The carbon isotope compositions (δ13C values) of 23 hard ciders obtainable in the United States were analyzed to detect adjuncts, specifically added C4sugars (i.e., corn syrup and cane sugar). In contrast, the main ingredient of hard ciders is fruit, mostly apple, juice which is derived from C3plants. The labeled ingredients of ciders were found to be inconsistent with the carbon isotope ratios. A higher proportion of imported ciders studied had no isotopic evidence of added C4-based sweetener, while most domestic ciders had elevated δ13C values, indicative of C4-based sugar additives. European ciders could contain beet sugar, a common sweetener used in that region, which would not be detected as an additive because it is a C3-based sweetener. The δ13C values of the ciders were found to have no correlation with the amount of sugar in the cider, as reported on the nutritional information label, likely reflecting varying fermentation times. An increase in the amount of added C4sugars did not correspond to a decrease in price, in contrast to what is found in beers.