"In fact, it appears to have many of the same properties as veritaserum," The potion master continued "An adder’s tongue is often added to potions to counteract evil, wrongdoings, that sort of thing, but combined with jellyfish venom, which appears to have occurred, it would have taken the opposite effect. From what I can gather, the poison befuddles the mind, causing the user to act on their deepest subconscious and increasing susceptibility to possibly dangerous levels. The poison, unchecked, would eventually turn the mind to such  mush  that the brain would, in every sense of the word,  forget  to function. That was indeed a  very handy antidote." 