Marijuana abuse and dependence rose in the United States in the 1990s, possibly because the substance has become more potent, according to a study released on Tuesday.

Use of marijuana by U.S. adults remained stable at about 4 percent in the 1990s, but marijuana dependence or abuse rose to 1.5 percent from 1.2 percent, according to the study published in the Journal of the American Medical Association.

That means about 800,000 more adults abused the drug or had marijuana dependency, Dr. Wilson Compton, Director of the Division of Epidemiology, Services and Prevention Research at the National Institute on Drug Abuse, said in a news release.

The increases were most notable among young black men and women and young Hispanic men, the study said.

“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,” said Dr. Nora Volkow, director of the NIDA.

The American Psychiatric Association defines abuse as repeated instances of use under hazardous conditions, legal problems related to marijuana use or meaningful impairment in school, work or social settings. Dependence is defined as increased tolerance, compulsive use, impaired control, and continued use despite physical and psychological problems caused or made worse by use.

The study used a survey of 42,862 men and women aged 18 years and older taken in 1991 and 1992 and a similar survey with 43,093 participants in 2001 and 2002.

Increased potency of marijuana over the last decade may be partly responsible for the drug’s increased abuse and dependence, the study’s authors said, adding that numerous cultural, psychosocial, economic, and lifestyle factors likely play roles.

SOURCE: Journal of the American Medical Association, May 5, 2004.