This report presents data from the 2015 National Survey on Drug Use and Health (NSDUH) regarding the perceived harmfulness of using cigarettes,alcohol, and specific illicit drugs and the perceived availability of substances. Estimates are presented for specific age groups. Estimates of the perceived great risk of harm associated with the use of marijuana, cocaine, alcohol, and cigarettes also are presented according to whether people initiated use of these substances in the past year. In addition, the report presents estimates for youth-specific protective factors, such as perceptions about parents strongly disapproving of youth substance use. Finally, this report presents the estimated numbers of individuals who initiated substance use in the past year and the average age at first use among people who initiated use in the past year (i.e., past year initiates). Statistically significant differences are noted for these various estimates.