They are round units, in a dinosaur apothecary system. 325mg is 5 "grains". "A grain is a unit of measurement of mass, and in the troy weight, avoirdupois, an

They are round units, in a dinosaur apothecary system. 325mg is 5 "grains". "A grain is a unit of measurement of mass, and in the troy weight, avoirdupois, and apothecaries' systems, equal to exactly 64.79891 milligrams" https://en.wikipedia.org/wiki/Grain_(unit) https://en.wikipedia.org/wiki/Grain_(unit) 81mg = 1.25 grains. What ends up happening is a big study is done on an existing formulation of an old drug, results look good, and then you have to ask yourself: do you mess around with the dosing to get a round number, or go with what's been proven?