Doctor's best nattokinase (2000fu) 540vc contains 2,000 fibrinolytic units, which refers to the enzyme activity level. Enzymes, like nattokinase, are not measured in mg, but in an unassociated measure of units. Even if the enzyme had 1,000mg per capsule but no activity, the enzyme would be worthless. Doctor's best nattokinase has 2,000fu (units) of activity. This is a very high amount of activity.