Or is that just an idea from Ubisoft?
you may be interested in a few earlier posts
Did professional assassins exist in medieval Europe? If so, where would they be trained? How would one become an assassin?
Is there any historical basis for hashish-consuming assassins in the Arab world?
a big thread from last week Two-parter: Is the word assassin actually derived from the word hashish? Did Hassan-i Sabbāh himself encourage his operatives (ie 'assassins') to use hashish?