Manuscript page: Petri's Philter is an alchemy formula in The Witcher 3: Wild Hunt that is needed to craft Petri's Philter.
It's a possible spawn at a random diagram location starting at level 2, or purchased from the following merchants:
- Otto Bamber at the Herbalist's Hut northeast of Oxenfurt
- Yolar at Gedyneith
- All herbalists in Toussaint except Pinastri
