BACKGROUND: 'Reducing the Strength' (RtS) is a public health initiative encouraging retailers to voluntarily stop selling cheap, strong beers/ciders (≥6.5% alcohol by volume). This study evaluates the impact of RtS initiatives on alcohol availability and purchasing in three English counties with a combined population of 3.62 million people. METHODS: We used a multiple baseline time-series design to examine retail data over 29 months from a supermarket chain that experienced a two-wave, area-based role out of RtS: initially 54 stores (W1), then another 77 stores (W2). We measured impacts on units of alcohol sold (primary outcome: beers/ciders; secondary outcome: all alcoholic products), economic impacts on alcohol sales and substitution effects. RESULTS: We observed a non-significant W1 increase (+3.7%, 95% CI: -11.2, 21.0) and W2 decrease (-6.8%, 95% CI: -20.5, 9.4) in the primary outcome. We observed a significant W2 decrease in units sold across all alcohol products (-10.5%, 95% CI: -19.2, -0.9). The direction of effect between waves was inconsistent for all outcomes, including alcohol sales, with no evidence of substitution effects. CONCLUSIONS: In the UK, voluntary RtS initiatives appear to have little or no impact on reducing alcohol availability and purchase from the broader population of supermarket customers.