You swallow a dose of poison with no effect and regurgitate a dose of a different poison (your choice) into the old container (or another you have on hand). Attempt a Craft (alchemy) check against the new poison’s DC. If you succeed, you create a dose of your chosen poison. If you fail, the poison you regurgitate is inert. If you roll a natural 1, you expose yourself to the original poison (although you remain immune to that poison if you have venom immunity or a similar class feature or ability). The new poison’s price must be the same as or less than the original poison’s price.
Pathfinder Campaign Setting: Inner Sea Intrigue © 2016, Paizo Inc.; Authors: David N. Ross, with Ross Byers.