You have a book or collection of notes that you study to prepare your apothecary spells, develop your esoteric theories, and record your occult practices. You may use your formula book as an arcane focus for your apothecary spells. You may describe this book any way you like. Some examples of your book's appearance include:
- A large leather-bound tome with yellowing pages bound shut with an iron lock
- A scattered assortment of scribbled notes loosely held together by rope
- A pristine journal with perfect edges and beautiful penmanship
- A leather briefcase with two small golden locks
- A medical bag with surgical symbols on the sides
- A beat-up satchel slung over one shoulder with vials and bottles poking out of every pocket
If the book is destroyed or lost, you can recreate it using inks and paper during a long rest.