Methods
Sample and Procedures
We used data from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). Briefly, this nationally representative study of the US population was conducted in 2001–2002 and 2004–2005 among non-institutionalized adults (≥18 years of age) residing in households and group quarters. African-Americans, Hispanics, and individuals aged 18–24 years were oversampled. All participants were interviewed at home by trained lay interviewers who received extensive training and supervision. After complete description of the study to the participants, written informed consent was obtained. All procedures, including informed consent, received full ethical review and approval from the U.S. Census Bureau and U.S. Office of Management and Budget. Of the 43,093 respondents in 2001–2002, 34,653 were re-interviewed in 2004–2005. The response rate in 2001–2002 was 81% and 86.7% in 2004–2005. For the present analysis we combined data from 2001–2002 and 2004–2005 and studied individuals with lifetime illegal drug use disorders and their access to treatment. Data were weighted at wave 2 to account for differential loss to follow-up and to be representative of the target population. This analysis includes 34,653 respondents who completed interviews at wave 1 and wave 2.
Psychiatric Disorders
Participants' lifetime psychiatric disorders were measured using the NIAAA Alcohol Use Disorder and Associated Disabilities Interview Schedule (AUDADIS), a structured interview designed to measure psychiatric disorders and associated conditions in large scale surveys in 2001–2002 and 2004–2005. To meet criteria for a lifetime psychiatric diagnosis participants had to have a positive diagnosis at either NESARC wave (or both). Lifetime illegal drug use disorders were defined as abuse or dependence meeting DSM-IV criteria for any of the following illegal drugs: opioids, sedatives, tranquilizers, amphetamine, cocaine, inhalants/solvents, hallucinogens, cannabis, and heroin.
Lifetime mood disorders were defined as major depression, dysthymia, manic disorder or hypomanic disorder meeting DSM-IV criteria; lifetime anxiety disorders were defined as panic disorder with or without agoraphobia, agoraphobia with no history of panic disorder, social phobia, specific phobia, or generalized anxiety meeting DSM-IV criteria.
Treatment for Illegal Drug Use Disorders
We divided the study population into four groups: 1) illegal drug use disorder without comorbid mood or anxiety disorders (n = 244), 2) illegal drug use disorder with comorbid mood disorder only (n = 264), 3) illegal drug use disorder with comorbid anxiety disorder only (n = 110), 4) illegal drug use disorder with comorbid mood and anxiety disorders (n = 496).
Study Outcomes
We examined two study outcomes: treatment for illegal drug use disorders among all those with an illegal drug use disorder and perceived unmet need for treatment among those having not received treatment. Service use was ascertained for each drug of abuse by the following question: "Have you ever gone anywhere or seen anyone for a reason that was related in any way to your use of medicines or drugs - a physician, counselor, Narcotics Anonymous, or any other community agency or professional?" Participants who answered positively were additionally asked to describe the type of treatment they received (outpatient, inpatient, detoxification, rehabilitation, social services). Moreover, participants were asked about perceived unmet need for treatment: "Was there ever a time when you thought you should see a doctor, counselor, or other health professional or seek any other help for your drug use, but you didn't go?" Participants who met criteria for perceived unmet need for treatment were further asked about reasons for not receiving treatment. Variables ascertaining treatment for illegal drug use disorders and perceived unmet need for treatment were dichotomized. For the purpose of our descriptive analyses participants were split into four groups: 1) those who had an illegal drug use disorder and received treatment (n = 350); those with an illegal drug use disorder who did not receive treatment (n = 764); 2) those who did not receive treatment for an illegal drug use disorder and perceived an unmet need for treatment (n = 127); 3) those who did not receive treatment for an illegal drug use disorder and did not perceive an unmet need for treatment (n = 637).
Additionally, we studied access to treatment for illegal drug use disorders in relation to the type and number of drug of abuse.
Covariates
Socio-demographic covariates included sex (female vs. male), age (35–54, ≥55 years vs. 18–34 years), educational level (<high school degree vs. ≥ high school), marital status (divorced/separated, widowed, never married vs. married), ethnicity (African American, Other non-Caucasian vs. Caucasian) and family income dichotomized using the lowest quartile of the distribution as the cut-off ($10,000–19000 vs. ≥$20,000/year).
Statistical Analyses
Analyses examining the relationship between the presence of mood and anxiety disorders and a) treatment for an illegal drug use disorder (n = 1114) and b) perceived unmet need for treatment among participants who never received treatment for an illegal drug use disorder (n = 764) were conducted separately.
Because of a significant overlap between treatment for an illegal drug use disorder and treatment for mood (44.5%) and anxiety (28.5%) disorders, in secondary analyses we further controlled for lifetime treatment for mood and anxiety disorders. Furthermore, 74.9% of participants with lifetime illegal drug use disorder also had an alcohol-related disorder; in further analyses we controlled for comorbid alcohol-related disorder.
All analyses were carried out in a logistic regression framework using STATA/SE 12; odds ratios and 95% confidence intervals were weighted to account for sampling design. We used Taylor series estimation methods for variance estimation (STATA svy commands) to obtain proper standard error estimates for the cross-tabulations and logistic regressions.