Greatmother Geyah wants you to speak with Mother Kashur.
Do not be alarmed by what you might see once the effect has taken hold! These spirits are all around us - always. The potion allows your mind to be able to understand and ultimately see the spirits. You will need to be under its influence if you are to speak with Mother Kashur.
You will find her a great ways to the southwest, at the Ancestral Grounds.