The government says about one in five young adults last year acknowledged illicit drug use within the previous month, a rate similar to previous years.

But cocaine use declined by one-quarter and methamphetamine use by one-third as supplies dried up, leading to higher prices and reduced purity.

Drug use increased among the 50-59 age group as more baby boomers joined that category.

Overall, about 20 million people 12 or older reported using illicit drugs within the past month. Marijuana was the most popular by far.

Among adolescents, age 12 to 17, drug use dipped from 9.8 percent in 2006 to 9.5 percent last year, continuing a five-year trend.