As many as 6 in 10 people who abuse drugs and alcohol also suffer from mental illnesses, according to epidemiological studies. Conversely, some 25 to 60 percent of individuals with mental illnesses also have substance abuse disorders. The overwhelming reality of these concurrent disorders presents huge challenges for drug abuse research, prevention, and treatment.

Our attempts to understand substance abuse and mental illness comorbidity are complicated by the many ways these complex conditions can develop. Research suggests that some people's genetic makeup may put them at higher risk for psychiatric and substance use disorders. In some instances, individuals with mental illness may begin to abuse drugs in attempts to alleviate distressing symptoms of the disease, putting themselves at risk for addiction. In other cases, substance abuse and its associated neurobiological changes appear to increase vulnerability to and possibly trigger mental disorders. Research funded by the National Institute of Mental Health (NIMH) and NIDA that followed more than 700 individuals from early childhood into their late twenties recently concluded that early substance abuse is associated with and significantly predicts later occurrence of psychiatric disorders, including major depressive disorder (MDD). The study's findings suggest that there are common risk factors for both substance abuse and MDD and that once abuse begins, it becomes an additional risk factor for MDD (see, "Early Use of Drugs May Lead to Later Psychiatric Disorders").

Multidisciplinary research studies can give us a better understanding of the origins and progression of comorbid substance abuse and mental disorders that will enable us to respond effectively to the problem.

Multidisciplinary research studies can give us a better understanding of the origins and progression of comorbid mental and substance abuse disorders that will enable us to respond effectively to the problem. Thus, NIDA and NIMH are increasing research to identify genetic variations that increase vulnerability to mental and substance abuse disorders and clarify how individual, social, and environmental factors influence the development and course of comorbidity. This research has the potential to bolster our ongoing efforts to develop effective approaches to preventing comorbidity and treating the vast majority of substance abuse patients who suffer from this devastating condition.

MDD, other mood disorders, conduct and personality disorders, post-traumatic stress disorder (PTSD), and schizophrenia are mental disorders that often accompany substance abuse. However, mood disorders are among the most commonly diagnosed mental illnesses in people who abuse substances. Basic research has found that drug-dependent individuals and people with depression exhibit similar alterations in brain activity. For example, drug withdrawal symptoms such as irritability, dysphoric mood, and an inability to experience pleasure are associated with changes in neurotransmission regulated by the chemical messengers dopamine and serotonin and the stress-related peptide corticotropin-releasing factor. Research has documented similar changes in the activity of these neurotransmitters in depression. To clarify the role such changes play in drug abuse and mood disorders, NIDA and NIMH recently awarded more than a dozen research grants to spur the development of new imaging compounds that will enable further exploration of the neurochemical receptors and brain regions associated with substance abuse and mental disorders. This important research could pave the way for the development of new medication strategies to treat both conditions.

Increased understanding of how biological and environmental factors affect mentally ill individuals' susceptibility to substance abuse is central to developing new programs to prevent comorbidity. We know from decades of drug abuse research that modifying factors known to foster initial drug use can prevent it from occurring and reduce the risk of progression to more severe drug abuse. We also know from NIDA's extensive program of drug abuse vulnerability research that childhood conduct disorders, anxiety disorders, and other psychiatric disorders may increase the risk of later substance abuse. While we don't know if early intervention with children with such disorders can prevent substance abuse from occurring during adolescence, several studies have found that treating children with attention-deficit/hyperactivity disorder (ADHD) with stimulant medications reduces their likelihood of developing substance abuse disorders later in life (see "Studies Link Stimulant Treatment of ADHD in Childhood to Lower Risk of Later Substance Abuse," NIDA NOTES, Vol. 18, No.1).

To help patients whose problems fall within our health missions, NIDA and NIMH have joined hands to support research that will increase fundamental knowledge about drug abuse and mental health comorbidity, advance efforts to prevent this destructive combination, and treat those already afflicted.

For the last 5 years, an ongoing NIDA program that has been exploring the links between childhood psychopathology and subsequent substance abuse has established the scientific basis for tackling this question. Last year, the program culminated in a joint NIDA/NIMH request for research aimed at identifying risk factors, causal mechanisms, and childhood mental health interventions that may prevent or inhibit later substance use. This year, the Institutes will jointly fund roughly 10 new studies under this initiative. These studies should enhance our understanding of how biological vulnerability and environmental challenges in these children's lives contribute to the chain of events that results in coexisting mental health and substance abuse disorders. In turn, this information will provide the basis for new and more effective prevention strategies.

While striving to find ways to prevent comorbidity, NIDA continues to support research to meet the treatment needs of substance-dependent patients with concurrent mental illness. Overlapping symptoms of the coexisting disorders greatly increase the difficulty of diagnosing and treating either separately. However, NIDA-funded research suggests that integrating pharmacological or behavioral therapies for mental disorders with drug abuse treatment may improve outcomes for both illnesses. Researchers have found, for instance, that giving antidepressant medications to adult patients in methadone treatment reduced their craving for drugs and their drug use as well as their comorbid mood disorder (see "Treating Mood Disorders in Drug Abuse Patients Yields Improvement in Both Conditions," NIDA NOTES, Vol. 13, No. 6). Combining an effective behavioral therapy for PTSD with cognitive behavioral therapy for cocaine abuse also has been found to produce substantial improvement in both disorders (see "Joint Treatment of PTSD and Cocaine Abuse May Reduce Severity of Both Disorders," NIDA NOTES, Vol. 18, No. 1).

That most individuals with substance abuse disorders also struggle with mental illnesses is today's reality. It does not have to be tomorrow's. To help these patients whose problems fall within our health missions, NIDA and NIMH have joined hands to support research that will increase fundamental knowledge about drug abuse and mental health comorbidity, advance efforts to prevent this destructive combination, and treat those already afflicted. NIDA's broad program of scientific investigation into the origins and pathways of comorbidity promises new prevention and treatment vehicles that can reduce the incidence of both diseases among vulnerable individuals and put those who already suffer from dual disorders on the road to recovery.

Volume 18, Number 5 (December 2003)