I'd say getting dermopathy is acquired by heavy usage...however, some people report deromopathy after short periods of use and others get away with heavy consumption without much dermopathy to speak of.
There should also be a distinction between Henry's example of a
single experience being heavy and your
overall kava drinking being heavy.
In the case of kava, I don't consider 'heavy' drinking to be synonymous with problematic or dangerous. If that's what we're aiming for, then maybe I'd say
frequent consumption of amounts that create double vision and world spinning might be problematic...but even then, you wouldn't likely show any negative impact on your health aside from dermo and most likely sluggishness, both of which are harmless and clear up upon cessation.
Also, there's no way to determine an official dose that is
the line where it becomes 'too much' or will be a definite cause of dermo. Overall KL% can easily range from 4% to 14%...which will make your standard dose different depending on what you have, using a fine strainer drastically reduces how many kavalactones you ingest and also seems to aid in keeping dermo away longer. A different persons body chemistry may be more prone to dermopathy than another person, and one persons 'mega-dose' might feel like another's average dose.
When you see me talk about drinking 8-12 Tbsp of kava, it doesn't mean I'm several times more affected by it, it's just where my body begins to feel the full effects that many others say they feel at the 3-4 Tbsp level. In fact, it appears that a lot of you can get way more jacked than me, on much less. My 8 is your 4.
When I saw a campaign in Vanuatu trying to reduce over consumption, the poster showed six shells as being too much...I'm not sure what it was based off of, or if it was just an arbitrary amount created by the government or some christian group or something...but in Vanuatu shells can be big and shells can be strong. I've tried to compare my dry powder dosages to what the equivalent would be in Vanuatu nakamals, it's at least within my range of 8-12 Tbsp worth of kavalactones over the course of a few shells...just not as dirty feeling and overall more pleasant and ideal. It can't perfectly be equated, but the closest I can convey would actually be like using a huge amount, maybe 16-20 Tbsp, but running it through a super fine strainer.
Two shells in Vanuatu usually set me up good, quickly. 3 gets me startin' to feel swashy.
(sorry I can't define that word). Vanuatu shells get me to a pleasant and notable kava-plane much easier and quicker than almost anything I can muster up at home, most of the time. I'd venture to say there's more or perhaps the same amount of kavalactones in 2 good, big Vanuatu shells, as there is in your entire homemade batch ... if you're a 3-5 Tbsp type of drinker. These guys are drinkin' that strength daily, maybe only a couple shells some nights, and 6 shells another night...and there's plenty of 1.5 liter plastics being filled up to take away...they seem to be gettin' along just fine and happy as ever.
So in general, since there is no real health threat involved with kava, I think it's up for the person to decide where
their personal heavy-usage line is at..after they've experienced kavas common side-effects. If you've never experienced any negatives, then you haven't even come close to heavy consumption.