apothecaries‘ weight

an obsolescent system of weights based upon the weight of a grain of wheat. Has been used for centuries in weighing medicines and precious metals (Troy measure). Some drugs which have been available for long periods are still often designated as grains (e.g., 5 grains of aspirin, 1/2 grain of codeine, 1/100 grain nitroglycerin). This weight system has been largely superseded by the metric system (based on grams). One grain is the equivalent of 64.8 milligrams. One scruple contains 20 grains; one dram contains 60 grains; one apothecary ounce contains 8 drams (480 grains); one apothecary pound contains 12 ounces (5760 grains).