Taken from "hands of the healer"
in short : ease mental travail (gm discretion), cures many diseases (gm discretion), neutralizes minor poisons, slows major poisons, staves off supernatural maladies and hastens the effect of wounds (x3).
Potency increased in the hands of a royal scion of luthien's line (no brother to the king, no cousin, just someone who his king, who will be king or should be king : in clear all the firstborn in right who can claim luthien as an ancestor). I interpret this as : faster relief and can cure major poisons. but i think it really means "gm's discretion".
It is not rare, can be found among the many weeds and flowers of any numenorean settlement, can be used directly without any preparation and still is noted as costing 180 to 300 gp. Seriously, 300 gp for a savage weed that grows along the roads is pure madness. I guess it is the price someone living reallly far from the west would pay. But what would be the point of paying 300 gp for this when you can find it on the borders of your village ?