Moste Potente Potions contained recipes for many dangerous, controversial, and arcane potions, which required advanced skill in potion-making to brew. Gruesome illustrations showed the effects of such potions. The Hogwarts Library accordingly kept its copy of this book in the Restricted Section.
Two potions known to be included in the book were Polyjuice Potion and Laxative Potion. It may have also contained information on slow-acting venoms, but this is uncertain.
Hermione obtained a permission slip to check Moste Potente Potions out of the Restricted Section from Gilderoy Lockhart, claiming that the book contained information on slow-acting venoms that she thought might help her understand what Lockhart had written on this subject in Gadding with Ghouls.
Also in the book, there is a picture (Figure VII) of a woman with a grotesquely large spider on her head, almost worn like an ornament. Whether or not this is an effect of a potion is unknown. It is possible that it is the side-effect of accidentally imbibing a Polyjuice Potion contaminated by spider hairs, similar as to when Hermione was partially transfigured into a cat when her Polyjuice Potion was contaminated with cat hair.
