European Union law prohibits companies from marketing drugs off-label. In the United Kingdom—as in some other European countries, but unlike the United States—industry self-regulatory bodies are tasked with supervising compliance with marketing rules. The objectives of this study were to (1) characterize off-label promotion rulings in the UK compared to the whistleblower-initiated cases in the US and (2) shed light on the UK self-regulatory mechanism for detecting, deterring, and sanctioning off-label promotion.