1. A drug shall be deemed to be adulterated if it is represented as a drug, the name of which is recognized in an official compendium, and its strength differs from, or its quality or purity falls below, the standard set forth in the compendium. The determination as to strength, quality or purity must be made in accordance with the tests or methods of assay set forth in the compendium or, in the absence of or inadequacy of those tests or methods of assay, those prescribed pursuant to the Federal Act.
2. A drug which is defined in an official compendium shall not be deemed to be adulterated under this section because it differs from the standard of strength, quality or purity set forth in the compendium if that difference is plainly stated on its label.