Stuff that allows it to form a solid block instead of powder. Stuff to time how long it takes to dissolve (how else can there be fast-acting and slow-acting versions?) Stuff to make the pills large enough to see with your eyes. A grain of sand is about 20 milligrams. Low-dose aspirin is 80 milligrams, but the pill is a much more convenient size than 4 grains of sand. (or 8 grains of sand, since sand is about twice as dense as pure ASA)