Since I encountered hazia in MoB's Sun County, and of course the Earthsea book, I've taken it as more than just a drug.
Like so many things there, in my game hazia can is a tool & drug of the EWF mystics. The altered state that the drug produces can be used by shaman's to help with discorporation, or making spirits visible. For the EWF though, it was an aide to getting in touch with the inner dragon, and to activate the tele-empathy needed to understand dragonewt speech.
Since the EWF teachings have been forgotten, outside of the praxian spiritists the plant has become just a recriational drug that turns people's attentions away from their real lives (of course that's pretty much what the EWF was like anyway, with their disdain for the mundane world).
As for the effects, I use a mix / combination of cannabis and opium. To an advanced EWF mystic it's like a very mild strain of cannabis. When properly processed, it can be a powerful opiate that brins stupor and strange dreams.
-Adept
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