A Shrinking Solution, or a Shrinking Potion, is a potion in Harry Potter and the Prisoner of Azkaban. It presumably shrinks whoever or whatever drinks it. Ingredients include shredded Daisy root, skinned Shrivelfig, chopped up caterpillars, a rat spleen and a dash of leech juice.[1]
If done accurately, it can shrink a toad back into a tadpole. An unknown antidote will reverse the effect. If it is produced wrong, it might be poisonous to whoever or whatever drinks it.[1]
Students at Hogwarts School of Witchcraft and Wizardry study the Shrinking Solution in Potions. In the summer leading up to their third-year, Harry Potter's year had to do homework about the potion. He found it difficult.[2] In September, they had to create the potion. Neville Longbottom did a couple of ingredients wrong, causing the solution to turn orange instead of acid green. Professor Snape told Neville he would feed it to Trevor, but Hermione Granger improved it before he could and the toad was fine.[1]