What Is 

Comorbidity?

from the director:

Comorbidity is a topic that our stakeholders––patients, family members, health 

care professionals, and others––frequently 

ask about. It is also a topic about which 

we have insufficient information, and so it 

remains a research priority for NIDA. This 

Research Report provides information on 

the state of the science in this area. And 

although a variety of diseases commonly 

co-occur with drug abuse and addiction 

(e.g. HIV, hepatitis C, cancer, cardiovascular 

disease), this report focuses only on the 

comorbidity of drug use disorders and other 

mental illnesses.*

To help explain this comorbidity, we need 

to first recognize that drug addiction is a 

mental illness. It is a complex brain disease 

characterized by compulsive, at times 

uncontrollable drug craving, seeking, and 

use despite devastating consequences—

behaviors that stem from drug-induced 

changes in brain structure and function. 

These changes occur in some of the same 

brain areas that are disrupted in various 

other mental disorders, such as depression, 

anxiety, or schizophrenia. It is therefore not 

surprising that population surveys show a 

high rate of co-occurrence, or comorbidity, 

between drug addiction and other mental 

illnesses. Even though we cannot always 

prove a connection or causality, we do 

know that certain mental disorders are 

established risk factors for subsequent 

drug abuse—and vice versa. 

It is often difficult to disentangle the overlapping symptoms of drug addiction and 

other mental illnesses, making diagnosis 

and treatment complex. Correct diagnosis is critical to ensuring appropriate and 

effective treatment. Ignorance of or failure 

to treat a comorbid disorder can jeopardize 

a patient’s chance of success. We hope 

that our enhanced understanding of the 

common genetic, environmental, and 

neural bases of these disorders—and the 

dissemination of this information—will lead 

to improved treatments for comorbidity and 

will diminish the social stigma that makes 

patients reluctant to seek the treatment 

they need.

Nora D. Volkow, M.D.

Director

National Institute on Drug Abuse

Comorbidity: 

Addiction and Other Mental Illnesses

Is there a relationship 

between childhood 

ADHD and later drug 

abuse? See page 2.

When two disorders or illnesses occur in the same 

person, simultaneously or sequentially, they 

are called comorbid. Comorbidity also implies 

interactions between the illnesses that affect the course and 

prognosis of both. 

*Drug abuse and drug dependence, or addiction, are considered drug use disorders—a 

subgroup of mental disorders—when they meet the diagnostic criteria delineated in the 

Diagnostic and Statistical Manual of Mental Disorders (DSM). Drug dependence, as DSM 

defines it, is synonymous with the term “addiction,” which will be used preferentially in 

this report. Since the focus of this report is on comorbid drug use disorders and other 

mental illnesses, the terms “mental illness”/“mental disorders” will refer here to disorders other than substance use, such as depression, schizophrenia, anxiety, and mania. 

The terms “dual diagnosis,” “mentally ill chemical abuser,” and “co-occurrence” are also 

used to refer to drug use disorders that are comorbid with other mental illnesses. 

continued inside
Childhood ADHD 

and Later Drug 

Problems

Numerous studies have documented an increased risk for 

drug use disorders in youth with 

untreated ADHD, although some 

suggest that only a subset of 

these individuals are vulnerable: 

those with comorbid conduct 

disorders. Given this linkage, it is 

important to determine whether 

effective treatment of ADHD 

could prevent subsequent drug 

abuse and associated behavioral 

problems. Treatment of childhood 

ADHD with stimulant medications 

such as methylphenidate or amphetamine reduces the impulsive 

behavior, fidgeting, and inability 

to concentrate that characterize 

ADHD. However, some physicians 

and parents have expressed concern that treating childhood ADHD 

with stimulants might increase a 

child’s vulnerability to drug abuse 

later in life. Recent reviews of 

long-term studies of children with 

ADHD who received stimulant 

therapy found no evidence for 

this increase. However, most of 

these studies have methodological 

limitations, including small sample 

sizes and nonrandomized study 

designs, indicating that more 

research is needed, particularly 

in adolescents.

Research Report Series Comorbidity

Is Drug Addiction 

a Mental Illness?

Yes, because addiction changes 

the brain in fundamental ways, 

disturbing a person’s normal hierarchy of needs and desires and 

substituting new priorities connected with procuring and using 

the drug. The resulting compulsive 

behaviors that override the ability to control impulses despite the 

consequences are similar to hallmarks of other mental illnesses. 

In fact, the Diagnostic and 

Statistical Manual of Mental 

Disorders (DSM), the definitive 

resource of diagnostic criteria 

for all mental disorders, includes 

criteria for drug use disorders, 

distinguishing between two types: 

drug abuse and drug dependence. 

Drug dependence is synonymous 

with addiction. By comparison, 

the criteria for drug abuse hinge 

on the harmful consequences of 

repeated use but do not include 

the compulsive use, tolerance (i.e., 

needing higher doses to achieve 

the same effect), or withdrawal 

(i.e., symptoms that occur when 

use is stopped) that can be signs 

of addiction.

How Common 

Are Comorbid 

Drug Use and 

Other Mental 

Disorders?

Many people who regularly abuse 

drugs are also diagnosed with 

mental disorders and vice versa. 

The high prevalence of this comorbidity has been documented 

in multiple national population 

surveys since the 1980s. Data 

show that persons diagnosed with 

mood or anxiety disorders were 

about twice as likely to suffer also 

from a drug use disorder (abuse 

or dependence) compared with 

respondents in general. The same 

was true for those diagnosed with 

an antisocial syndrome, such as 

antisocial personality or conduct 

disorder. Similarly, persons diagnosed with drug disorders were 

roughly twice as likely to 

suffer also from mood and 

anxiety disorders (see page 3, 

“Overlapping Conditions—

Shared Vulnerability”).

Gender is also a factor in the 

specific patterns of observed comorbidities. For example, the 

overall rates of abuse and dependence for most drugs tend to be 

higher among males than females, 

and males are more likely to suffer also from antisocial personality disorder. In contrast, women 

have higher rates of amphetamine 

dependence and higher rates of 

mood and anxiety disorders. 

Addiction 

changes the 

brain, disturbing 

the normal 

hierarchy of 

needs and desires.

2 NIDA Research Report Series
Why Do Drug Use 

Disorders Often 

Co-Occur With 

Other Mental 

Illnesses?

The high prevalence of comorbidity 

between drug use disorders and other 

mental illnesses does not mean that 

one caused the other, even if it appeared 

first. In fact, establishing causality or 

directionality is difficult for several 

reasons. Some symptoms of a mental 

disorder may not be recognized until the 

illness has substantially progressed, and 

imperfect recollections of when drug 

use/abuse started can also present 

timing issues. Still, three scenarios 

deserve consideration:

1. Drugs of abuse can cause abusers to 

experience one or more symptoms of 

another mental illness. The increased 

risk of psychosis in some marijuana 

abusers has been offered as evidence 

for this possibility. 

2. Mental illnesses can lead to drug 

abuse. Individuals with overt, mild, 

or even subclinical mental disorders 

may abuse drugs as a form of selfmedication. For example, the use of 

tobacco products by patients with 

schizophrenia is believed to lessen the 

symptoms of the disease and improve 

cognition (see page 4, “Smoking and 

Schizophrenia: Self-Medication or 

Shared Brain Circuitry?”).

3. Both drug use disorders and other 

mental illnesses are caused by overlapping factors such as underlying 

brain deficits, genetic vulnerabilities, 

and/or early exposure to stress or 

trauma. 

All three scenarios probably 

contribute, in varying degrees, to how 

and whether specific comorbidities 

manifest themselves.

0%

5

10

15

20

25

Any Drug Opioids Amphetamines Cocaine Marijuana

Any mood disorder

Any anxiety disorder

All respondents

High Prevalence of Drug Abuse and Dependence 

Among Individuals With Mood and Anxiety Disorders

0%

10

20

30

40

50

Any drug use disorder

All respondents

Mood Disorders Anxiety Disorders

Because mood disorders 

increase vulnerability to 

drug abuse and addiction, 

the diagnosis and treatment of the mood disorder can reduce the risk 

of subsequent drug use. 

Because the inverse may 

also be true, the diagnosis 

and treatment of drug use 

disorders may reduce the 

risk of developing other 

mental illnesses and, if 

they do occur, lessen their 

severity or make them 

more amenable to effective treatment. Finally, 

because more than 40 

percent of the cigarettes 

smoked in this country 

are smoked by individuals 

with a psychiatric disorder, 

such as major depressive 

disorder; alcoholism; posttraumatic stress disorder 

(PTSD); schizophrenia; or 

bipolar disorder, smoking 

by patients with mental 

illness contributes greatly 

to their increased morbidity and mortality.

Higher Prevalence of Mental Disorders 

Among Patients With Drug Use Disorders

Overlapping Conditions—Shared Vulnerability

0%

10

20

30

40

50

60

70

80

Drug 

Abuse or 

Dependence

Bipolar 

Disorder

Post-Traumatic 

Stress 

Disorder

Alcohol 

Abuse or 

Dependence

Major

 Depression

No Mental 

Illness

Current smokers

Data in top two graphs reprinted from the National Epidemiologic Survey on Alcohol and Related Conditions (Conway et al., 2006). 

Data in bottom graph from the 1989 U.S. National Health Interview Survey (Lasser et al., 2000).

Higher Prevalence Smoking Among 

Patients With Mental Disorders

NIDA Research Report Series 3
Patients with schizophrenia have higher rates of alcohol, tobacco, 

and other drug abuse than the general population. Based on nationally 

representative survey data, 41 percent of respondents with past-month 

mental illnesses are current smokers, which is about double the rate of 

those with no mental illness. In clinical samples, the rate of smoking in 

patients with schizophrenia has ranged as high as 90 percent. 

 Various self-medication hypotheses have been proposed to explain 

the strong association between schizophrenia and smoking, although 

none have yet been confirmed. Most of these relate to the nicotine 

contained in tobacco products: Nicotine may help compensate for 

some of the cognitive impairments produced by the disorder and may 

counteract psychotic symptoms or alleviate unpleasant side effects of 

antipsychotic medications. Nicotine or smoking behavior may also help 

people with schizophrenia deal with the anxiety and social stigma of 

their disease. 

Research on how both nicotine and schizophrenia affect the brain has 

generated other possible explanations for the high rate of smoking 

among people with schizophrenia: The presence of abnormalities in 

particular circuits of the brain may predispose individuals to schizophrenia; increase the rewarding effects of drugs like nicotine; or reduce 

an individual’s ability to quit smoking. The involvement of common 

mechanisms is consistent with the observation that both nicotine and 

the medication clozapine (which also acts at nicotine receptors) can 

improve attention and working memory in an animal model of 

schizophrenia. Clozapine is effective in treating individuals with schizophrenia. It also reduces their smoking levels. Understanding how and 

why patients with schizophrenia use nicotine is likely to help us develop new treatments for both schizophrenia and nicotine dependence.

Smoking and Schizophrenia: SelfMedication or Shared Brain Circuitry?

Common Factors 

Overlapping Genetic Vulnerabilities. A particularly active area 

of comorbidity research involves 

the search for genes that might 

predispose individuals to develop 

both addiction and other mental 

illnesses, or to have a greater risk 

of a second disorder occurring after 

the first appears. It is estimated that 

40–60 percent of an individual’s 

vulnerability to addiction is attributable to genetics; most of this 

vulnerability arises from complex 

interactions among multiple genes 

and from genetic interactions with 

environmental influences. In some 

instances, a gene product may act 

directly, as when a protein influences how a person responds to a 

drug (e.g., whether the drug experience is pleasurable or not) or how 

long a drug remains in the body. 

But genes can also act indirectly by 

altering how an individual responds 

to stress or by increasing the likelihood of risk-taking and noveltyseeking behaviors, which could 

influence the development of both 

drug use disorders and other mental 

illnesses. Several regions of the human genome have been linked to 

increased risk of both, including associations with greater vulnerability 

to adolescent drug dependence and 

conduct disorders. 

Involvement of Similar Brain 

Regions. Some areas of the brain 

are affected by both drug use disorders and other mental illnesses. 

For example, the circuits in the 

brain that use the neurotransmitter 

dopamine—a chemical that carries 

messages from one neuron to another—are typically affected by addictive substances and may also be 

involved in depression, schizophrenia, and other psychiatric disorders. 

The rate of smoking 

in patients with 

schizophrenia has 

ranged as high as 

90 percent.

4 NIDA Research Report Series
Indeed, some antidepressants and 

essentially all antipsychotic medications target the regulation of 

dopamine in this system directly, 

whereas others may have indirect 

effects. Importantly, dopamine 

pathways have also been implicated in the way in which stress 

can increase vulnerability to drug 

addiction. Stress is also a known 

risk factor for a range of mental 

disorders and therefore provides 

one likely common neurobiological 

link between the disease processes 

of addiction and those of other 

mental disorders. 

The overlap of brain areas involved in both drug use disorders 

and other mental illnesses suggests that brain changes stemming 

from one may affect the other. For 

example, drug abuse that precedes 

the first symptoms of a mental 

illness may produce changes in 

brain structure and function that 

kindle an underlying propensity 

to develop that mental illness. If 

the mental disorder develops first, 

associated changes in brain activity may increase the vulnerability 

to abusing substances by enhancing their positive effects, reducing 

awareness of their negative effects, 

or alleviating the unpleasant 

effects associated with the mental 

disorder or the medication used to 

treat it.

The Influence of 

Developmental Stage

Adolescence—A Vulnerable 

Time. Although drug abuse and 

addiction can happen at any time 

during a person’s life, drug use

typically starts in adolescence, 

a period when the first signs of 

mental illness commonly appear. 

It is therefore not surprising that 

comorbid disorders can already 

be seen among youth. Significant 

changes in the brain occur during 

adolescence, which may enhance 

vulnerability to drug use and the 

development of addiction and other 

mental disorders. Drugs of abuse 

affect brain circuits involved in 

reward, decisionmaking, learning 

and memory, and behavioral 

control, all of which are still 

maturing into early adulthood. 

Thus, understanding the long-term 

impact of early drug exposure is a 

critical area of comorbidity research. 

Early Occurrence Increases 

Later Risk. Strong evidence has 

emerged showing early drug use to 

be a risk factor for later substance 

abuse problems; additional findings suggest that it may also be a 

risk factor for the later occurrence 

of other mental illnesses. However, this link is not necessarily a 

simple one and may hinge upon 

genetic vulnerability, psychosocial 

experiences, and/or general environmental influences. A recent 

study highlights this complexity, 

The brain continues to develop into 

adulthood and undergoes dramatic 

changes during adolescence.

One of the brain areas still maturing during adolescence is the prefrontal 

cortex—the part of the brain that enables us to assess situations, make 

sound decisions, and keep our emotions and desires under control. The 

fact that this critical part of an adolescent’s brain is still a work in progress 

puts them at increased risk for poor decisions (such as trying drugs or 

continuing abuse). Thus, introducing drugs while the brain is still developing may have profound and long-lasting consequences. 

5 20 AGES

NIDA Research Report Series 5
with the finding that frequent 

marijuana use during adolescence 

can increase the risk of psychosis 

in adulthood, but only in individuals who carry a particular gene 

variant (see sidebar, “The Influence of Adolescent Marijuana Use 

on Adult Psychosis Is Affected by 

Genetic Variables”). 

It is also true that having a 

mental disorder in childhood 

or adolescence can increase the 

risk of later drug abuse problems, as frequently occurs with 

conduct disorder and untreated 

attention-deficit hyperactivity 

disorder (ADHD). This presents a 

challenge when treating children 

with ADHD, since effective treatment often involves prescribing 

stimulant medications with abuse 

potential. This issue has generated 

strong interest from the research 

community, and although the results are not yet conclusive, most 

studies suggest that ADHD medications do not increase the risk of 

drug abuse among children with 

ADHD (see page 2, “Childhood 

ADHD and Later Drug Problems”). 

Regardless of how comorbidity 

develops, it is common in youth 

as well as adults. Given the high 

prevalence of comorbid mental 

disorders and their likely adverse impact on substance abuse 

treatment outcomes, drug abuse 

programs for adolescents should 

include screening and, if needed, 

treatment for comorbid mental 

disorders.

The high rate of comorbidity between drug abuse 

and addiction and other mental disorders argues for a 

comprehensive approach to intervention that identifies, 

evaluates, and treats each disorder concurrently.

Percentage of Individuals 

Meeting Diagnostic Criteria for 

Schizophreniform Disorder at Age 26

0%

3

6

9

12

15

Met/Met Val/Met Val/Val

No adolescent cannabis use

Adolescent cannabis use

The Influence of Adolescent 

Marijuana Use on Adult Psychosis 

Is Affected by Genetic Variables

Source: Caspi A, Moffitt TE, Cannon M, et al., 2005.

The above figure shows that variations in a gene can affect the likelihood 

of developing psychosis in adulthood following exposure to cannabis. 

The Catechol-O-Methyltransferase gene regulates an enzyme that breaks 

down dopamine, a brain chemical involved in schizophrenia. It comes in 

two forms: Met and Val. Individuals with one or two copies of the Val 

variant have a higher risk of developing schizophrenic-type disorders if 

they used cannabis during adolescence (dark bars). Those with only the 

Met variant were unaffected by cannabis use. These findings hint at the 

complexity of factors that contribute to comorbid conditions; however, 

more research is needed.

6 NIDA Research Report Series
How Can 

Comorbidity Be 

Diagnosed?

The high rate of comorbidity 

between drug use disorders and 

other mental illnesses argues for a 

comprehensive approach to intervention that identifies, evaluates, 

and treats each disorder concurrently. The needed approach calls 

for broad assessment tools that 

are less likely to result in a missed 

diagnosis. Accordingly, patients 

entering treatment for psychiatric 

illnesses should also be screened 

for substance use disorders and 

vice versa. Accurate diagnosis 

is complicated, however, by the 

similarities between drug-related 

symptoms such as withdrawal 

and those of potentially comorbid 

mental disorders. Thus, when 

people who abuse drugs enter 

treatment, it may be necessary to 

observe them after a period of abstinence in order to distinguish the 

effects of substance intoxication or 

withdrawal from the symptoms of 

comorbid mental disorders—this 

would allow for a more accurate 

diagnosis.

How Should 

Comorbid 

Conditions Be 

Treated?

A fundamental principle emerging 

from scientific research is the 

need to treat comorbid conditions 

concurrently—which can be a 

difficult proposition (see page 

9, “Barriers to Comprehensive 

Treatment of Comorbidity”). 

Patients who have both a drug 

Exposure to 

Traumatic Events 

Puts People at 

Higher Risk of 

Substance Use 

Disorders.

Emotionally traumatized people 

are at much higher risk of abusing 

licit, illicit, and prescription drugs. 

The strong association between 

PTSD and substance abuse is particularly frequent and devastating 

among military veterans, among 

whom 38,000 PTSD cases have 

been documented in the past 5 

years alone. Epidemiological studies suggest that as many as half 

of them may have a co-occurring 

substance use disorder (SUD). 

The growing incidence of PTSD 

among returning veterans poses 

an enormous challenge for a 

health care system in which PTSD 

programs don’t accept individuals 

with active SUDs while traditional 

SUD clinics defer the treatment of 

trauma-related issues. However, 

there are treatment options for 

PTSD and SUD at different stages 

of clinical validation; these include 

various combinations of psychosocial (e.g., exposure therapy) and 

pharmacologic (e.g., mood stabilizers, antianxiolitics, and antidepressants) interventions. However, 

more research is urgently needed 

to identify the best treatment 

strategies for addressing PTSD 

comorbidities, in particular depression and SUD, and to explore the 

notion that different treatments 

might be needed in response to 

civilian vs. combat PTSD.

use disorder and another mental 

illness often exhibit symptoms that 

are more persistent, severe, and 

resistant to treatment compared 

with patients who have either 

disorder alone. Nevertheless, 

steady progress is being made 

through research on new and 

existing treatment options 

for comorbidity and through 

health services research on 

implementation of appropriate 

screening and treatment within 

a variety of settings (e.g., NIDA’s 

Criminal Justice Drug Abuse 

Treatment Studies [CJ-DATS]). 

Medications

Effective medications exist for 

treating opioid, alcohol, and nicotine addiction and for alleviating 

the symptoms of many other 

mental disorders. Most of these 

medications have not been studied 

in patients with comorbidities, 

although some may prove effective 

for treating comorbid conditions. 

For example, preliminary results 

of a recent study point to the potential of using divalproex (trade 

name: Depakote)—an anticonvulsant commonly used to treat 

bipolar disorder—to treat patients 

with comorbid bipolar disorder 

and primary cocaine dependence. 

Other evidence suggests that 

bupropion (trade names: Wellbutrin, Zyban), approved for 

treating depression and nicotine 

NIDA Research Report Series 7
Examples of Promising Behavioral Therapies 

for Patients With Comorbid Conditions

Adults

Therapeutic Communities (TCs) 

TCs focus on the “resocialization” of 

the individual and use broad-based 

community programs as active components of treatment. TCs are particularly 

well suited to deal with criminal justice 

inmates, individuals with vocational 

deficits, women who need special 

protections from harsh social environments, vulnerable or neglected youth, 

and homeless individuals. In addition, 

some evidence suggests the utility of 

incorporating TCs for adolescents who 

have been in treatment for substance 

abuse and related problems.

Assertive Community Treatment 

(ACT)

ACT programs integrate the behavioral treatment of other severe mental 

disorders, such as schizophrenia, and 

co-occurring substance use disorders. 

ACT is differentiated from other forms 

of case management through factors 

such as a smaller caseload size, team 

management, outreach emphasis, a 

highly individualized approach, and an 

assertive approach to maintaining contact with patients. 

Dialectical Behavior Therapy (DBT)

DBT is designed specifically to reduce 

self-harm behaviors (such as selfmutilation and suicidal attempts, 

thoughts, or urges) and drug abuse. It is 

one of the few treatments that are effective for individuals who meet the criteria 

for borderline personality disorder.

Exposure Therapy

Exposure therapy is a behavioral 

treatment for some anxiety disorders 

(phobias, post-traumatic stress disorder 

[PTSD]) that involves repeated exposure 

to or confrontation with a feared situation, 

object, traumatic event, or memory. 

This exposure can be real, visualized, or 

simulated, and always is contained in 

a controlled therapeutic environment. 

The goal is to desensitize patients to the 

triggering stimuli and help them learn 

to cope, eventually reducing or even 

eliminating symptoms. Several studies 

suggest that exposure therapy may be 

helpful for individuals with comorbid 

PTSD and cocaine addiction, although 

retention in treatment is difficult. 

Integrated Group Therapy (IGT)

IGT is a new treatment developed specifically for patients with bipolar disorder 

and drug addiction, designed to address 

both problems simultaneously.

Adolescents

Multisystemic Therapy (MST)

MST targets key factors (attitudes, family, peer pressure, school and neighborhood culture) associated with serious 

antisocial behavior in children and 

adolescents who abuse drugs.

Brief Strategic Family Therapy (BSFT) 

BSFT targets family interactions that are 

thought to maintain or exacerbate adolescent drug abuse and other co-occurring problem behaviors. These problem 

behaviors include conduct problems 

at home and at school, oppositional 

behavior, delinquency, associating with 

antisocial peers, aggressive and violent 

behavior, and risky sexual behaviors.

Cognitive-Behavioral Therapy (CBT) 

CBT is designed to modify harmful 

beliefs and maladaptive behaviors. CBT 

is the most effective psychotherapy for 

children and adolescents with anxiety 

and mood disorders, and also shows 

strong efficacy for substance abusers. 

(CBT is also effective for adult populations suffering from drug use disorders and a range of other psychiatric 

problems.) 

8 NIDA Research Report Series
Barriers to Comprehensive 

Treatment of Comorbidity

Although research supports the need for comprehensive treatment to 

address comorbidity, provision of such treatment can be problematic for 

a number of reasons: 

•	 In the United States different treatment systems address drug use

disorders and other mental illnesses separately. Physicians are most 

often the front line of treatment for mental disorders, whereas drug 

abuse treatment is provided in assorted venues by a mix of health 

care professionals with different backgrounds. Thus, neither system 

may have sufficiently broad expertise to address the full range of 

problems presented by patients. People also use these health care 

systems differently, depending on insurance coverage and social factors. For example, when suffering from substance abuse and mental 

illness comorbidities, women more often pursue treatment services 

for mental health problems, whereas men tend to seek help through 

substance abuse treatment channels. 

•	 A lingering bias remains in some substance abuse treatment centers

against using any medications, including those necessary to treat 

serious mental disorders such as depression. Additionally, many 

substance abuse treatment programs do not employ professionals 

qualified to prescribe, dispense, and monitor medications. 

•	 Many of those needing treatment are in the criminal justice system.

It is estimated that about 75 percent of offenders in State and local 

prisons and jails have a mental health problem comorbid with substance abuse or addiction. However, adequate treatment services for 

both drug use disorders and other mental illnesses are greatly lacking 

within these settings. While treatment provision may be burdensome 

for the criminal justice system, it offers an opportunity to positively 

affect the public’s health and safety. Treatment of comorbid disorders 

can reduce not only associated medical complications, but also 

negative social outcomes by mitigating against a return to criminal 

behavior and reincarceration. 

dependence, might also help reduce craving and use of methamphetamine. Most medications have 

not been well studied in comorbid 

populations or in populations 

taking other psychoactive medications. Therefore, more research 

is needed to fully understand and 

assess the actions of combined or 

dually effective medications. 

Behavioral Therapies 

Behavioral treatment (alone or in 

combination with medications) 

is the cornerstone to successful 

outcomes for many individuals 

with drug use disorders or other 

mental illnesses. And while behavior therapies continue to be 

evaluated for use in comorbid 

populations, several strategies 

have shown promise for treating 

specific comorbid conditions (see 

page 8, “Examples of Promising 

Behavioral Therapies for Patients 

With Comorbid Conditions”). 

Most clinicians and researchers agree that broad spectrum 

diagnosis and concurrent therapy 

will lead to more positive outcomes for patients with comorbid 

conditions. Preliminary findings 

support this notion, but research 

is needed to identify the most effective therapies (especially studies focused on adolescents).

NIDA Research Report Series 9
Glossary 

Addiction: A chronic, relapsing 

disease characterized by compulsive 

drug seeking and abuse in spite of 

known adverse consequences, and 

by functional, sometimes long-lasting 

changes in the brain. 

Antisocial Personality Disorder: A 

disorder characterized by antisocial 

behaviors that involve pervasive disregard for and violation of the rights, 

feelings, and safety of others, beginning in childhood or the early teenage 

years and continuing into adulthood. 

Attention-Deficit Hyperactivity Disorder (ADHD): A disorder 

characterized by inattentiveness and/

or hyperactivity and impulsivity at a 

level far greater than others of the 

same age. 

Anxiety Disorders: Varied disorders that involve excessive or 

inappropriate feelings of anxiety or 

worry. Examples are panic disorder, 

post-traumatic stress disorder, social 

phobia, and others.

Bipolar Disorder: A mood disorder 

characterized by alternating episodes 

of depression and mania or hypomania.

Comorbidity: The occurrence of two 

disorders or illnesses in the same 

person, either at the same time 

(co-occurring comorbid conditions) or 

with a time difference between the 

initial occurrence of one and the initial occurrence of the other (sequentially comorbid conditions). 

Dopamine: A chemical (neurotransmitter) found in parts of the brain 

responsible for reward, motivation, 

and movement. 

Dual Diagnosis/Mentally Ill Chemical Abuser (MICA): Other terms 

used to describe the comorbidity of a 

drug use disorder and another mental 

illness.

Depression: A disorder marked by 

sadness, inactivity, difficulty with 

thinking and concentration, significant increase or decrease in appetite 

and time spent sleeping, feelings 

of dejection and hopelessness, and 

sometimes, suicidal thoughts or an 

attempt to commit suicide.

Major Depressive Disorder: A mood 

disorder having a clinical course of 

one or more serious depression 

episodes that last 2 or more weeks. 

Episodes are characterized by a loss 

of interest or pleasure in almost all 

activities; disturbances in appetite, 

sleep, or psychomotor functioning; 

a decrease in energy; difficulties in 

thinking or making decisions; loss of 

self-esteem or feelings of guilt; and 

suicidal thoughts or attempts.

Mania: A mood disorder characterized by abnormally and persistently 

elevated, expansive, or irritable 

mood; mental and physical hyperactivity; and/or disorganization of 

behavior.

Mental Disorder: A mental condition marked primarily by sufficient 

disorganization of personality, mind, 

and emotions to seriously impair the 

normal psychological or behavioral 

functioning of the individual. 

Addiction is a mental disorder.

Neurotransmitters: The brain’s 

chemical messengers used to transmit information between neurons.

Post-Traumatic Stress Disorder 

(PTSD): A disorder that develops 

after exposure to a highly stressful event (e.g., wartime combat, 

physical violence, or natural disaster). 

Symptoms include re-experiencing 

the trauma through flashbacks or 

recurrent nightmares, hypervigilance 

and difficulty sleeping, and avoidance 

of reminders of the event.

Psychosis: A serious mental disorder 

(e.g., schizophrenia) characterized by 

defective or lost contact with reality. 

Symptoms often include hallucinations or delusions.

Schizophrenia: A psychotic disorder characterized by symptoms that 

fall into two categories: (1) positive 

symptoms, such as distortions in 

thoughts (delusions), perception (hallucinations), and language and thinking and (2) negative symptoms, such 

as flattened emotional responses and 

decreased goal-directed behavior. 

Self-Medication: The use of a substance to lessen the negative effects 

of stress, anxiety, or other mental 

disorders (or side effects of their 

pharmacotherapy). Self-medication 

may lead to addiction and other 

drug- or alcohol-related problems.

10 NIDA Research Report Series
Biederman J, Monuteaux MC, 

Spencer T, Wilens TE, Macpherson 

HA, Faraone SV. Stimulant therapy 

and risk for subsequent substance 

use disorders in male adults with 

ADHD: A naturalistic controlled 10-

year follow up study. Am J Psychiatry 

165(5):597–603, 2008.

Brady KT, Verduin ML. Pharmacotherapy of comorbid mood, anxiety, 

and substance use disorders. Subst 

Use Misuse 40:2021–2041, 2043–

2048, 2005. 

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References

NIDA Research Report Series 11
Where can I get more scientific 

information on comorbid addiction 

and other mental illnesses?

To learn more about drug abuse 

and other mental illnesses, contact....

Where Can I Get More Scientific Information on 

Comorbid Addiction and Other Mental Illnesses?

To learn more about drug use disorders and other 

mental illnesses, or to order materials on these topics 

free of charge in English or Spanish, visit the NIDA 

Web site at www.drugabuse.gov or contact the 

DrugPubs Research Dissemination Center at 

877-NIDA-NIH (877-643-2644; 

TTY/TDD: 240-645-0228).

What’s New on the NIDA Web Site

• Information on drugs of abuse

• Publications and communications (including

NIDA Notes and Addiction Science & Clinical 

Practice journal)

• Calendar of events

• Links to NIDA organizational units

• Funding information (including program 

announcements and deadlines)

• International activities

• Links to related Web sites (access to Web sites 

of many other organizations in the field)

NIDA Web Sites

drugabuse.gov

backtoschool.drugabuse.gov

smoking.drugabuse.gov

hiv.drugabuse.gov

marijuana-info.org

clubdrugs.gov

steroidabuse.gov

teens.drugabuse.gov

inhalants.drugabuse.gov

Other Web Sites

Information on drug abuse and other mental illnesses 

is also available through these other Web sites:

• National Institute of Mental Health: 

www.nimh.nih.gov

• National Institute on Alcohol Abuse and 

Alcoholism: www.niaaa.nih.gov

• Substance Abuse and Mental Health Services 

Administration Health Information Network: 

www.samhsa.gov/shin

NIH Publication Number 08-5771

Printed December 2008

Feel free to reprint this publication.