Based on the above indication of conversion (established in 2012) we have the following comparisons. 5 grains of aspirin according to this system is approximately equivalent to a standard dose of 325mg, for instance.
Apothecaries’:
1 grain=64.8mg=0.0648g
1 scruple=1296mg or 1.296g
1 dram=3888mg or 3.888g
1 ounce=31104mg or 31.104g
1 pound=373248mg or 373.248g or 0.373248kg
The apothecary unit hasn’t been specified, but, since prescriptions usually contain low quantities of drugs, maybe we can assume the units are grains, in which case:
(a) 2 grains=129.6mg=0.13g approx
(b) 5½ grains=356.4mg=0.36g approx