But inversely, unless you actually go above 10, eg 15... The blood saturation isn't enough for your brain to take advantage of it.
But there is very little studied about sustained use of such a dosage. (Only short term - eg 1 week - which isn't long enough for the benefits again)
It's safe enough for anecdotes of people doing it for years and not having issues - but despite others claiming that it's well studied, it's really not - at least not with dosages above 5g in humans.
Personally I've been doing so for a year now and can unquestionably confirm a strong effect, which goes away if I reduce the dosage below the threshold. So at least my body responds to it.
But you're not getting a proper study unless you get thousands of people to take it for years... Which is basically impossible as there are too many confounding factors to get meaningful results.
And organizing such a study is gonna be too expensive too, with no sponsors willing to take up the tab
I've already written and edited this comment a lot, but as a final remark I'd like to point out that the benefits I'm referencing is having an easier time concentrating. This can also be a demerit, as you can easily be caught thinking about something for pretty long before you realize.