Background and aims The UK low‐risk drinking guidelines (LRDG) recommend not regularly drinking more than 14 units of alcohol per week. We tested the effect of different pictorial representations of alcohol content, some with a health warning, on knowledge of the LRDG and understanding of how many drinks it equates to. Design Parallel randomized controlled trial. Setting On‐line, 25 January–1 February 2019. Participants Participants (n = 7516) were English, aged over 18 years and drink alcohol. Interventions The control group saw existing industry‐standard labels; six intervention groups saw designs based on: food labels (serving or serving and container), pictographs (servings or containers), pie charts (servings) or risk gradients. A total of 500 participants (~70 per condition) saw a health warning under the design. Measurements Primary outcomes: (i) knowledge: proportion who answered that the LRDG is 14 units; and (ii) understanding: how many servings/containers of beverages one can drink before reaching 14 units (10 questions, average distance from correct answer). Findings In the control group, 21.5% knew the LRDG; proportions were higher in intervention groups (all P < 0.001). The three best‐performing designs had the LRDG in a separate statement, beneath the pictograph container: 51.1% [adjusted odds ratio (aOR) = 3.74, 95% confidence interval (CI) = 3.08–4.54], pictograph serving 48.8% (aOR = 4.11, 95% CI = 3.39–4.99) and pie‐chart serving, 47.5% (aOR = 3.57, 95% CI = 2.93–4.34). Participants underestimated how many servings they could drink: control mean = −4.64, standard deviation (SD) = 3.43; intervention groups were more accurate (all P < 0.001), best performing was pictograph serving (mean = −0.93, SD = 3.43). Participants overestimated how many containers they could drink: control mean = 0.09, SD = 1.02; intervention groups overestimated even more (all P < 0.007), worst‐performing was food label serving (mean = 1.10, SD = 1.27). Participants judged the alcohol content of beers more accurately than wine or spirits. The inclusion of a health warning had no statistically significant effect on any measure. Conclusions Labels with enhanced pictorial representations of alcohol content improved knowledge and understanding of the UK's low‐risk drinking guidelines compared with industry‐standard labels; health warnings did not improve knowledge or understanding of low‐risk drinking guidelines. Designs that improved knowledge most had the low‐risk drinking guidelines in a separate statement located beneath the graphics.

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Aim The Chief Medical Officer of England writes an annual social-norms-feedback letter to the highest antibiotic-prescribing GP practices. We investigated whether sending a social-norms-feedback letter to practices whose prescribing was increasing would reduce prescribing. Subject and methods We conducted a two-armed randomised controlled trial amongst practices whose STAR-PU-adjusted prescribing was in the 20th–95th percentiles and had increased by > 4% year-on-year in the 2 previous financial years. Intervention practices received a letter on 1st March 2018 stating ‘The great majority (80%) of practices in England reduced or stabilised their antibiotic prescribing rates in 2016/17. However, your practice is in the minority that have increased their prescribing by more than 4%.’. Control practices received no letter. The primary outcome was the STAR-PU-adjusted rate of antibiotic prescribing in the months from March to September 2018. Results We randomly assigned 930 practices; ten closed or merged pre-trial, leaving 920 practices — 448 in the intervention and 472 in the control. An autoregressive and moving average model of first order ARMA(1,1) correlation structure showed no effect of the intervention (β < −0.01, z = −0.50, p = 0.565). Prescribing reduced over time in both arms (β < −0.01, z = −36.36, p < 0.001). Conclusions A social-norms-feedback letter to practices whose prescribing was increasing did not decrease prescribing compared to no letter. Trial registration NCT03582072.