Is that 800ug per kg? 800ug = 0.8 mg. In my case, that would be 61 mg. A quick look at supplements on Amazon shows that most capsules contain 750 to 1,100 mg each.
That probably refers to the amount of whole herb, not the active ingredient.
Link below refers to “Blessed Thistle (Cnicus benedictus) (aerial parts) 400 mg”. I get my supplemnts from Swanson but am not taking this one...
https://www.swansonvitamins.com/p/swanson-premium-full-spectrum-blessed-thistle-400-mg-90-caps