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)

Excedrin brand in the US has tablets with caffeine and aspirin, for example, but people might just call them aspirin (my grandmother, for example).