identifying effective summary formats is fundamental to multiple fields including science communication, systematic reviews, evidence-based policy and medical decision-making. This study tested whether table or text-only formats lead to better comprehension of the potential harms and benefits of different options, here in a medical context. pre-registered, longitudinal experiment: between-subjects factorial 2 (message format) × 2 topic (therapeutic or preventative intervention) on comprehension and later recall (CONSORT-SPI 2018). longitudinal online survey experiment. 2305 census-matched UK residents recruited through the survey panel firm YouGov. comprehension of harms and benefits and knowledge recall after six weeks. fact boxes-simple tabular messages-led to more comprehension (d = 0.39) and slightly more knowledge recall after six weeks (d = 0.12) compared to the same information in text. These patterns of results were consistent between the two medical topics and across all levels of objective numeracy and education. Fact boxes were rated as more engaging than text, and there were no differences between formats in treatment decisions, feeling informed or trust. the brief table format of the fact box improved the comprehension of harms and benefits relative to the text-only control. Effective communication supports informed consent and decision-making and brings ethical and practical advantages. Fact boxes and other summary formats may be effective in a wide range of communication contexts.