Yup, boric acid (aka 20 Mule Team Borax) is used as roach poison, but also as a cleaner/disinfectant. You simply don't eat it, dear boy. There's a lot of stuff with multiple uses. My mom used hydrogen peroxide as a disinfectant...I freaked when I learned that people put it on their hair to change the colour.... ;D Epsom Salts is also a disinfectant for cuts etc as a soak, and a hella laxative if you drink it...and here they use it on the streets to get the candle wax off the pavement after Easter processions, which in this city are legion.
Alum is used in cooking in the States and is impossible to find here except in 2-kilo sacks at pharmacies (with a special certificate stating what you want it for) or at farmer's supply stores because it's used on grapevines. But a small box of alum for cooking purposes you cannot get. Nobody makes their own candy here.

Chemistry is cool like that.