The 2010/11 BCS estimates that 8.8 percent of respondents ages 16 to 59 had used illicit drugs (almost three million people) and that 3 percent had used a Class A drug in the last year (around a million people). Neither estimates were statistically significantly different from the 2009/10 BCS. Regarding a trend, since 1996, when BCS drug-use measurement began, trends in levels of last-year drug use among adults ages 16-59 show that last-year use of any illicit drug has declined from 11.1 percent in 1996 to 8.8 percent in the 2010/11 BCS. This decline was mainly due to a decrease in the use of cannabis since the 2003.04 survey. Although the long-term trend indicates relatively constant levels of Class A drug use overall, within this category there were increases in powder cocaine use between the 1996 and 2010/11 BCS. In contrast, there were decreases during the same period in the use of hallucinogens. Among adults 16-59 years old, the level of any illicit drug use was highest among the 16-19 age group (23 percent, and Class A drug use was highest among 20-24 year olds (7.8 percent) compared with other age groups. 8 figures, 8 tables, and appended 5-item bibliography and a discussion of the measurement of drug use by the BCS