Abstract: Provided herein are methods to determine the safety of quercetin compositions regarding contaminants that can result from the degradation of quercetin, such as by storage of solid form quercetin compositions in an air atmosphere. The contaminants include protocatechuic acid, 2,4,6-trihydroxybenzoic acid, and 2-(3,4-dihydroxybenzoyloxy)-4,6-dihydroxybenzoic acid. Provided herein are also methods which reduce degradation of solid form quercetin compositions and reduce the formation of such toxic compounds. The provided methods increase the shelf life and patient safety of quercetin compositions.