The origins of Kwil have never been made public. Although it is primarily a mood stabiliser, it is highly idiosyncratic in its reponses – although in large enough quantities it is a sedative, that size of that quantity varies wildly and unpredictably from person to person.
Unusually, for an hallucinogen, it does not cause hallucinations while the drug is in effect, but instead as a symptom of the hangover after it wears off. And like the sedative effects, the hallucinogenic effects are also wildly variable.
Fortunately, the effects do not vary from dose to dose – once a particular person has sampled the drug, they can have a fairly reliable idea of what its effects will be for them henceforth.