This report presents data from the 2002 through 2014 National Surveys on Drug Use and Health (NSDUHs) for trends in people’s perceptions of great risk of harm associated with the use of cigarettes, alcohol, and specific illicit drugs and the perceived availability of substances. The data are presented for the population aged 12 years old or older and for specific age groups. Trends in perceived great risk of harm associated with the use of specific substances (i.e., marijuana, alcohol, and cigarettes) were compared with trends in the use of these substances in the past 30 days. The report also includes trends for measures that are specific to youths aged 12 to 17, such as perceptions about parents strongly disapproving of youth substance use. Finally, this report includes trends in 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). The report focuses on long-term trends by comparing estimates from the 2014 NSDUH with NSDUH estimates in 2002 to 2013. Statistically significant differences are noted between estimates in 2014 and those in prior years.