Objective: The purpose of this study was to examine the efficacy of sending cards designed to prevent alcohol-related problems during 21st birthday celebrations. Method: College students were randomly assigned to receive cards with one of the following messages: (1) a neutral birthday greeting; (2) harm reduction information; (3) messages designed by the Be Responsible About Drinking (B.R.A.D.) Foundation, including harm reduction information and a description of the tragic death of Brad McCue during his 21st birthday celebration; (4) social norming messages designed to correct misperceptions of drinking; or (5) the combination of messages from Cards 2 and 4. A total of 994 students completed a post-21st birthday phone survey. Effects were evaluated in two cohorts with 444 and 550 students, respectively. Results: There were no significant effects of the cards on drinking or alcohol-related problems. Conclusions: These null findings, plus some unexpected trends in our data, highlight the importance of carefully evaluating mailed interventions before deploying them on a large scale.