Chapter XV: Section 7: of this act states

"That for the purposes of this Act an article shall be deemed to
be adulterated: in case of drugs:

"_First._ If, when a drug is sold under or by a name recognized in
the United States Pharmacopoeia or National Formulary, it differs
from the standard of strength, quality, or purity, as determined
by the test laid down in the United States Pharmacopoeia or
National Formulary official at the time of investigation;
_Provided_, that no drug defined in the United States
Pharmacopoeia or National Formulary shall be deemed to be
adulterated under this provision if the standard of strength,
quality, or purity be plainly stated upon the bottle, box or other
container thereof although the standard may differ from that
determined by the test laid down in the United States
Pharmacopoeia or National Formulary.

"_Second._ If its strength or purity fall below the professed
standard or quality under which it is sold."