ANN ARBOR—Why do some young adults change their patterns of smoking, drinking, or illegal drug use after high school graduation? Their new freedoms and responsibilities explain a lot of these changes, according to a long-term nationwide study from the University of Michigan.

Young unmarried adults tend to increase their use of alcohol, marijuana, and cocaine when they leave home, often to attend college. But those kinds of drug use tend to decrease when they marry or assume other adult responsibilities.

In contrast, regardless of what they do after graduation, young people who regularly smoked cigarettes during their high school years tend to stay hooked on tobacco into their 20s and 30s, according to the study, funded since 1975 by the National Institute on Drug Abuse.

The findings are presented in the newly released book, “Smoking, Drinking, and Drug Use in Young Adulthood: The Impacts of New Freedoms and New Responsibilities,” published by Lawrence Erlbaum Associates (1997). It is authored by Jerald Bachman, Katherine Wadsworth, Patrick O’Malley, Lloyd Johnston, and John Schulenberg, all at the U-M Institute for Social Research.

The researchers analyzed questionnaire data from more than 33,000 young adults who, as high school seniors in the classes of 1976 through 1994, had participated in the U-M’s Monitoring the Future study. Then they were re-surveyed every two years after leaving high school and taking on a wide range of new roles as college students, members of the armed services, employees, spouses, and parents.

The authors examined these new freedoms and responsibilities for up to 14 years after high school graduation, and found many impacts on the use of cigarettes, alcohol, and other drugs by young adults. Among the key findings:

—Leaving the parents’ home is associated with an increase in alcohol and other drug use, particularly when young adults move into dormitories or similar housing among peers. “These new living arrangements provide freedoms from parental concerns and supervision, and typically involve many parties and other opportunities for heavy drinking and illicit drug use,” Bachman notes. “Although most survive without addiction or other permanent damage, the risk of injury to self or others is a real cause for concern.”

—Becoming engaged, marrying, and having children all are associated with substantial reductions in alcohol and illicit drug use. Couples who are living together, but not engaged or married, show no such drug use reductions, however.

—When married people divorce, the helpful effects of marriage disappear and their drug use increases. Then, when some divorced individuals remarry, the “marriage effect” reappears, reducing drug use.

—During pregnancy, women show dramatic reductions in use of alcohol and illicit drugs, and some smokers manage to quit.

—Joining the military leads to increased consumption of cigarettes and alcohol, but the use of illicit drugs drops sharply, probably as a result of vigorous efforts by the armed forces to stamp out such use.

—Despite these predictable patterns of change, drug use generally remains fairly stable over time. “If we want to know whether an individual will use a given drug during young adulthood, by far the best predictor is the individual’s use of that drug during the high school years,” the authors state.

In particular, cigarette use shows a great deal of consistency across time; most young adult users were regular daily users before they left high school.

“The typical young adult smoker lights up 10 or more times per day,” Bachman adds. “These high levels of cigarette use, and the high stability of smoking behavior across long intervals, testify to the strength and persistence of most cigarette habits.”

The present study is unique because of the large nationwide samples involved, the long (up to 14-year) time intervals included, and the fact that many different roles and experiences could be examined at the same time. For example, although college students show greater than average increases in alcohol and marijuana use, the researchers could clearly link this to the typical student living arrangements—unmarried, and residing in dormitories or apartments—rather than something else about the college experience.

Asked what broad conclusions he draws from these data, Bachman offered two observations. “First, a lot of our findings show that living with and having responsibilities to others— parents, spouses, even unborn children—can do a lot to reduce the use of drugs. Second, our findings also show that drug use patterns established in high school can have very long-lasting impacts—most notably in the case of cigarette use.”

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