disclaimer about phenylalanine, an ingredient found in artificial sweeteners. Although phenylalanine is something we actually can’t live without, too much of it can be dangerous. People with a genetic condition called PKU can’t break down phenylalanine after use, and ingesting too much can lead to a range of symptoms from inattention to seizures. That’s why the disclaimer on soda warns people with PKU not to accidentally overload their systems. To learn more, you can watch the full-length SciShow video about phenylalanine and more.