In a study of 6,000 high school students in New York State, Cornell University researchers found that the odds of drinking, smoking, and using marijuana were 40 percent lower among students who had participated in a school-based substance abuse prevention program in grades 7-9 than among students who had not. In 1995 near1y one out of five seniors reported complete abstinence from drugs. This represents an increase of almost 250 percent since 1980. Also in 1995, 12.8 million Americans used an illegal drug within the past month. A decrease of nearly 50 percent since 1979.

Source: Substance Abuse and Mental Health Services Administration: Prevention Works!
The 1997 National Household Survey on Drug Abuse found that the rates of use of marijuana, psychotherapeutics, cocaine, hallucinogens, and inhalants in the total population age 12 and older did not change between 1996 and 1997.
Source: White House Drug Policy Website