Sugar is not poison, it is a nutrient, it is a type of carbohydrate. However even nutrient can become poisonous at the right high dosage. Dosage makes the poison. Even water at the right dosage can cause coma and death. During emergency situations, glucose (a sugar) is used to quickly raise blood sugar levels. Too much sugar is bad for you but it is not a poison.

Poison are stuff that harms the body when absorbed at any dosage, they don’t provide any benefit and the body can’t use it to thrive, they are not nutrients, example plutonium. plutonium is toxic, a poison at any dosage.