The Monitoring the Future survey, conducted by researchers at the University of Michigan every year since 1975, measures the extent of drug, alcohol, and tobacco use among high school students as well as students’ attitudes toward drug abuse. The results of these surveys show that in the 1990s teenagers’ use of drugs (most notably marijuana) has increased, while disapproval of drug abuse has declined—a reversal of the trends of the 1980s. The surveys reveal that the percentage of high school seniors who smoke marijuana once a month increased from 11.9 percent in 1992 to 21.2 percent in 1995. At the same time, the proportion of teenagers who perceive marijuana use to be risky decreased from 79 percent in 1992 to 60.8 percent in 1995.

Many health and public policy experts find such survey results troubling. According to Alan I. Leshner, director of the National Institute...