Give orally daily or as directed by your veterinarian. Yeast Guard contains a small amount of goldenseal root powder. California placed goldenseal root powder on its Proposition 65 list in 2015, so we provide the warning as a conservative compliance measure. The warning does not mean Yeast Guard has been found to cause cancer or that it is unsafe for dogs when used as directed. California’s listing was based on a two year laboratory study in rats and mice. The animals were fed diets containing goldenseal root powder every day for essentially their entire lives. At the highest exposure, goldenseal made up 2.5% of everything they ate. That translated to daily doses as high as approximately: - 1,175 to 1,340 mg per kilogram of body weight in rats - 2,875 to 3,275 mg per kilogram of body weight in mice Those amounts bear little resemblance to the small, measured quantity of goldenseal contained in a serving of Yeast Guard. The results were also not uniform. Liver tumors increased in rats at the highest concentration and in male mice, while the study found no evidence of carcinogenic activity in female mice. Goldenseal root powder and its major constituent, berberine, were also negative in the genetic toxicity tests reported with the study. There is inadequate evidence that goldenseal causes cancer in humans. Nevertheless, California’s unusually broad warning law permits an ingredient to be listed based on animal studies involving exposure levels and conditions that may be dramatically different from normal product use. Proposition 65 is concerned with human exposure, even though Yeast Guard is formulated for dogs. The amount of goldenseal a person could encounter while measuring a normal serving is extremely small. However, California has not provided a simple safe harbor level for goldenseal root powder, and establishing that a warning is unnecessary can require costly product-specific exposure testing and legal analysis. We use goldenseal as one carefully measured component of Yeast Guard’s herbal formula. The Proposition 65 warning is a conservative legal disclosure—not evidence that the small amount in Yeast Guard presents a meaningful cancer risk during normal use.