Sober Truth on Preventing Underage Drinking Act or the STOP Act - Amends the Public Health Service Act to revise and expand the program to reduce underage drinking by: (1) expressing the sense of Congress that the National Minimum Drinking Age Law has been an effective public health and safety policy and has reduced drinking and driving traffic fatalities; (2) expanding the national media campaign to prevent underage drinking; (3) authorizing the Administrator of the Substance Abuse and Mental Health Services Administration, in coordination with the Director of the Office of National Drug Control Policy, to make supplemental grants to eligible entities to enhance collaboration between communities and institutions of higher education to prevent and reduce underage alcohol use; (4) requiring the Administrator to make grants to professional pediatric provider organizations to increase effective practices, including the screening of children and adolescents for alcohol use, to reduce the prevalence of alcohol use among individuals under the age of 21, including college students; (5) expanding data collection and research activites with respect to underage drinking; and (6) requiring the National Academy of Sciences to conduct a review of the research on the influence of drinking alcohol on adolescent brain development and the public policy implications of such research.