Any added poisonous or deleterious substance, or any color additive, shall with respect to any particular use or intended use be deemed unsafe with respect to any drug, device, or cosmetic, unless there is a regulation allowing limited use of a quantity of such substance, and the use or intended use of such substance conforms to the terms prescribed by regulation. While such regulations relating to such substance are in effect, a drug or cosmetic shall not, by reason of bearing or containing such substance in accordance with the regulations, be considered adulterated.