General Mills introduced two new cereals in 1971, Count Chocula and Franken Berry. Like Lucky Charms, they were cereals studded with colored marshmallows, super-sweetened to appeal to children. Both cereals were an immediate hit, and even today show up in grocery aisles around Halloween. Some kids noticed a side effect of eating Franken Berry right away, that it made your poop bright pink. Parents were shocked, and some took their children to a doctor or even an emergency room to check for internal bleeding. The condition soon earned its own name: "Franken Berry Stool." Read about the panic and what the cereal maker did about it at Atlas Obscura.
(Image credit: Flickr user GeneralMills)
They changed the cereal recipe, so at the very least Count Chocula and Booberry aren't the same as they were years ago (for better or worse).
Abusive comment hidden.
(Show it anyway.)
I remember in Stephen King's "Cujo" how a version of this was integrated... only a bit more "gruesome". One morning a kid started vomiting blood after eating cereal. The mom panics and goes to the hospital, only to find it was just regular vomit, but the red food coloring in the cereal made it seem like it was blood. They changed to formulation and all was well, but the nationwide panic and blood-vomiting kids meant the cereal never recovered its popularity. (Loosely remembered from 30 years ago)
Abusive comment hidden.
(Show it anyway.)