Another co-author, Dr. Paul Watkins of the University of North Carolina, said he's less worried than Kaplowitz, noting that acetaminophen, the active ingredient in Tylenol, has been used for 50 years and has a good safety record.

The maker of Tylenol, McNeil Consumer & Specialty Pharmaceuticals, said its own research found much lower rates of abnormal liver results. The company's studies tracked high-dose users over longer periods than did the new study.

"It doesn't lead to liver disease and it usually resolves as patients continue to take acetaminophen," said Dr. Edwin Kuffner, senior director of medical affairs at McNeil.

Data from a survey of 43,000 U.S. adults heighten concerns that early alcohol use, independent of other risk factors, may contribute to the risk of developing future alcohol problems. Those who began drinking in their early teens were not only at greater risk of developing alcohol dependence at some point in their lives, they were also at greater risk of developing dependence more quickly and at younger ages, and of developing chronic, relapsing dependence. Among all respondents who developed alcoholism at some point, almost half (47 percent) met the diagnostic criteria for alcohol dependence (alcoholism) by age 21.

The associations between early drinking and later problems held even after investigators controlled for other risk factors for dependence, adding to concerns that drinking at a young age might raise the risk of future alcohol problems rather than being an identifying feature of young people predisposed to risky behavior. The study appears in the July issue of Archives of Pediatrics & Adolescent Medicine (volume 160, pages 739-746).

Elias A. Zerhouni, M.D., director of the NIH, said, “This is a very good example of how insights gained from health research can inform public policy. Converging research suggests that youthful drinking is associated with an increased risk of long-term, not just acute, health consequences.”

Scientists at the Boston University School of Public Health and Youth Alcohol Prevention Center, led by Dr. Ralph Hingson*, carried out the analysis using data from the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), a representative survey of the U.S. civilian noninstitutionalized population aged 18 years and older.

NESARC involved face to face interviews with adults ages 18 and older. The survey used questions based on diagnostic criteria for alcohol abuse and alcohol dependence from the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (DSM-IV). In the study, “starting to drink” meant the age when respondents first drank alcohol, not counting tastes or sips.

NIAAA Director Dr. Ting-Kai Li said “this work underscores the need for research to clarify how early drinking relates to the risk of lifetime alcohol problems. In particular, it is important to learn whether early alcohol use may affect the developing brain in ways that increase vulnerability to dependence.”

In results that echo earlier studies, of those individuals who began drinking before age 14, 47 percent experienced dependence at some point, vs. 9 percent of those who began drinking at age 21 or older. In general, each additional year earlier than 21 that a respondent began to drink, the greater the odds that he or she would develop alcohol dependence at some point in life. While one quarter of all drinkers in the survey started drinking by age 16, nearly half (46 percent) of drinkers who developed alcohol dependence began drinking at age 16 or younger.

New findings showed that among all drinkers, early drinking was associated not only with a higher risk of developing alcoholism at some point, but also within 10 years of first starting to drink, before age 25, and within any year of adult life. Early drinking was also associated with increased risk of having multiple episodes of alcoholism. Further, among respondents who had had alcohol dependence at some point, those who began drinking young had episodes of longer duration and with a wider range of symptoms than those who started later.

Previous research has established the link between early onset of drinking and lifetime diagnosis of alcoholism. Key to understanding the relationship between early drinking and alcoholism risk is whether the act of drinking while young raises lifetime risk, or whether early drinking reflects an underlying predisposition for risky behavior in particular young people. In the latter case, early drinking would be considered a marker identifying individuals already at risk for developing alcoholism. In this study, investigators attempted to account for factors — such as family history of alcoholism, childhood antisocial behavior and depression, and smoking and drug use — known to be associated with higher risk. Even controlling for a number of risk factors and the effects of age differences among respondents, early drinking was associated with an increased risk of lifetime alcohol diagnosis.

In calculating the impact of early drinking on the risk of experiencing alcoholism, the study used statistical methods that account for the fact that older respondents have had a longer window of opportunity to develop alcoholism than younger respondents. The risk of those who began drinking before age 14 was multiplied by a factor (or “hazard ratio”) of 1.78 relative to those who started drinking at age 21 or older.

The recently released 2005 Youth Risk Behavior Survey — conducted by the Centers for Disease Control and Prevention — found that among high school students nationwide, 26 percent had drunk alcohol (other than a few sips) for the first time before age 13.

The authors conclude that the results of both studies support the need to take measures to delay alcohol consumption by underage youth. Dr. Hingson said, “This analysis suggests that interventions that delay drinking onset may not only reduce the acute consequences of drinking among youth, but may help reduce alcohol dependence among adolescents and adults. It’s an important public health issue for longitudinal research to resolve.”

The National Institute on Alcohol Abuse and Alcoholism, part of the National Institutes of Health, is the primary U.S. agency for conducting and supporting research on the causes, consequences, prevention, and treatment of alcohol abuse, alcoholism, and alcohol problems and disseminates research findings to general, professional, and academic audiences. Additional alcohol research information and publications are available at www.niaaa.nih.gov.

The National Institutes of Health (NIH) — The Nation's Medical Research Agency — includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.