To evaluate the effect of a sugar-sweetened beverage (SSB) tax implemented in Oakland, California, in July 2017, on prices of beverages sold in fast-food restaurants 2-year post-tax.

Using a difference-in-differences (DID) approach, we analysed beverage price data collected from fast-food restaurants 1-month pre-tax and 2-year post-tax in Oakland (intervention site) and Sacramento, California (comparison site). Separate linear regression models were used to estimate the impact of the tax on prices of bottled regular soda, bottled diet soda, bottled unsweetened beverages and fountain drinks.

Oakland and Sacramento, California, USA.

Chain and non-chain fast-food restaurants (n 85).

DID estimates indicate that in fast-food restaurants, on average, the price of bottled regular soda increased by 1·44 cents/oz (95 % CI 0·50, 2·73) (tax pass-through rate of 144 %) and the price of bottled diet soda increased by 1·17 cents/oz (95 % CI 0·07, 2·13). No statistically significant differences were found between bottled regular and diet soda price increases. Price effects for unsweetened beverages and fountain drinks were not statistically significant. Further, the estimated price change for fountain drinks was nearly zero.

Findings suggest that the effectiveness of SSB taxes in discouraging SSB consumption may be limited in fast-food restaurants in Oakland, California, because there were similar price increases in taxed and untaxed bottled soda and no changes in fountain drink prices.