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BACKGROUND In 2020, San Francisco, CA, amended an ordinance requiring warning labels on advertisements for sugary drinks to update the warning message. No studies have evaluated consumer responses to the revised message. OBJECTIVES To evaluate responses to the 2020 San Francisco sugary drink warning label and to assess whether these responses differ by demographic characteristics. DESIGN Randomized experiment. PARTICIPANTS AND SETTING During 2020, a convenience sample of US parents of children aged 6 months to 5 years (N = 2,160 included in primary analyses) was recruited via an online panel to complete a survey. Oversampling was used to achieve a diverse sample (49% Hispanic/Latino[a], 34% non-Hispanic Black, and 9% non-Hispanic White). METHODS Participants were randomly assigned to view a control label ("Always read the Nutrition Facts Panel") or the 2020 San Francisco sugary drink warning label ("SAN FRANCISCO GOVERNMENT WARNING: Drinking beverages with added sugar(s) can cause weight gain, which increases the risk of obesity and type 2 diabetes."). Messages were shown in white text on black rectangular labels. MAIN OUTCOME MEASURES Participants rated the labels on thinking about health harms of sugary drink consumption (primary outcome) and perceived discouragement from wanting to consume sugary drinks. The survey was available in English and Spanish. STATISTICAL ANALYSES PERFORMED Ordinary least squares regression. RESULTS The San Francisco warning label elicited more thinking about health harms (Cohen's d = 0.24; P < 0.001) than the control label. The San Francisco warning label also led to more discouragement from wanting to consume sugary drinks than the control label (d = 0.31; P < 0.001). The warning label's influence on thinking about harms did not differ by any participant characteristics, including age, gender, race/ethnicity, education, income, or language of survey administration (all P values for interactions > 0.12). CONCLUSIONS San Francisco's 2020 sugary drink warning label may be a promising policy for informing consumers and encouraging healthier beverage choices across groups with diverse demographic characteristics.