Alchemist - skill building (questions, etc.) (The Witcher 3: Wild Hunt)

Here we discuss all the skills of alchemy.
Who did not follow the path of a warrior or magician, but an alchemist - explain how the "Contempt for Pain" skill works in the second row. It seems to depend on intoxication, and should increase maximum hp - but it does not visually increase. Explain who knows - how it works and whether it works at all?