I went up to 4 and even 6 Swanson DHQ capsules per day, and started to feel strong mental overstimulation, probably caused by the fact that DHQ is closely related to quercetin, and in the past I also observed quercetin to overstimulate. But I found 2 capsules of DHQ per day were fine. Though I have not done any long term tests of DHQ as yet, just brief tests.
The oral absorption of DHQ is only 0.49% according to
this study (in which DHQ is called by its other name taxifolin).
However,
this study says that
oral DHQ absorption goes up to 36% if dissolved in lipid solution. So it might be a good idea to swallow a tablespoon or two of cooking oil or coconut oil with your DHQ.
But for me, the oral bioavailability of DHQ is not the issue, in that I can't really go higher than 2 capsules a day anyway, because of the overstimulation side effect. So that is already the maximum dose I can comfortably handle. I took my DHQ with some coconut oil, so maybe I was getting pretty good bioavailability.