IMPORTANCE: The US Supreme Court decision Murphy v National Collegiate Athletic Association allowed states beyond Nevada to legalize sports betting, including online wagers. How sports betting has evolved and its association with gambling harms has not been studied. OBJECTIVE: To describe how US sports betting evolved after Murphy v National Collegiate Athletic Association and offer insights into the potential health effects of sportsbooks, which are platforms for wagering on sporting events. EXPOSURE: Enactment of (1) Murphy v National Collegiate Athletic Association nationally and (2) the opening of retail or online sportsbooks in states. DESIGN, SETTING, AND PARTICIPANTS: In this longitudinal study, aggregate US internet search trends for gambling addiction and wagers on sports were described before and after the emergence of legalized sportsbooks. MAIN OUTCOMES AND MEASURES: Internet searches per 10 million queries that mentioned gambling and addiction, addict, anonymous, or hotline (such as gambling addiction hotline) made to Google from January 1, 2016, through June 30, 2024. RESULTS: The number of states with operational sportsbooks increased from 1 during 2017 to 38 during 2024. Total sports wagers increased from .9 billion during 2017 to 21.1 billion during 2023, with 94% of wagers during 2023 being placed online. There were 23% (95% CI, 15%-30%) more searches nationally for gambling addiction help-seeking after Murphy v National Collegiate Athletic Association. Massachusetts (47%
95% CI, 21%-79%), New Jersey (34%
95% CI, 21%-45%), New York (37%
95% CI, 26%-50%), and Pennsylvania (50%
95% CI, 35%-66%) each had more searches than expected after the opening of any sportsbooks in their state. Additional analyses suggest the opening of online, vs retail, sportsbooks corresponded with a larger increase in searches. CONCLUSIONS AND RELEVANCE: The results of this time series study suggest that access to sportsbooks, sports wagers, and potential help-seeking for gambling addiction increased substantially and highlight the need to address the health implications of sportsbooks, including recognition and treatment of gambling problems and their broader societal implications.