The Natural History of Marijuana Dependence
The Natural History of Marijuana Dependence
For those who have used marijuana at least once, the relative probability of ever becoming dependent on the substance is estimated to be 9 percent. This level of risk is considerably lower than risk estimates of dependence for those who have used tobacco (32%), heroin (23%), cocaine (17%), or alcohol (15%) (Anthony et al. 1994). However, the risk of developing marijuana dependence may be higher among individuals who have smoked marijuana more frequently.
Among those who have used marijuana five or more times, the risk of dependence is estimated to be 17 percent (Hall et al. 1999). For people who use daily or near daily, the risk may increase to 33 percent (Kandel and Davies 1992).
People using marijuana who are recruited into treatment outcome studies averaged more than 10 years of near-daily use and more than six serious attempts at quitting in the past (Stephens et al. 1994b, 2000). Their use had persisted in the face of multiple forms of social, psychological, and physical impairment, and most clients perceived themselves as unable to stop. In one study of 450 clients who used marijuana chronically (Stephens et al. 2002), clients had begun smoking in early adolescence, had begun regular smoking in their late teens, had begun to experience problems by age 27, and had felt they needed treatment by age 36.
Consequences of Marijuana Use
A number of potential adverse health and behavioral effects related to both acute intoxication and chronic ingestion have been identified in epidemiological studies and clinical research (Hall 1995; Hall and Babor 2000). Several surveys of people using marijuana heavily who are not in treatment show that a majority report impairment of memory, concentration, motivation, self-esteem, interpersonal relationships, and health related to their marijuana use (Rainone et al. 1987; Roffman and Barnhart 1987). A similar profile of marijuana-related consequences is seen in samples of adults seeking treatment for marijuana dependence (Budney et al. 1998; Stephens et al. 1994b, 2000).
Exhibit VII-1 shows the frequency of self-reported problems in a group of 450 people who chronically used marijuana participating in the Marijuana Treatment Project (MTP) (Stephens et al. 2002). The table shows that clients who presented for treatment with primary marijuana dependence demonstrated a high prevalence of social, legal, medical, and psychological problems, which tend to be directly or indirectly connected with chronic marijuana use and acute marijuana intoxication (Hall et al. 1999).
Exhibit VII-1. Percentage of MTP Participants Who Endorsed
Each Marijuana Problem Item (N=450)
Has marijuana caused you % of Sample
To feel bad about your use 90.2
To have lower energy level 86.0
To procrastinate 86.0
Memory loss 76.4
To have lower productivity 75.1
Lowered self-esteem 74.2
To lack self-confidence 68.4
Withdrawal symptoms 61.1
Problems between you and your partner 58.0
Financial difficulties 48.9
Difficulty sleeping 46.0
Problems in your family 44.4
To neglect your family 38.7
Medical problems 33.6
Problems between you and your friends 26.4
To miss days at work or miss classes 19.8
To lose a job 8.2
Blackouts or flashbacks 7.6
Legal problems 7.1
Driving performance following marijuana use has been studied in several contexts. Whereas marijuana impairs performance in laboratory and simulated driving settings, studies of on-road driving performance have found only modest impairments (e.g., Chesher 1995; Robbe 1994). Controlled epidemiological studies have not established an increased risk of motor vehicle crashes among those who use only marijuana (Smiley 1999). Marijuana’s major public health significance for road safety may be to potentiate the adverse effects of alcohol on the performance of drivers who combine alcohol and marijuana intoxication (Hall and Babor 2000).
Reasonable evidence exists that marijuana use may precipitate schizophrenia in vulnerable individuals (Andreasson et al. 1987; Thornicroft 1990) and that continued use worsens the prognosis of persons with schizophrenia (Hall and Solowij 1998). People whose use of marijuana is chronic and heavy report
• Subtle impairment in the ability to focus attention and filter out complex irrelevant auditory information (Solowij et al. 1991)
• Reduced verbal and logical reasoning abilities, diminished short- and long-term memory, andaltered visual spatial ability (Lundqvist 1995)
• Mathematical and verbal expressive skill deficits (Block and Ghoneim 1993)
• Short-term deleterious impairment of executive functions (Pope et al. 1995); impairment in these abilities is likely to have an effect on occupational, academic, and interpersonal functioning.
Together, these cognitive impairments may make an individual feel isolated, misunderstood, and inadequate.
Because marijuana is most often smoked, the person who uses heavily may be at greater risk of respiratory diseases. Marijuana smoke is similar in composition to tobacco smoke and has been shown to increase chronic and acute bronchitis, cause functional alterations in the respiratory tracts, and produce morphologic changes in the airways that may precede malignant change (Halland Babor 2000; Tashkin 1999). These adverse effects appear to occur with fewer marijuana cigarettes per day and at earlier ages in people who use marijuana than in tobacco smokers. In addition, concurrent marijuana use augments many of the effects of tobacco smoking.
Approximately 50 percent of those who seek treatment for marijuana dependence also smoke tobacco (Budney et al. 1998; Stephens et al. 1993a), a rate that is significantly higher than for people of comparable age in the general population. The possibility that cancer may be induced by chronic marijuana smoking has been raised by case reports, which have described cancers of the aerodigestive system in young adults with a history of heavy marijuana use (e.g., Donald 1991; Taylor 1988). A recent epidemiological study found that chronic marijuana use may increase the risk of head and neck cancer with a strong dose-response pattern (Zhang et al. 1999).
Some studies have found maternal marijuana use to be related to preterm deliveries, low birth weights (Hatch and Bracken 1986; Zuckerman et al. 1989), and signs of neurological distress in newborns (Scher et al. 1988). Recent studies suggest subtle forms of cognitive impairment that do not become apparent until later in life in children born to mothers who use marijuana (e.g., Day et al. 1994; Richardson et al. 1995).
Research suggests that individuals can develop a dependence syndrome that is associated with recurrent psychological, social, and physical problems. The respiratory, psychological, and interpersonal problems often reported by people dependent on marijuana can lead to significant impairments in health and the quality of life.