Final answer:
Products with aspartame must contain a warning label for people with PKU (phenylketonuria).
Step-by-step explanation:
Products with aspartame must contain a warning label for people with PKU (phenylketonuria). PKU is a recessive genetic disease where individuals lack the enzyme needed to break down phenylalanine, a component of aspartame. Phenylalanine levels rise to toxic levels in the body and can cause damage to the central nervous system and brain.