Alchemic concoction. Completely reduces stamina, exhausting the player.
Nigred is an item in Haunting Ground. It has negative effects, as it completely reduces stamina when consumed.
If the player is carrying Withered Flowers, it is possible to turn them into Nigred after placing them in a refining machine after Fiona is rescued from her cell in the Water Tower. This most likely proves that Nigred came from these flowers.