I would have read this around 1985-1998 because I remember being in school at the time. It may have been in a short story collection with "The Ugly Little Boy" and a story about a family dealing with people in the future coming back to enhance the intelligence of their baby with enfante terrible results. A boy, grade school age or so and very intelligent, discovers (or possibly just decides) that there are drugs in the food that prevent one from thinking critically. The details are kind of fuzzy in my head, but I remember that he at one point distills the chemical from his cereal, which he'd detected as having a high concentration, and overdoses. He's convinced that the government is trying to silence him — a scene that sticks out in my mind was him falling on a moving sidewalk and tearing his clothing as he tries to escape two "men in black" type figures that are pursuing him. The short story ended with him deciding that he was better off just consuming the food and being happy in his ignorance.
Years later, as an adult learning about mental illness, it struck me that the story was slightly ambiguous as to whether there actually were chemicals, and that the use of drugs that dulled his creativity and intelligence, and the decision to take them anyhow, was reminiscent of the feelings that manic people have toward their medications.
Anyone know what this one was?