Background <p>Colorectal cancer (CRC) is a leading cause of cancer-related morbidity and mortality in the United States (U.S.). CRC screening (CRCS) is an important method of cancer prevention and early detection, but often receives less public attention than other cancer and screening types. Regular CRCS is recommended for most individuals aged 45–75, though screening rates are lower than desired in the U.S. Despite similar screening rates, Black Americans experience a variety of CRC-related disparities including higher incidence and mortality rates in the United States. Research suggests Black Americans often do not receive timely follow ups to stool-based screening tests and receive lower quality endoscopic care. Effective public health communication strategies are needed to improve CRCS rates, particularly among populations experiencing disparities. The current study tests the ability of a novel approach to content generation and selection (crowdsourcing) to identify effective public health communication content.</p> Methods/design <p>This protocol is for a five-arm, online, randomized controlled trial testing different CRCS content types among white and Black/African Americans. In total, 2,000 non-Hispanic Black (<i>n</i> = 1,000) and white (<i>n</i> = 1,000) Americans will be recruited into the trial, randomized into one of five conditions. The five conditions are based on content rankings and preferences from our previous work: (1) overall preferred content, (2) Black American preferred content, (3) white American preferred content, (4) median ranked content (i.e., “standard of care”), and (5) control/no exposure to content. The primary outcomes are intentions to adhere to CRCS recommendations and screening preferences for intentions to adhere. Secondary outcomes include likelihood of sharing information via social media and information sharing behavior. Comparisons will be examined for differences in outcomes as hypothesized, with exploratory analyses undertaken as well. The study is powered to detect a small effect, which is expected based on past research.</p> Discussion <p>The trial aims to determine the effectiveness of crowdsource-selected CRCS messages to improve screening intentions and likelihood of sharing information via social media. This trial takes an important step in testing an innovative and scalable approach to identify and select content to be disseminated by public health communicators.</p> Trial registration <p>NCT06712901.</p>