|Home | About | Journals | Submit | Contact Us | Français|
Minority groups generally experience more disparities than whites in behavioral healthcare use. The population of racial/ethnic groups is growing faster than whites. Given increased concerns of cannabis use (CU) and its associations with health conditions, we examined national trends in cannabis use disorder (CUD) among adults aged ≥18 by race/ethnicity.
Data were from the 2005–2013 National Surveys on Drug Use and Health (N=340,456). We compared CU patterns and the conditional prevalence of CUD among cannabis users by race/ethnicity to understand racial/ethnic variations in CUD.
Approximately 1.5 % of adults met criteria for a CUD in the past year. Regardless of survey year, cannabis dependence was more common than cannabis abuse, representing 66% of adults with a CUD. Across racial/ethnic groups, the prevalence of cannabis abuse and dependence remained stable during 2005–2013. In the total adult sample, the odds of weekly CU, monthly CU, and cannabis dependence were greater among blacks, native-Americans, and mixed-race adults than whites. Among cannabis users, the odds of cannabis abuse and dependence were greater among blacks, native-Americans, and Hispanics than whites. Logistic regression controlling for age, sex, education, and survey year indicated an increased trend in monthly CU and weekly CU in the total sample and among past-year cannabis users. Younger age, male sex, and low education were associated with increased odds of cannabis dependence.
The large sample provides robust information that indicates a need for research to monitor CUD and identify culturally appropriate interventions especially for targeting minority populations.
Heavy or chronic cannabis use (CU) is associated with a wide range of health-related conditions, such as motor vehicle injuries, cognitive impairment, chronic bronchitis symptoms, cardiovascular diseases, or psychotic symptoms, that can result in healthcare use (Jouanjus et al., 2014; Volkow et al., 2014). Cannabis use disorder (CUD) is the most prevalent illicit drug use disorder in the United States. An estimated 4.2 million Americans aged ≥12 years had a CUD in the past year–representing an estimated 59% of individuals aged ≥12 years with a past-year illicit drug use disorder (Center for Behavioral Health Statistics and Quality [CBHSQ], 2015). To date, 24 states and Washington DC have medical cannabis, four states have legalized recreational CU, and another six states have legislation pending. As the wave of state-specific policies on cannabis legalization continues to spread across the nation, they could have unintended consequences (e.g., an increase in supply or use-related problems) with lasting implications for the health and social systems; Volkow et al., 2014, 2016). This study seeks to leverage national survey datasets to understand recent/active CUD among racial/ethnic groups to inform surveillance and intervention efforts.
Although the causal relationship between cannabis laws and CU problems is intrinsically difficult to determine, various reports suggest a pattern of growing CU problems. CU may impair motor coordination and driving skills, thereby increasing the risk of injuries (Institute for Behavior and Health, 2013; Volkow et al., 2014). Acute cannabis intoxication may increase motor vehicle crash risk (Rogeberg and Elvik, 2016). Brady and Li (2014) found a significant increase in the trend of cannabis-detected fatal injuries during 1999–2010, whereas the prevalence of alcohol-detected injuries remained stable. Additionally, medical cannabis laws were associated with a 10–20% increase in cannabis arrests and CU-related treatments, suggesting a possible legalization effect on CU problems (Chu, 2014). The total physical availability of medical cannabis through dispensaries and delivery services at the city-level also was positively associated with current CU and frequent use (Freisthler and Gruenewald, 2014). Cities with comparatively high levels of medical cannabis availability showed a frequent CU pattern. Likewise, Mair et al., (2015) found that the density of local cannabis dispensaries was positively associated with an increase in CU-related hospitalizations. Moreover, cannabis potency detected in confiscated samples increased steadily from about 3% in the 1980s to 12% in 2012 (Volkow et al., 2014). Preliminary data suggested that the average potency of cannabis seized by law enforcement increased by a half percentage point on average after medical cannabis legalization (Sevigny et al., 2014). The increase in the THC content raises concerns that potential adverse effects of problem CU, such as addiction, motor-vehicle accidents, or psychotic symptoms, may be intensified (Freeman and Winstock, 2015; Monte et al., 2015).
The growing concerns of CU-related problems require the analysis of large samples to monitor the CUD (cannabis abuse or dependence) prevalence, an indicator for intervention, for adult racial/ethnic populations. Minority groups in general experience greater disparities than whites in healthcare use that is related to poor health (Cook et al., 2010; NCHS, 2012). Minority populations in the United States are growing at a faster rate than the white alone population. By 2044, more than half of all Americans will be members of a minority group, and approximately 80% of the US population will be adults aged ≥18 years (Colby and Ortman, 2015). Previously, Compton et al. (2004) examined DSM-IV CUD among adults aged ≥18 in the National Longitudinal Alcohol Epidemiologic Survey and the National Epidemiologic Survey on Alcohol and Related Conditions. They found a significant increase in the CUD prevalence between 1991–1992 and 2001–2002 among blacks (0.8% vs. 1.8%) and Hispanics (0.6% vs. 1.2%), but there was little change among whites (1.3% vs. 1.4%). While the reasons for the rise in CUD among minority groups are unclear, the increase in cannabis potency, changes in perceived risk of CU, as well as environmental and socioeconomic factors (e.g., deleterious effects of acculturation on drug use, lower education) may contribute to CUD; Compton et al., 2004; Sinclair et al., 2013).
The U.S. Treatment Episode Data Set (TEDS) collects substance-involved admissions to treatment facilities that receive public funding. The recent TEDS report showed that cannabis was the most commonly identified primary illicit drug for treatment among blacks (29%), Hispanics (22%), and Asians/Pacific Islanders (21%); while the most commonly identified drug other than alcohol among whites was opiates (34%), followed by cannabis (12%) (SAMHSA, 2015). These drug-involved treatment data suggest that CUD may disproportionally affect minority groups. TEDS data reflect treatment admission encounters that can be influenced by the frequency of multiple encounters. Individual-level data thus are needed to better understand the prevalence of CUD among the growing racial/ethnic populations to inform research and clinical efforts on screening, intervention and referral to treatment for CUD. The National Survey on Drug Use and Health (NSDUH) provides the primary source of ongoing CUD data. The independent and cross-sectional 2005–2013 NSDUHs use similar designs to allow the analysis of the same variables from the pooled sample. The large sample of NSDUH also permits analysis to produce reliable CUD estimates for racial/ethnic groups with a smaller population size in the United States and to distinguish between cannabis abuse and dependence to estimate the level of CUD for racial/ethnic groups.
We examined yearly variations in the past-year CUD prevalence (abuse, dependence) in the total adult sample and the conditional CUD prevalence among past-year cannabis users to gauge the population-level CUD prevalence and determine the likelihood of CUD given use by race/ethnicity. The latter provides information to inform prevention and intervention research. In the pooled sample, we determined racial/ethnic differences in the frequency of CU (monthly, weekly), cannabis abuse, and cannabis dependence to clarify CU patterns by race/ethnicity.
We analyzed adult samples (aged ≥18 years) of public-use datasets from the 2005–2013 NSDUHs to characterize national trends in CUD by race/ethnicity. We used the 2005–2013 NSDUH datasets (n=36,965–39,133/year), as they used similar designs to allow analysis of the same variables to study CUD (SAMHSA, 2014). NSDUH is the primary national survey designed to provide ongoing estimates of drug use and drug use disorders in the United States (SAMHSA, 2006, 2014). It used multistage area probability sampling methods to select a representative sample of the civilian, noninstitutionalized population aged ≥12 years. The sample included residents of households (including shelters, rooming houses, and group homes) from the 50 states and civilians residing on military bases.
Data collection of NSDUH assessments was conducted at the respondent’s home for about an hour. Study procedures and privacy protections were carefully explained, and respondents were assured that their names would not be recorded and their responses would be kept strictly confidential. Respondents’ demographics were assessed by computer-assisted personal interviews. Substance use and health-related questions were assessed by an audio computer-assisted self-interviewing (ACASI) method to increase honest reports of sensitive behaviors (Turner et al., 1998). The ACASI allowed respondents to either read the questions on a computer screen or listen to the questions read aloud by the computer through headphones, and then entered their responses directly into the computer. Weighted response rates of household screening and interviewing for these years were 84–91% and 72–76%, respectively (SAMHSA, 2006, 2014).
NSDUH defined seven mutually exclusive groups based on respondents’ self-reported race and ethnicity: non-Hispanic white, non-Hispanic black, non-Hispanic native-American (American Indian/Alaska-native), non-Hispanic native-Hawaiian/Pacific-Islander, non-Hispanic Asian-American, mixed-race (>1 race), and Hispanic. The public-use data did not distinguish between specific racial groups of mixed-race individuals. The US census data estimated that 83% of mixed-race individuals were white in combination with ≥1 other race (black, Asian-American, native-Hawaiian/Pacific-Islander, native-American, or other) (US Census Bureau, 2011). We examined respondents’ age group, sex, and educational level to describe their key demographic and to include them as control variables in the analysis of racial/ethnic differences in CU and CUD due their association with drug use (Hasin and Grant, 2015). Survey year also was included as a covariate.
CU was defined as any self-reported illicit (nonmedical) use of cannabis/hashish. Respondents were read the following: “Marijuana is also called pot or grass. Marijuana is usually smoked—either in cigarettes called joints or in a pipe. It is sometimes cooked in food. Hashish is a form of marijuana that is also called hash. It is usually smoked in a pipe. Another form of hashish is hash oil.” The survey subsequently assessed respondents’ past-year use status, frequency of use, and CUD. Standardized assessments for past-year cannabis-specific abuse and dependence symptoms were based on DSM-IV criteria (APA, 2000). Consistent with DSM-IV, cannabis abuse included presence of ≥1 abuse symptom and absence of dependence, and cannabis dependence included presence of ≥3 dependence symptoms, regardless of the abuse status (APA, 2000). Based on this hierarchical classification, abuse was considered less-severe than dependence, and any CUD included past-year cannabis abuse or dependence (APA, 2000). To understand use pattern and CUD (Wu et al., 2012), we examined frequency of CU. We calculated the mean number of days using CU in the past year and examine different levels of use, including any CU, monthly use (≥12 days/years), and weekly CU (≥52 days/years), to understand whether racial/ethnic variations in CUD were consistent with CU patterns.
We examined distributions of key demographics of the total adult sample (aged ≥18) and the prevalence of CU and CUD. We calculated the CUD prevalence in the sample and among past-year cannabis users (conditional probability of CUD given use), respectively, by survey year for each racial/ethnic group. We conducted logistic regression analysis of the total adult sample to determine racial/ethnic and yearly variations in the prevalence of CU and CUD, respectively. Among past-year cannabis users, we examined racial/ethnic differences in weekly CU, monthly CU, and CUD. We conducted logistic regression analyses to estimate associations of race/ethnicity with weekly CU, weekly CU, and CUD among cannabis users, while adjusting for age, sex, education, and survey year to lessen for their confounding effects. All analyses took into account the NSDUH’s complex designs, such as weighting and clustering (StataCorp, 2013). All results are weighted except for sample sizes.
The total adult sample (N=340,456) included 31.97% of non-whites (11.52% Black, 13.87% Hispanic, 6.58% others). Compared with whites, all non-white groups had higher proportions of young adults (<35 years); blacks had a higher proportion of women; and non-white groups (except for Asian-American) had lower proportions of adults with a college degree.
Overall (annual average), 10.97% of adults used cannabis in the past year, 7.52% used cannabis monthly (≥12 days/year), 5.47% used cannabis weekly (≥52 days/year), and 1.47% of adults met criteria for a past-year CUD (abuse 0.50%, dependence 0.97%). Compared with whites, blacks, native-Americans, and mixed-race adults had a higher prevalence of CU, monthly CU, weekly CU, and cannabis abuse or dependence, and the prevalence of these variables was consistently lower among Asian-Americans.
Across racial/ethnic groups, there were little yearly variations in the prevalence of cannabis abuse and dependence during 2005–2013. Regardless of year, cannabis dependence was more common than abuse; blacks, native-Americans, and mixed-race adults tended to show a pattern of a higher prevalence of cannabis dependence than whites. In 2013, the CUD prevalence was higher among blacks (2.40%, 95% CI=1.80–3.21%), native-Americans (4.15%, 95% CI=2.57–6.63%), and mixed-race adults (3.50%, 95% CI=2.08–5.83%) than whites (1.30%, 95% CI=1.11–1.52%) (Figure 1a).
Overall (annual average), 13.39% of past-year cannabis users met criteria for a CUD (4.58% abuse, 8.81% dependence). Cannabis dependence was consistently more prevalent than abuse. Except for whites, there were little yearly variations in the prevalence of cannabis abuse and dependence among cannabis users during 2005–2013. The test for yearly trend was significant for CUD among white cannabis users, suggesting a declining prevalence in abuse or dependence (P<0.01). Across years, black and native-American cannabis users showed a pattern of a higher prevalence of cannabis dependence than white cannabis users. In 2013, the CUD prevalence among cannabis users was higher among black users (16.82%, 95% CI=13.14–21.28%) and native-American users (20.40%, 95% CI=11.96–32.60%) than white users (10.01%, 95% CI=8.57–11.66%) (Figure 1b).
To understand racial/ethnic differences in CU and CUD, we conducted logistic regression of any CU, monthly CU, weekly CU, and CUD (abuse, dependence, any), respectively, when adjusting for respondents’ age, sex, education, and survey year.
Compared with whites, blacks, native-Americans, and mixed-race adults had greater odds of monthly CU, weekly CU, and cannabis dependence, whereas Asian-Americans and Hispanics had lower odds of monthly CU, weekly CU, and cannabis dependence.
For both CU and CUD variables, younger age, male sex, and low education were associated with elevated odds of use, abuse, and dependence.
Compared with the prevalence in 2005, the odds of any CU, monthly CU, and weekly CU, were elevated during 2009–2013. Compared with the prevalence in 2005, the odds of cannabis dependence was elevated slightly in 2013.
Among cannabis users (n=65,879), blacks (mean=130.51 days/year) and mixed-race adults (mean=133.50 days/year) had a greater mean number of days using cannabis than whites (mean=109.27 days/year), and Asian-Americans had a lower mean days of use (mean=73.93 days/year) (P<0.05). Compared with white cannabis users (66.35%), more black (79.78%), native-American (78.91%), native-Hawaiian/Pacific-Islander (74.03%), mixed-race (72.88%) cannabis users reported monthly CU, and fewer Asian-American cannabis users (52.76%) reported monthly CU (P<0.05). A similar pattern in racial/ethnic variation was observed for weekly CU (ranging from 36.16% among Asian-American users to 60.84% among black users).
Finally, we conducted logistic regression analyses of CU and CUD among cannabis users, while adjusting for age, sex, education, and survey year.
Among cannabis users, blacks and mixed-raced adults had greater odds than whites of monthly and weekly CU; native-Americans had greater odds than whites of monthly CU; Asians had lower odds than whites of monthly CU; and native-Americans, and Hispanics had greater odds of cannabis abuse and dependence than whites.
Younger ages, male sex, and low education were associated with elevated odds of cannabis abuse and dependence, respectively.
Compared with the prevalence in 2005, the odds of monthly CU and weekly CU among cannabis users were elevated slightly over time. Compared with the prevalence in 2005, the odds of cannabis abuse among cannabis users was lowered slightly in 2013.
Adults constitute the vast majority of the US population, and state-level cannabis legalization laws are applied directly to adults. Problem CU could affect multiple domains of adults’ lives and health, such as cannabis abuse/dependence symptoms, cannabis-involved car accidents, and cardiovascular conditions as well as emergency department admissions (Asbridge et al., 2012; Blow et al., 2011; Thomas et al., 2014). Our CUD estimates from the national sample have implications for surveillance of CUD and clinical interventions. We used the largest samples (N=340,456) of adults aged ≥18 years available to study indicators of CU problems (abuse, dependence). In the population level, blacks, native-Americans, and mixed-race adults on average were more likely than whites to have a CUD; and Asian-Americans, native-Hawaiians/Pacific-Islanders, and Hispanics were less likely to have a CUD. Among cannabis users, blacks, native-Americans, and mixed-race adults had the highest prevalence of weekly CU (range: 55.02–60.84% vs. whites 47.87%). Our results of monthly and weekly CU were consistent with the CUD patterns that added support for racial/ethnic differences in CUD. These findings were in line with racial/ethnic variations in treatment admissions in the TEDS (SAMHSA, 2015). Considered jointly, problem CU (abuse or dependence) may impact healthcare use or treatment demand.
The findings of elevated odds of weekly CU and cannabis dependence among mixed-race individuals warrant research to monitor CU and CUD trends to inform intervention. The mixed-race population, especially children/adolescents, is the fastest growing population in the United States; and it is projected to increase from 8 million (2.5%) to 26 million (6.2% of the U.S. population) between 2014 and 2060, reflecting an increase of 228 % compared with an increase of 26% for the single-race population (Colby and Ortman, 2015). Although there is limited information about substance use disorders among mixed-race adults, an earlier study of youth 16–23 found that mixed-race youth had a particularly higher lifetime prevalence of illicit drug use than blacks and Hispanics (Wu et al., 2006). Recently, mixed-race adolescents were found to have a lower prevalence than whites of disapproving their peers’ CU as well as perceiving their parents’ and friends’ disapproval of adolescents’ own CU (Wu et al., 2015). In addition, disapproval of CU was associated with elevated odds of CU, and mixed-race adolescents had greater odds than white adolescents of using CU and having a past-year CUD. Because an individual’s disapproval of CU or attitudes toward use may be influenced by proximal family/social environments, and that state laws on medical or recreational cannabis may contribute to lenient CU norms (Friese and Grube, 2013; Sieving et al., 2000), future research needs to study whether contextual or community-level factors influence CU and CUD among mixed-race individuals. The TEDS has not reported treatment admissions for mixed-race individuals. The increased potency of cannabis and the fastest growing rate of the mixed-race population support the need to improve reports of substance-involved statistics for mixed-race individuals (SAMHSA, 2015).
Consistent with the TEDS data (SAMHSA, 2015), our findings reveal a need for research to elucidate factors contributing to CUD among blacks, such as community-level CU norms and blunt use (Lipperman-Kreda et al., 2014). Black race is related to an increased prevalence of blunt smoking, and blunt smoking is positively associated with cannabis abuse/dependence symptoms (Fairmam et al., 2015; Timberlake, 2013). In addition, native-Americans as a group have a poor health status and face substantial barriers to timely healthcare (e.g., low income, low education, high rates of chronic diseases) (Liao et al., 2011; US Census Bureau, 2014). We found that approximately 9% native-American adults reported CU weekly (≥52 days/year) and 3% had a CUD in the past year. However, the national survey of household residents may not fully capture the CUD prevalence on or near reservations. Descriptive data suggested that native-Americans were over-represented in the California medical cannabis patients (Reinarman et al., 2011). The county-level of medical cannabis cards and residents’ support for cannabis legalization (community CU norms) may increase residents’ ease of access to cannabis, including native-Americans (Friese and Grube, 2013). In-depth research efforts for native-Americans are warranted to inform the development of evidence-based and culturally appropriate addiction prevention and treatment approaches for this vulnerable population (Novins et al., 2016).
Finally, women admissions accounted for 27% of cannabis-involved treatment admissions in the TEDS report (SAMHSA, 2015). Similarly, we found lower odds of CU and CUD among women than men. However, women with a CUD tended to have comorbid depressive/anxiety problems, and they might present more severe cannabis withdrawal systems than men (Compton et al., 2004. Herrmann et al., 2015; Khan et al., 2013). Given that cannabis withdrawal systems are related to relapse and common outcome measures in studies of pharmacotherapies for cannabis dependence (Marshall et al., 2014), sex differences in comorbidities and manifestations of CUD symptoms warrant research to inform sex-specific or tailored treatments for CUD.
The NSDUH uses cross-sectional designs to produce national drug use estimates. Our results reflect associations, and they cannot be applied to about 2% of institutionalized or homeless individuals that are not covered by the survey’s sampling plan. All drug use estimates are based on self-reports, which may be influenced by recall or reporting errors. The NSDUH also has strengths. One unique strength is about its use of the same standardized assessments of CUD during the studied years to examine CUD over time. The NSDUH also implements consistency checks in data management to ensure data quality, and develops statistical computation and analysis weights to minimize response inconsistency and nonresponse bias (Gfroerer et al., 2002; Harrison et al., 2007).
Across the major racial/ethnic groups, we found that the majority of adults with a CUD had cannabis dependence, indicating a need for treatment. Screening, intervention, and referral to treatment efforts may target some groups with elevated odds of CUD, such as blacks, native-Americans, and mixed-race adults, as well as less educated adults. Future work can examine how legalization differentially affects racial/ethnic populations. Adjusted analyses showed a small increase in cannabis dependence in 2013 vs. 2005 and indicated an increased trend in monthly CU and weekly CU in the total adult sample and among cannabis users. The increase in cannabis potency signifies enhanced harms of chronic CU (e.g., addiction, cannabis-involved fatal accidents) (Freeman and Swift, 2016). These findings from a very large sample reinforce the need to monitor unintended consequences of cannabis laws, especially for the faster growing racial/ethnic populations.
Across racial/ethnic groups, cannabis dependence was more common than cannabis abuse.
Three minority groups had greater odds than whites of having cannabis dependence.
Three minority groups also had greater odds than whites of using cannabis weekly.
Adjusted analyses showed an increased trend in weekly cannabis use.
Low education was associated with elevated odds of cannabis dependence.
Role of the funding source: This work was made possible by research support from the U.S. National Institutes of Health (R01MD007658, R01DA019623, and UG1DA040317; PI, Li-Tzy Wu). The sponsoring agency had no further role in the study design and analysis, the writing of the report, or the decision to submit the paper for publication. The opinions expressed in this paper are solely those of the authors.
Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
*Supplementary material can be found by accessing the online version of this paper at http://dx.doi.org and by entering doi:…
Contributors: LT Wu designed research questions and wrote the drafts of the paper. H Zhu conducted data analyses under the supervision of LT Wu, and all authors contributed to critical revisions and interpretations of the findings to result in the final manuscript.
Conflicts of interest: The authors have no conflicts of interest to disclose.