The study concludes that the cost of substance abuse could be offset by a nationwide implementation of effective prevention policies and programs. This report summarizes existing estimates of the costs of substance abuse and its adverse consequences. These cost estimates are used to assess the benefits of prevention in existing cost-benefit analyses. The estimates reviewed highlight the total annual costs of substance abuse from a number of perspectives, including social costs and the direct costs to State government. Another section of this report analyzes the probable outcomes of implementing school-based substance abuse prevention programming nationwide in 2002 for youth ages 12-17. If effective school-based substance abuse prevention programs were implemented nationwide, substance abuse initiation would decline for 1.5 million youth and be delayed for 2 years on average. The average effective school-based program in 2002 cost $220 per pupil, including materials and teacher training. These programs could save an estimated $18 per $1.00 invested if implemented nationwide. Although 80 percent of American youth reported participation in school-based prevention programs in 2005, only 20 percent were exposed to effective prevention programs. Another section of the report summarizes existing costs and benefits of substance abuse and related prevention programs from society's perspective. It draws heavily on two systematic evaluations of cost-savings estimates, adds new analyses, and includes many programs listed on the Substance Abuse and Mental Health Services Administration's (SAMHSA's) National Registry of Evidence-based Programs and Practices. The report suggests how these cost-savings estimates might be used to create an integrated, comprehensive, and cost-effective approach to substance abuse prevention. 19 tables, 5 figures, 59 references, and appended descriptions of methods