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Marijuana use impairs physical and mental health, cognitive abilities, career status, and social life. Heavy marijuana use critically lowers learning skills, and daily use may result in overall reduced intellectual functioning. The National Survey on Drug Use and Health (NSDUH) asks persons aged 12 or older to report how many days they used marijuana in the past year. NSDUH also includes a series of questions to assess dependence on or abuse of marijuana and other substances. These questions are designed to measure substance dependence or abuse based on criteria specified in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). This report examines the associations between daily marijuana use and other substance use, as well as dependence on or abuse of marijuana.
In 2003, more than 25 million persons (10.6 percent) aged 12 or older reported past year use of marijuana. An estimated 3.1 million persons (1.3 percent of the population and 12.2 percent of past year marijuana users) were daily marijuana users (i.e., they used marijuana on 300 or more days in the past 12 months).
Among young adults aged 18 to 25, approximately 4.3 percent reported daily marijuana use compared with about 1.1 percent of youths aged 12 to 17 and 0.8 percent of adults aged 26 or older. Between 2002 and 2003, the number of 12 to 17 year olds reporting daily use of marijuana decreased from 358,000 to 282,000, while there were no changes in the number of daily marijuana users among 18 to 25 year olds or adults aged 26 or older.
Males were almost 3 times more likely to report daily marijuana use compared with females (2.0 vs. 0.7 percent).
A larger percentage of daily marijuana users (12.9 percent) aged 18 to 64 reported being unemployed compared with less than daily marijuana users (7.9 percent) and nonusers (3.9 percent). Persons who were less than daily marijuana users were more likely to be employed part time than daily marijuana users and nonusers.
Nearly two thirds (63.3 percent) of daily marijuana users had used another illicit drug in the past 12 months compared with less than daily marijuana users and nonusers (38.8 and 4.6 percent, respectively). Daily marijuana users also were more likely to smoke cigarettes in the past 30 days and to report heavy alcohol use in the past 30 days compared with less than daily marijuana users or nonusers.
More than half of daily marijuana users (53.3 percent) reported dependence on or abuse of alcohol or an illicit drug compared with those who were less than daily marijuana users (36.5 percent) and those who were nonusers (5.6 percent). An estimated 39.2 percent of daily marijuana users were dependent on or abused marijuana compared with 13.5 percent of less than daily marijuana users.