A potion is a magical mixture that combines magical and mundane ingredients. Potions are brewed over a fire or thermal source, in a cauldron. The effects range from relieving headaches to increasing energy, causing a part of the body to swell, changing the color or appearance of the eyes, and even providing strong psychological effects or poisoning. The difficulty is also varied.

It is important to note that only a witch or wizard should ingest or apply a potion, regardless of the circumstances. Potions cause unusual reactions in Muggles. Before the International Statute of Magical Secrecy of 1689, certain magical and non-magical communities lived in close proximity, and in some cases magical people even held places of great esteem. Currently, the effect of potions on Muggles can be deadly.

A mundane example would be lactose intolerance, or raw milk. By having long exposure, your body digests it without problems, but if you are exposed to its absence for a long time, you will stop synthesizing the enzymes that digest that protein, making its consumption impossible. That's what happened to muggles with magic, and they can't stomach direct contact with it.