The 2002 National Survey on Drug Use and Health also said nearly 20 million people were current users of illegal drugs, with such use highest among young adults.
More than one in five 18- to 25-year-olds, or 20.2 percent of young adults, were current users, with marijuana being the substance of choice, the survey said.
Current users are those who said they had used an illegal drug within the past month.
The Substance Abuse and Mental Health Services Administration, a division of the Department of Health and Human Services, conducts the yearlong study. Formerly called the National Household Survey on Drug Abuse, it is the largest of its kind by the government. Results are based on interviews with nearly 70,000 people ages 12 and over and from all 50 states.
The 2001 survey found 15.9 million illegal drug users in the United States, including one in five young adults — those in the 18 to 25-year-old age category.
About 3.5 million people received some kind of treatment last year for alcohol or use of illicit drugs — marijuana, cocaine, pain relievers or heroin, or less than one-sixth of those who abused drugs and alcohol. Most of those, or 2.2 million, were treated for alcohol.
Among youths, nearly 12 percent of 12- to 17-year-olds were current users of illicit drugs.
Just 5.8 percent of adults aged 26 or older reported using illegal drugs.
Rates of current illegal drug use were highest among American Indians/Alaska natives, 10.1 percent; people of two or more races, 11.4 percent; and jobless adults aged 18 or older, 17.4 percent.
Other survey findings:
- The percentage of youths who said they ever had used marijuana declined slightly, from 21.9 percent in 2001 to 20.6 percent.
- Young adults who ever had used marijuana increased slightly, from 53 percent in 2001 to 53.8 percent last year.
- The percentage of youths who ever had used cocaine increased slightly, from 2.3 percent in 2001 to 2.7 percent.
- Young adults who ever had used cocaine also increased slightly, from 14.9 percent in 2001 to 15.4 percent in 2002.
- About 17.5 million adults 18 years or older suffered from a serious mental illness in 2002. The rates were highest among 18- to 25-year-olds, and lowest for people age 50 and over.
- Nearly half, or 8.4 million, of those suffering from a serious mental illness received treatment.