Prevalence and co-occurrence of substance use disorders and independent mood and anxiety disorders: results from the National Epidemiologic Survey on Alcohol and Related Conditions

Abstract

Background: Uncertainties exist about the prevalence and comorbidity of substance use disorders and independent mood and anxiety disorders.

Objective: To present nationally representative data on the prevalence and comorbidity of DSM-IV alcohol and drug use disorders and independent mood and anxiety disorders (including only those that are not substance induced and that are not due to a general medical condition).

Design: Face-to-face survey.

Setting: The United States.

Participants: Household and group quarters' residents.

Main Outcome Measures: Prevalence and associations of substance use disorders and independent mood and anxiety disorders.

Results: The prevalences of 12-month DSM-IV independent mood and anxiety disorders in the US population were 9.21% (95% confidence interval [CI], 8.78%-9.64%) and 11.08% (95% CI, 10.43%-11.73%), respectively. The rate of substance use disorders was 9.35% (95% CI, 8.86%-9.84%). Only a few individuals with mood or anxiety disorders were classified as having only substance-induced disorders. Associations between most substance use disorders and independent mood and anxiety disorders were positive and significant (P<.05).

Conclusions: Substance use disorders and mood and anxiety disorders that develop independently of intoxication and withdrawal are among the most prevalent psychiatric disorders in the United States. Associations between most substance use disorders and independent mood and anxiety disorders were overwhelmingly positive and significant, suggesting that treatment for a comorbid mood or anxiety disorder should not be withheld from individuals with substance use disorders.

Substance use disorders and mood and anxiety disorders are widespreadamong the general population,1-3 andare associated with substantial societal and personal costs.4-7 Furthermore,national epidemiologic surveys1-3 andnumerous clinical studies8-12 consistentlyindicate that substance use disorders and mood and anxiety disorders havestrong associations when considered on a lifetime basis. However, consensushas not been achieved on the meaning and implications of the lifetime associationof these widespread disorders. Recent work in the general population separatingpast and current disorders has clarified that intoxication or withdrawal effectsdo not entirely account for the association,13 ashad been asserted earlier.14-17 However,the nature of current or recent co-occurrence of substance and mood or anxietydisorders remains largely unexamined and poorly understood. Relative to lifetimedisorders, current co-occurrence has much more salience in its public healthand clinical implications. Thus, an important gap in knowledge about comorbidityremains.

One factor that has persistently hindered a better understanding ofthe relationship between substance use disorders and mood and anxiety disordersis diagnosis. The diagnosis of current mood or anxiety disorders among activesubstance abusers is complicated by the fact that many symptoms of intoxicationand withdrawal from alcohol and other substances resemble the symptoms ofmood and anxiety disorders. The diagnostic challenge among individuals withcurrent substance use disorders has been to devise diagnostic criteria andmeasurement techniques that differentiate between intoxication and withdrawalsymptoms and the symptoms of psychiatric disorders. This distinction is potentiallycrucial for etiologic research and treatment studies.

The DSM-IV18 representeda major departure from previous nomenclature in the importance placed on theindependent and substance-induced distinction and the clarity and specificityof the guidelines for making the distinction. Among individuals with substanceuse disorders, independent DSM-IV diagnoses of moodor anxiety disorders can be made 2 ways. First, the full mood or anxiety syndromeis established before substance use. Second, the mood or anxiety syndromepersists for more than 4 weeks after the cessation of intoxication or withdrawal.In contrast, substance-induced disorders are defined as those occurring onlyduring periods of substance use (or remitting shortly thereafter). These specificdiagnostic criteria provide a clearly defined situation for studying the associationof substance use disorders and mood and anxiety disorders that eliminatespotential diagnostic confusion arising from misdiagnosis of intoxication orwithdrawal effects.

There have been recent attempts to respond to the challenge of differentiatingindependent and substance-induced mood and anxiety disorders in clinical samples,focusing on patients with substance use disorders.14-17 Thesedifferentiations were based on the occurrence of substance use disorders ratherthan on substance use per se. In these studies, independent mood or anxietydisorders were defined as episodes occurring either before the lifetime initialonset of a substance use disorder or during a period of remission lastingat least 3 months. Remission was defined as abstinence. Other episodes ofmood or anxiety disorders were classified as substance-induced disorders.The distinction between independent and substance-induced disorders in thesestudies is problematic in several ways. First, retrospective reports of chronologicalsequences occurring many years earlier may be inaccurate. Second, basing thedistinction on substance use disorders rather than on periods of substanceuse leaves open the possibility that independent psychiatric disorders occurringduring periods of nondiagnosable substance use were missed. Third, the clinicalassessment methods in these studies did not ascertain episodes of independentmood and anxiety disorders beginning during periods of drinking or drug useand persisting longer than 1 month after the cessation of use (as specifiedin DSM-IV), thus potentially missing further independentcases. From an epidemiologic perspective, however, the most serious problemwith research on comorbidity in treated samples is that the samples of subjectsdo not represent the underlying populations. Avoiding this problem requiresepidemiologic methods.

To our knowledge, no epidemiologic survey has used the DSM-IV definitions of independent and substance-induced disorders toinvestigate comorbidity between substance use disorders and mood and anxietydisorders. The Epidemiologic Catchment Area19 survey,conducted in the early 1980s, based its diagnoses on the DSM-III,20 which had little relevanceto today's diagnostic concepts, in either the criteria for substance use disordersor the characterization of the independent and substance-induced distinction.The 1990-1992 National Comorbidity Survey (NCS)2 used DSM-III-R21 criteria. Whilethe DSM-III-R definitions of substance use disorderswere more similar to those in the DSM-IV, the handlingof substance-induced disorders was quite different. The more recent 2001-2002NCS-2 and NCS-Replication22 were intended toyield DSM-IV diagnoses. However, the NCS-2 and NCS-Replicationassessment instruments did not differentiate between independent and substance-induceddisorders, but rather asked respondents if they thought their mood or anxietydisorder was due to drinking or drug use or to a physical illness. Clearly,such opinions may differ from the intent and the specific definitions providedin the DSM-IV.

In addition, measurement of substance use disorders itself has hinderedexamination of the independent and substance-induced distinction and its effecton the comorbidity between substance use disorders and mood and anxiety disordersin the general population. In the Epidemiologic Catchment Area survey23 and the NCS,2 substancedependence was not measured as a syndrome, because clustering in time of therequired number of symptoms was not assessed. In addition, the NCS-2 and NCS-Replicationdo not yield drug-specific diagnoses, but rather produce polysubstance dependencediagnoses for which dependence criteria are met for substances as a group,but not necessarily for any specific drug. In addition, the symptoms of abuseare used as screeners for dependence, with negative responses to abuse questionsleading to a skip past questions on dependence. This leads to an undercountof about one third of the cases of dependence in the general population.24 However, more seriously, it leads to a loss of specifictypes of cases, because women with dependence are much less likely to havesymptoms of abuse than men.24 Women are alsothe individuals most likely to have mood and anxiety disorders, so missingthese cases of dependence without abuse symptoms is likely to lead to underestimatesof prevalence and comorbidity.

Because of the widespread prevalence of mood, anxiety, and substanceuse disorders and their associated disabilities and social costs, an accurateunderstanding of their comorbidity is crucial to prevention and treatment.This report presents data from a major national survey designed to overcomethe problems of previous epidemiologic surveys on comorbidity. This survey,the National Institute on Alcohol Abuse and Alcoholism's National EpidemiologicSurvey on Alcohol and Related Conditions (NESARC),25,26 coversthe comorbidity of DSM-IV substance use disordersand 9 independent mood and anxiety disorders in a nationally representativeUS sample of 43 093 respondents. To our knowledge, this is the largestcomorbidity survey ever conducted. The sample size allows for accurate estimationof current comorbidity and/or rare conditions. More important, to our knowledge,the NESARC is the first and only national survey to use the specific DSM-IV definitions of independent and substance-induceddisorders to determine if mood, anxiety, and substance use disorders are associatedeven when substance-induced disorders are ruled out. Furthermore, the NESARCoperationalized alcohol and drug dependence as syndromes, measured drug-specificdiagnoses of dependence, and ascertained alcohol and drug dependence amongall alcohol and drug users, regardless of whether they had an abuse diagnosis.The study also provides comorbidity rates separately for respondents seekingtreatment for alcohol, drug, and emotional problems because rates and patternsof comorbidity associated with the presenting complaint are most germane topracticing clinicians.