Assessing the risk of marijuana use disorder among adolescents and adults who use marijuana

Background: The changing political and social climate surrounding marijuana use, coupled with the fact that available estimates of marijuana use disorder prevalence are outdated and do not adequately represent adolescents, underscore the need for up-to-date and comprehensive prevalence estimates of marijuana use disorder. Objectives: To provide recent national estimates of marijuana use disorder as a function of usage patterns, age, and other sociodemographic, substance use, and mental health variables. Methods: Analyses of data from the 2014 National Survey on Drug Use and Health examined the prevalence of marijuana use disorder among respondents (N = 55,271) with various sociodemographic, substance use, and mental health characteristics. Logistic and multinomial regression analyses examined the correlates of marijuana use disorder as a function of these variables, with a special focus on age. Results: In 2014, 3.49% of lifetime, 11.62% of past-year, and 15.32% of past-30-day marijuana users met DSM-IV criteria for a marijuana use disorder; rates among youth generally were at least double those of adults across reported time frame and intensity of use. Regression analyses indicated that young age, black race/ethnicity, greater intensity of use, current tobacco/nicotine use, and alcohol and other drug use disorders were associated with increased odds of a marijuana use disorder. Conclusions: A significant proportion of marijuana users, especially youth, are at risk for having a marijuana use disorder, even at relatively low levels of use.     

Respiratory effects of marijuana and tobacco use in a U.S. sample

OBJECTIVE: Although a number of studies have examined the respiratory impact of marijuana smoking, such studies have generally used convenience samples of marijuana and tobacco users. The current study examined respiratory effects of marijuana and tobacco use in a nationally representative sample while controlling for age, gender, and current asthma. DESIGN: Analysis of the nationally representative third National Health and Nutrition Examination Survey (NHANES III). SETTING: U.S. households. PARTICIPANTS: A total of 6,728 adults age 20 to 59 who completed the drug, tobacco, and health sections of the NHANES III questionnaire in 1988 and 1994. Current marijuana use was defined as self-reported 100+ lifetime use and at least 1 day of use in the past month. MEASUREMENTS AND MAIN RESULTS: Self-reported respiratory symptoms included chronic bronchitis, frequent phlegm, shortness of breath, frequent wheezing, chest sounds without a cold, and pneumonia. A medical exam also provided an overall chest finding and a measure of reduced pulmonary functioning. Marijuana use was associated with respiratory symptoms of chronic bronchitis (P=.02), coughing on most days (P=.001), phlegm production (P=.0005), wheezing (P<.0001), and chest sounds without a cold (P=.02). CONCLUSION: The impact of marijuana smoking on respiratory health has some significant similarities to that of tobacco smoking. Efforts to prevent and reduce marijuana use, such as advising patients to quit and providing referrals for support and assistance, may have substantial public health benefits associated with decreased respiratory health problems.     

Executive functioning in preschool-age children prenatally exposed to alcohol,cocaine, and marijuana

BACKGROUND: Reports from clinical and experimental (animal) research converge on the suggestion that prenatal exposure to alcohol, cocaine, or marijuana undermines executive functioning (EF) and its neurological underpinnings. However, large, adequately controlled, prospective studies of alcohol and marijuana effects on EF have reported conflicting findings, and there have been no such studies of cocaine exposure. METHODS: EF was investigated in a cohort (n = 316) of 4-year-old children the majority of whose mothers had used varying combinations of cocaine, alcohol, and marijuana during pregnancy. With use of postpartum maternal report and biological assay, children were assigned to overlapping prenatal cocaine-exposed, alcohol-exposed, and marijuana-exposed groups and to complementary control groups. The postnatal environmental assessment included measures of maternal intellectual and psychosocial functioning, current drug or alcohol use, and home environment. RESULTS: The children in the alcohol-exposed group had worse tapping-inhibition performance than children in the non-alcohol-exposed group, and this effect persisted when potential confounding environmental variables, other drug variables, and concurrent verbal intelligence were controlled for. CONCLUSIONS: Prenatal alcohol is predictive of decreased EF in early childhood that could not be attributed to environmental factors. The results are discussed in terms of the age and overall high-risk status of the children.     

Current patterns of marijuana use initiation by age among US adolescents and emerging adults: implications for intervention

Background: More recent data are required for effective measures to prevent marijuana use among youth in the United States. Objective: To investigate the risk of marijuana use onset by age using the most recent data from a national sample. Methods: Data for participants (n = 26,659) aged 12–21 years from the 2013 National Survey on Drug Use and Health (NSDUH) (50.4% male, 55.6% White) were analyzed. Patterns of the risk of marijuana use initiation from birth to age of 20 years by single year of age were characterized using hazards survival models. Results: The estimated hazards of marijuana use showed unique age patterns for the overall sample and by gender and racial/ethnic groups. Up to age of 11 years, the hazards of marijuana use initiation were below 0.0500; the hazards after age of 11 years increased rapidly with two peaks at age 16 (0.1291) and 18 years (0.1496), separated by a reduction at age 17 years (0.1112). The age pattern differed significantly by gender (hazards from high to low: male, female) and race/ethnicity (hazards from high to low: multi-racial, Black, White, Hispanic, and Asian). By age of 21 years, 54.1% (56.4% for male and 51.9% for female) had initiated marijuana use with a mean onset age of 16.5 years. Conclusions: This study documented the risk of marijuana use initiation by age. Research findings suggest the timing of marijuana use prevention was no later than middle school. Additional attention is indicated to multi-racial/ethnic youth. Future interventions should be developed for both parents and adolescents, and delivered to the right target population at the right time.     

The Impact of Maternal Age on the Effects of Prenatal Alcohol Exposure on Attention

Background: Prenatal exposure to alcohol has a variety of morphologic and neurobehavioral consequences, yet more than 10% of women continue to drink during pregnancy, placing their offspring at risk for fetal alcohol spectrum disorders (FASD). Identification of at‐risk pregnancies has been difficult, in part, because the presence and severity of FASD are influenced by factors beyond the pattern of alcohol consumption. Establishing maternal characteristics, such as maternal age, that increase the risk of FASD is critical for targeted pregnancy intervention. Methods: We examined the moderating effect of maternal age on measures of attention in 462 children from a longitudinal cohort born to women with known alcohol consumption levels (absolute ounces of alcohol per day at conception) who were recruited during pregnancy. Analyses examined the impact of binge drinking, as average ounces of absolute alcohol per drinking day. Smoking and use of cocaine, marijuana, and opiates were also assessed. At 7 years of age, the children completed the Continuous Performance Test, and their teachers completed the Achenbach Teacher Report Form. Results: After controlling for covariates, stepwise multiple regression analyses revealed a negative relation between levels of prenatal binge drinking and several measures of attention. The interaction between alcohol consumption and maternal age was also significant, indicating that the impact of maternal binge drinking during pregnancy on attention was greater among children born to older drinking mothers. Conclusion: These findings are consistent with previous findings that children born to older alcohol‐using women have more deleterious effects of prenatal alcohol exposure on other neurobehavioral outcomes.     

Predictors of marijuana use and uptake among teenagers in Sydney, Australia

Information on drug-related behaviors was obtained from a random sample of teenagers aged 14 to 19 years in Sydney, Australia, interviewed in their homes in 1985 (N = 996) and 1986 (N = 756). The 1985 prevalence of current marijuana use was 10%. The predictors of marijuana use were: male sex; heavier, more frequent alcohol use; use of drugs other than alcohol, tobacco, or marijuana; marijuana use by siblings, friends, and other acquaintances; attitudes and beliefs favoring drug use; the attitude that possession of marijuana should not be a criminal offense; and the attitude that marijuana is not an important drug issue. In the 756 reinterviewed respondents, prevalence of marijuana use rose from 7% in 1985 to 9% in 1986. The rate of uptake was 6% and peaked at 12% at age 17. The predictors of uptake were: age; male sex; heavier, more frequent alcohol use; tobacco smoking; attitudes and beliefs favoring drugs use; and the attitude that marijuana smoking should be legal. Strategies to prevent marijuana use need to take into account the strong association between heavy drinking and marijuana use, the influence of drug users in the social network, and attitudes and beliefs about drugs.     

Prenatal Exposure to Alcohol and Marijuana: Effects on Motor Development of Preschool Children

Gross motor development of preschool children prenatally exposed to alcohol and marijuana was assessed as part of a longitudinal study. Most mothers in the study were light to moderate users and discontinued or decreased use of alcohol and marijuana after the first trimester of pregnancy. The women were of lower socioeconomic status, half of the sample was African-American, and most were single. Gross motor development was evaluated with balance and ball-handling items at 3 years. Balance items included walking on a line, walking on a balance beam, standing on one foot, standing on tiptoes, and stair climbing and descent. Ball-handling items included catching, throwing, and kicking a ball. Refusal to perform items was also recorded. Prenatal alcohol and marijuana exposure did not negatively affect gross motor development. The composite score on the Stanford-Binet Intelligence Scale, age at assessment, gender, and examiner were significant predictors of gross motor performance and of refusal to participate in the balance items. The ponderal index, number of siblings, current income, examiner, current maternal use of tranquilizers, and first trimester exposure to amphetamines were also significant predictors of balance skills. Gender and number of hospitalizations predicted refusal to participate in balance items, whereas hearing and vision problems predicted refusal on ball-handling items. The components of timing, speed, and fine motor control have not been addressed in this study, and therefore it is premature to conclude that there is no impact of prenatal substance use on motor development.     

Reassessing the marijuana gateway effect

Aims  Strong associations between marijuana use and initiation of hard drugs are cited in support of the claim that marijuana use per se increases youths' risk of initiating hard drugs (the 'marijuana gateway' effect). This report examines whether these associations could instead be explained as the result of a common factor—drug use propensity—influencing the probability of both marijuana and other drug use.
Design  A model of adolescent drug use initiation in the United States is constructed using parameter estimates derived from US household surveys of drug use conducted between 1982 and 1994. Model assumptions include:
(1) individuals have a non-specific random propensity to use drugs that is normally distributed in the population; (2) this propensity is correlated with the risk of having an opportunity to use drugs and with the probability of using them given an opportunity, and (3) neither use nor opportunity to use marijuana is associated with hard drug initiation after conditioning on drug use propensity.
Findings  Each of the phenomena used to support claims of a 'marijuana gateway effect' are reproduced by the model, even though marijuana use has no causal influence over hard drug initiation in the model.
Conclusions  Marijuana gateway effects may exist. However, our results demonstrate that the phenomena used to motivate belief in such an effect are consistent with an alternative simple, plausible common-factor model. No gateway effect is required to explain them. The common-factor model has implications for evaluating marijuana control policies that differ significantly from those supported by the gateway model.     

Common and drug-specific genetic influences on subjective effects to alcohol, tobacco and marijuana use

Aim To examine variation in positive and negative subjective effects to alcohol, tobacco and marijuana and covariation between these three drugs and each effect. Design Retrospective self‐reports of subjective effects were collected to estimate the genetic and environmental influences and the extent of their specificity across three drugs. Participants Data were drawn from 1299 adolescent and young adult same‐ and opposite sex twin‐ and sibling‐pairs participating in the Colorado Center for Antisocial Drug Dependence (CADD). Setting A large, collaborative, longitudinal study of substance use and antisocial behavior in community and clinical adolescents. Measurement Subjective effects were assessed using a 13‐item questionnaire that included positive and negative responses to alcohol, tobacco and marijuana. Findings Heritable influences contributed moderately (additive genetic effects 16–56%) to positive and negative subjective effects to all three drugs and did not differ for males and females. Genetic and environmental contributions to positive and negative subjective effects are largely non‐overlapping for tobacco and marijuana. Multivariate genetic modeling indicated that subjective effects to alcohol, tobacco and marijuana share a common, heritable etiology and that drug‐specific genetic influences were an important contributor to individual differences in drug response. Conclusions Results from our genetic analyses suggest that subjective effects to these commonly used and misused drugs are heritable and that the genetic and environmental influences on effects to one drug also influence subjective effects to other drugs.     

Moderate prenatal alcohol exposure and cognitive status of children at age 10

BACKGROUND: The effects of prenatal alcohol exposure (PAE) on measures of intelligence have been well documented in children with fetal alcohol syndrome. However, deficits in general intellectual ability in children with low to moderate PAE are less well understood. The objective of this study was to assess the association between moderate PAE and cognitive ability in children at age 10 controlling for other prenatal and birth factors, maternal and child psychosocial factors, and environmental characteristics. METHODS: Data were collected as part of the Maternal Health Practices and Child Development Project, a prospective study of prenatal substance use with 636 mother-child pairs. Women were assessed during each trimester of pregnancy and with their children at birth; 8 and 18 months; and 3, 6, and 10 years. Each phase included an evaluation of growth, development, cognitive, and psychological functioning. At age 10, cognitive ability was assessed using the composite score and verbal, abstract/visual, quantitative, and short-term memory area scores of the Stanford-Binet Intelligence Test, fourth edition. Maternal intellectual ability, maternal prenatal and current drug use, maternal and child psychosocial characteristics, demographics, and home environment were included in the analysis. RESULTS: A significant relation was found between alcohol exposure during the first and second trimesters and the composite score of the Stanford-Binet for African American children at age 10. Significant relations were also found for the verbal, abstract/visual, and quantitative subscales. Additional predictors of IQ at age 10 included mother's IQ, home environment, and child's report of depression. CONCLUSIONS: There is a significant association between PAE and cognitive ability at age 10 among African American offspring. There was no relation between PAE and scores on the Stanford-Binet scales among the Caucasian offspring.     

The social norms of birth cohorts and adolescent marijuana use in the United States, 1976-2007

Aims Studies of the relationship between social norms and marijuana use have generally focused on individual attitudes, leaving the influence of larger societal‐level attitudes unknown. The present study investigated societal‐level disapproval of marijuana use defined by birth cohort or by time‐period. Design Combined analysis of nationally representative annual surveys of secondary school students in the United States conducted from 1976 to 2007 as part of the Monitoring the Future study. Setting In‐school surveys completed by adolescents in the United States. Participants A total of 986 003 adolescents in grades 8, 10 and 12. Measurements Main predictors included the percentage of students who disapproved of marijuana in each birth cohort and time‐period. Multi‐level models with individuals clustered in time‐periods of observation and birth cohorts were modeled, with past‐year marijuana use as the outcome. Findings Results indicated a significant and strong effect of birth cohort disapproval of marijuana use in predicting individual risk of marijuana use, after controlling for individual‐level disapproval, perceived norms towards marijuana and other characteristics. Compared to birth cohorts in which most (87–90.9%) adolescents disapproved of marijuana use, odds of marijuana use were 3.53 times higher in cohorts where fewer than half (42–46.9%) disapproved (99% confidence interval: 2.75, 4.53). Conclusions Individuals in birth cohorts that are more disapproving of marijuana use are less likely to use, independent of their personal attitudes towards marijuana use. Social norms and attitudes regarding marijuana use cluster in birth cohorts, and this clustering has a direct effect on marijuana use even after controlling for individual attitudes and perceptions of norms.     

Craving is associated with amygdala volumes in adolescent marijuana users during abstinence

Background: Amygdala volume abnormalities have been reported in relation to craving in substance-dependent adults, but it remains unclear if these effects are seen in adolescent marijuana (MJ) users, particularly following abstinence. Objectives: The aim of this study was to examine the relationship between amygdala volume and craving during 28 days of abstinence in adolescent MJ users. Methods: MJ-using adolescents (n?=?22) aged 16–19 were recruited as part of a larger study on brain function in teen drug users. Craving measures were collected twice per week throughout a 28-day abstinence period. High-resolution anatomical magnetic resonance imaging data were collected at the end of the 28 days of confirmed abstinence. Left and right amygdala volumes were traced by hand (ICC?>?0.86). Composite scores for self-reported craving and withdrawal symptoms throughout the 28-day abstinence period were calculated to provide four composite measures of total craving, mood, sleep, and somatic complaints. Results: Results revealed that greater craving during abstinence was significantly associated with smaller left and right amygdala volumes, after controlling for age and gender. Other measures of withdrawal, including mood, somatic complaints and sleep problems, were not related to amygdala morphometry. Conclusion: These results are consistent with previous findings in adult alcohol- and cocaine-dependent individuals, who demonstrated a relationship between reduced amygdala volumes and increased craving. Future studies are needed to determine if these brain-behavior relationships are attributable to MJ use or predate the onset of substance use.     

Medicinal and recreational marijuana use by patients infected with HIV

The goal of this study was to describe and compare the prevalence, predictors and patterns of marijuana use, specifically medicinal marijuana use among patients with HIV in Ontario, Canada. Any marijuana use in the year prior to interview and self-defined medicinal use were evaluated. A cross-sectional multicenter survey and retrospective chart review were conducted between 1999 and 2001 to evaluate overall drug utilization in HIV, including marijuana use. HIV-positive adults were identified through the HIV Ontario Observational Database (HOOD), 104 consenting patients were interviewed. Forty-three percent of patients reported any marijuana use, while 29% reported medicinal use. Reasons for use were similar by gender although a significantly higher number of women used marijuana for pain management. Overall, the most commonly reported reason for medicinal marijuana use was appetite stimulation/weight gain. Whereas male gender and history of intravenous drug use were predictive of any marijuana use, only household income less than $20,000 CDN was associated with medicinal marijuana use. Age, gender, HIV clinical status, antiretroviral use, and history of intravenous drug use were not significant predictors of medicinal marijuana use. Despite the frequency of medicinal use, minimal changes in the pattern of marijuana use upon HIV diagnosis were reported with 80% of current medicinal users also indicating recreational consumption. Although a large proportion of patients report medicinal marijuana use, overlap between medical and recreational consumption is substantial. The role of poverty in patient choice of medicinal marijuana despite access to care and the large proportion of women using marijuana for pain constitute areas for further study.     

A quasi-experimental evaluation of marijuana policies and youth marijuana use

Background: Marijuana use carries risks for adolescents’ well-being, making it essential to evaluate effects of recent marijuana policies.

Objectives: This study sought to delineate associations between state-level shifts in decriminalization and medical marijuana laws (MML) and adolescent marijuana use.

Methods: Using data on 861,082 adolescents (14 to 18+ years; 51% female) drawn from 1999 to 2015 state Youth Risk Behavior Surveys (YRBS), difference-in-differences models assessed how decriminalization and MML policy enactment were associated with adolescent marijuana use, controlling for tobacco and alcohol policy shifts, adolescent characteristics, and state and year trends.

Results: MML enactment was associated with small significant reductions (OR = 0.911, 95% CI [0.850, 0.975]) of 1.1 percentage points in current marijuana use, with larger significant declines for male, Black, and Hispanic (2.7–3.9 percentage points) adolescents. Effects of MML increased significantly with each year of exposure (OR = 0.980, 95% CI [0.968, 0.992]). In contrast, decriminalization was not associated with significant shifts in use for the sample as a whole, but predicted significant declines in marijuana use among 14-year olds and those of Hispanic and other ancestry (1.7–4.4 percentage points), and significant increases among white adolescents (1.6 percentage points). Neither policy was significantly associated with heavy marijuana use or the frequency of use, suggesting that heavy users may be impervious to such policy signals.

Conclusion: As the first study to concurrently assess unique effects of multiple marijuana policies, results assuage concerns over potential detrimental effects of more liberal marijuana policies on youth use.     

The relationship of college students' use of marijuana to parental attitudes and drug-taking behavior

This study was part of an extensive survey of drug use patterns at a small private college in suburban New Jersey during the fall, 1975. Selected items from a questionnaire developed by the Inter-University Drug Survey Council of Metropolitan New York were cross-tabulated in order to examine the relationship between 379 college students' use of marijuana and their parents' attitudes and behavior relative to drug use. Significant results at the 0.01 level were found between (1) time of first marijuana use and parental attitudes toward alcohol and marijuana; (2) time of first marijuana use and parental use of barbiturates, marijuana, and pain-killers; (3) current frequency of marijuana use and parental attitudes toward alcohol and marijuana; and (4) current frequency of marijuana use and parental use of pain-killers.     

Paternal incarceration and trajectories of marijuana and other illegal drug use from adolescence into young adulthood: evidence from longitudinal panels of males and females in the United States

Aims One‐eighth of young adults in the United States report that their biological father has ever been incarcerated (FEI). This study is the first to examine associations between FEI and trajectories of substance use during the transition from adolescence into young adulthood for the US population. Design Using multi‐level modeling techniques, trajectories of marijuana and other illegal drug use are examined, with FEI as the primary independent variable. Setting Data are from the first three waves of the National Longitudinal Study of Adolescent Health, a nationally representative sample of US adolescents beginning in 1995. Participants Panels of 7157 males and 7997 females followed from adolescence (7th–12th grades) into early adulthood (ages 18–27 years). Measurements Dependent variables included an ordinal measure of marijuana frequency of use in last thirty days, and a dichotomous measure for whether respondent had any use in the last thirty days of illegal drugs such crystal meth, cocaine, heroin, hallucinogens, PCP, LSD, speed, and ecstasy. Findings Among males and females, respectively, FEI is associated with an increased frequency of marijuana use, and increased odds of any other illegal drug use. Interactions between FEI and age further reveal that FEI is associated with an accentuated trajectory (i.e. a steeper slope) of marijuana use, and an elevated risk (i.e. higher mean level) of other illegal drug use. Conclusions Analysis provides some of the first evidence that paternal incarceration is significantly associated with drug use among U.S. males and females, even after controlling for a number of family background, parental, and individual characteristics.     

Bullous lung disease due to marijuana

Background and objective:   In contrast to the well-described effects of tobacco smoking upon pulmonary emphysema, with ∼15% of smokers being affected at the age of 65 years, the effects of marijuana smoking are rarely reported and poorly understood.
Methods:   We report a series of 10 patients (mean age 41 ± 9 years, eight male, two female), who presented over a period of 12 months to our respiratory unit with new respiratory symptoms, and who admitted to regular chronic marijuana smoking (>1 year continuously). Symptoms on presentation were dyspnoea ( n  = 4), pneumothorax ( n  = 4) and chest infection ( n  = 2).
Results:   High-resolution CT revealed asymmetrical, variably sized, emphysematous bullae in the upper and mid zones. However, the CXR was normal in four patients and lung function was normal in five.
Conclusions:   Marijuana smoking leads to asymmetrical bullous disease, often in the setting of normal CXR and lung function. In subjects who smoke marijuana, these pathological changes occur at a younger age (approximately 20 years earlier) than in tobacco smokers.     

Abstinence and moderate use goals in the treatment of marijuana dependence

AIMS: The purpose of this study was to examine the influence of personal goals (abstinence or moderation) on treatment outcomes for marijuana use. Hypotheses regarding self-efficacy for goal attainment were tested. DESIGN: Adult marijuana users seeking treatment were assigned randomly to three treatment conditions: (1) cognitive-behavioral relapse prevention support group; (2) individualized brief motivational enhancement; and (3) delayed treatment control group. Follow-up assessments were conducted at 4, 7, 13 and 16 months. SETTING: University research offices. PARTICIPANTS: Participants were 291 adult marijuana users. Measurements Marijuana use, personal treatment goals and self-efficacy for achieving one's goal were assessed across the 16-month follow-up. FINDINGS: Greater marijuana related problems and dependence symptoms were associated with an initial goal of abstinence. Participants were more likely to achieve outcomes consistent with their personal goals. Participants with abstinence goals reported greater self-efficacy for goal achievement than those with moderation goals after participating in the abstinence oriented treatment; self-efficacy for goal success predicted goal achievement for both moderate use and abstinence goals. CONCLUSIONS: Marijuana users approaching an abstinence-oriented treatment varied in the extent to which they were actively seeking abstinence as the outcome. Differences in goals were predictable from severity of problems related to use. Goal preference and self-efficacy for achieving goals predicted outcomes. Future research should incorporate personal goals into treatment and assess their effects on outcomes.     

The Marijuana Check-up: reaching users who are ambivalent about change

AIMS: A brief intervention called the Marijuana Check-up (MCU) was designed to attract adult marijuana users who were experiencing adverse consequences, but who were ambivalent about change and would be unlikely to seek treatment. Our objective was to determine whether the MCU would reach the target population. DESIGN: Comparisons were made between those who enrolled in the MCU versus those who were screened but failed to follow through with enrollment on demographic, drug use and stage of change variables. Comparisons were also made between participants in the MCU and participants in a concurrently offered treatment project that targeted marijuana users who wanted to quit. SETTING: The study took place at the University of Washington in Seattle. PARTICIPANTS: Participants were adult marijuana users who telephoned and expressed interest in the MCU (n = 587). MEASUREMENT: Study variables included stage of change, frequency and duration of drug use, DSM-IV cannabis dependence and abuse diagnoses and negative consequences of marijuana use assessed via interviews and questionnaires. FINDINGS: Callers to the MCU were near-daily marijuana users, two-thirds of whom were in the pre-contemplation or contemplation stage of change. Participants who enrolled in the MCU reported fewer problems related to marijuana use and less readiness to make changes compared to those enrolled in the treatment study, despite similar levels of drug use. CONCLUSIONS: The MCU attracted and enrolled near-daily users of marijuana who experienced negative consequences but were ambivalent about making changes. The MCU potentially has a role in the continuum of care for substance abuse problems.     

Marijuana use and depression among adults: Testing for causal associations

AIM: To determine whether marijuana use predicts later development of depression after accounting for differences between users and non-users of marijuana. DESIGN: An ongoing longitudinal survey of 12 686 men and women beginning in 1979. SETTING: The National Longitudinal Survey of Youth of 1979, a nationally representative sample from the United States. PARTICIPANTS: A total of 8759 adults (age range 29-37 years) interviewed in 1994 had complete data on past-year marijuana use and current depression. MEASUREMENTS: Self-reported past-year marijuana use was tested as an independent predictor of later adult depression using the Center for Epidemiologic Studies-Depression questionnaire. Individual's propensity to use marijuana was calculated using over 50 baseline covariates. FINDINGS: Before adjusting for group differences, the odds of current depression among past-year marijuana users is 1.4 times higher (95% CI: 1.1, 1.9) than the odds of depression among the non-using comparison group. After adjustment, the odds of current depression among past-year marijuana users is only 1.1 times higher than the comparison group (95% CI: 0.8, 1.7). Similarly, adjustment eliminates significant associations between marijuana use and depression in four additional analyses: heavy marijuana use as the risk factor, stratifying by either gender or age, and using a 4-year lag-time between marijuana use and depression. CONCLUSIONS: After adjusting for differences in baseline risk factors of marijuana use and depression, past-year marijuana use does not significantly predict later development of depression. These findings are discussed in terms of their relevance for understanding possible causal effects of marijuana use on depression.