Adult marijuana abuse increased during 1990's

In an article appearing in the May 5 issue of the Journal of the American Medical Association (JAMA), addiction researchers at the National Institutes of Health compared marijuana use in the U.S. adult population in 1991 - 92 and 2001 - 02. They found that the number of people reporting use of the drug remained substantially the same in both time periods, but the prevalence of marijuana abuse or dependence increased markedly. This new study showed that increases in the prevalence of abuse or dependence were most notable among young African-American men and women and young Hispanic men.

This is the first study to assess long-term trends in marijuana abuse and dependence in the United States using the most up-to-date classification system - the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV).

The researchers from the National Institute on Drug Abuse (NIDA) and the National Institute on Alcohol Abuse and Alcoholism (NIAAA) compared trends in marijuana use, abuse, and dependence using the DSM-IV categories. The DSM defines marijuana abuse as repeated instances of use under hazardous conditions; repeated, clinically meaningful impairment in social/occupational/educational functioning; or legal problems related to marijuana use. Marijuana dependence is defined as increased tolerance, compulsive use, impaired control, and continued use despite physical and psychological problems caused or exacerbated by use.

"Marijuana is the most commonly used illegal substance in the United States, and its use is associated with educational underachievement, reduced workplace productivity, motor vehicle accidents, and increased risk of use of other substances," says NIDA Director Dr. Nora D. Volkow. "This study suggests that we need to develop ways to monitor the continued rise in marijuana abuse and dependence and strengthen existing prevention and intervention efforts, particularly developing and implementing new programs that specifically target African-American and Hispanic young adults."

Dr. Wilson Compton, Director of the Division of Epidemiology, Services and Prevention Research at NIDA, Dr. Bridget Grant at NIAAA, and their colleagues evaluated data from two large, national epidemiologic surveys conducted 10 years apart - the National Longitudinal Alcohol Epidemiologic Survey (NLAES) and the National Epidemiological Survey on Alcohol and Related Conditions (NESARC).

A total of 42,862 men and women ages 18 years and older participated in the 1991 - 1992 NLAES study, which was conducted by the NIAAA under the leadership of Dr. Grant. She was also the principal architect for the 2001 - 2002 NESARC study, which included 43,093 similarly aged men and women. Both surveys included the same core questions to assess marijuana use, abuse, and dependence.

"The value of well-designed and well-executed epidemiologic studies is that they point to where problems exist and where additional research and resources must be directed. In addition to the findings about marijuana, we look forward to learning more about alcohol disorders - indeed, about other mental health disorders, as well - from the same data set," explains Dr. Ting-Kai Li, Director, NIAAA.

"The results of our study show that use of marijuana remained stable in 2001 - 2002 compared to 1991 - 1992; however, there were significant increases in marijuana abuse or dependence, especially in certain minority subgroups," says Dr. Compton. "Overall, marijuana abuse or dependence rose by 22 percent from 1991 - 1992 to 2001 - 2002. This means that there were approximately 800,000 more adults in the United States with marijuana abuse or dependence in 2001 - 2002. Furthermore, marijuana abuse or dependence was more common among Whites than among minorities in 1991 - 1992, but by 2001 - 2002 the differences in abuse and dependence rates among the different ethnic groups had narrowed considerably. This change was due to increases of 224 percent among young African-American men and women aged 18 - 29, and 148 percent among young Hispanic men aged 18 - 29."

The increase in potency of marijuana over the last decade may be partly responsible for the drug's increased abuse and dependence, particularly since marijuana use patterns have not changed over this period. However, no single factor can account entirely for the increases seen in minority populations, the authors report. Numerous cultural, psychosocial, economic, and lifestyle factors likely play roles.