Okay kiddo, so imagine you have a boo-boo and your mommy gives you medicine to make it better. That medicine is called a pharmakon, which means it can be both helpful and harmful at the same time.
In philosophy, the word pharmakon is used to talk about things that have two opposite effects. Like how medicine can make you better, but if you take too much it can make you sicker. Or how sometimes something that is helpful for one person can be harmful for another.
It's kind of like a magic potion - you never know for sure what will happen when you drink it. It can be powerful and unpredictable, and that's what makes it so interesting to talk about in philosophy.