Lifetime Psychiatric Comorbidity of Illicit Drug Use Disorders

A second interpretation poses that one disorder may influence the onset and/or course of the other disorder. On the one hand, comorbid mental disorders may increase the risk of progression from heavy misuse of drugs to addiction. The plausibility of this interpretation is supported by order-of-onset information from both epidemiologic studies and longitudinal studies that show that the first onset of a mood, anxiety, or conduct (the precursor to ASPD) disorder usually precedes the first onset of the comorbid drug use disorder.^4,8,12-16

Individuals with mood or anxiety disorders may use drugs to self-medicate, whereas individuals with externalizing problems may, by virtue of their deviant behavior, increase their opportunities to use drugs. Of interest, mania and panic disorder with and without agoraphobia were most strongly related to specific drug use disorders involving sedatives, tranquilizers, and opiates—perhaps suggesting a preference for substances that suppress CNS activity. On the other hand, drug use may influence the onset or course of mental disorders by mediating biologic and environmental factors.

Habitual drug use alters neuroanatomy in long-lasting ways, and these changes may increase vulnerability to psychiatric disorders.^17,18 A recent review suggests that substance-induced mood and anxiety disorders are fairly common and that substance-induced psychopathology may necessitate treatment approaches that differ from disorders that are independent of drug addiction.¹¹

Third, drug use disorders and mental disorders co-occur because of shared causes that give rise to both disorders. Regarding the association between drug use disorders and ASPD, for instance, numerous researchers propose that neurobehavioral disinhibition is a common underlying vulnerability factor of both drug use disorders and antisocial syndromes.

Coupled with evidence linking self-regulatory deficits and substance use disorders to certain mesocorticolimbic brain circuits,^19,20 it is plausible that disinhibited individuals are prone to chronically misuse drugs and engage in deviant behavior because of a lack of inhibitory mechanisms to appropriately modify their conduct. The notion of a shared cause for comorbid conditions is supported by evidence from longitudinal studies^13,21,22 as well as twin studies implicating common genetic factors for all externalizing syndromes, including alcohol(Drug information on alcohol), drug, conduct, and antisocial personality disorders.^21,23-26

Clinical implications
The clinical impact of comorbidity is substantial. Comorbid disorders are more serious and chronic than single disorders,²⁷ worsen treatment prognosis,^28,29 and increase use of services and health care costs.³⁰ Substance use can have a significant impact on the course of a comorbid mental disorder and the effect may vary depending on the type of drug misused, route of administration, severity of addiction, and the presence of physical dependence. Similarly, mental disorders can impact the outcome of the addiction depending on the severity of the mental disorder, level of cognitive impairment, and availability of internal resources to develop motivation to quit.³¹ In particular, several studies have shown that co-occurring depression or ASPD worsens the course of treatment in persons who have drug use disorders.^28,29

In the treatment of patients with comorbid disorders, it is important to understand that the combinations of disorders may create new patterns of behavioral and emotional manifestations of the single disorders. Some drugs can cause depressed mood, anxiety, mania, delirium, or symptoms that may resemble a bipolar, anxiety, or psychotic disorder. On the other hand, some mental disorders can be evidenced, worsened, or masked by drug use. For example, nicotine(Drug information on nicotine), caffeine(Drug information on caffeine), marijuana, and other drugs are sometimes used to ameliorate the discomfort of a psychotic disorder or the side effects of antipsychotic medications. In fact, polysubstance use may be the most frequent drug use pattern in this population, yet associated drug use disorders may go unreported. Therefore, as a rule, all patients with mental disorders should be assessed for all drug use disorders and vice versa.³²

There is long-standing controversy about how to treat patients with concurrent drug use and other mental disorders. Should mental disorders be treated in the setting of ongoing addiction treatment? Should addiction be treated in psychiatric settings? Recent recommendations suggest that addiction should not be a barrier for the treatment of mental disorders and vice versa. Integrated treatment approaches that offer a flexible blend of mental health and addiction treatments may provide the best therapeutic effect.³³ However, because some psychiatric comorbidities can be the result of drug-induced disorders or drug abstinence,¹¹ there is no consensus about whether it is necessary to wait to rule out the primary or secondary mental disorder in order to start treatment.

The treatment plan for patients with comorbid disorders should include a comprehensive strategy to manage the mental and drug use disorders and their interactions. Psychotherapy either with or without pharmacotherapy is the most common treatment approach. In fact, some types of psychotherapy can be effective for both disorders. Interventions such as motivational interviewing, motivational enhancement therapy, contingency management, and relapse prevention can help improve the mental condition as well as help initiate drug abstinence or prevent drug use relapse. Although abstinence may not be achieved quickly, it should be the ultimate treatment goal. In the meantime, the therapy may focus on developing a therapeutic alliance, promoting treatment adherence, developing family and social support, reducing drug use, preventing the consequences of drug use, and improving mental health status.^32,34,35

Little research has been conducted testing the efficacy of medications for the treatment of comorbid disorders. The pharmacotherapy of comorbid disorders poses important clinical challenges. A medication may help reduce the symptoms of one disorder but may worsen the other; it may be contraindicated for one disorder (eg, medications with abuse liability in patients with drug use disorders), precipitate withdrawal symptoms (eg, naltrexone(Drug information on naltrexone) for alcoholism in opiate addicts), or interact with other concurrently prescribed medications (eg, disulfiram(Drug information on disulfiram) and antipsychotics).^36,37 However, some medications indicated for one disorder may help improve the comorbid disorder. A recent meta-analysis evaluating the efficacy of antidepressants for the treatment of depression and cocaine dependence suggests that when antidepressants are effective in treating depression, they also help in improving the drug use disorder.³⁸

The treatment of comorbid drug use and mental disorders can be challenging for the clinician and the health care system. Careful evaluation of the symptoms of each disorder is required, followed by formulation of an individualized integrative treatment plan that clearly weighs the risks and benefits of intervention. Given that the treatment needs of this population cut across multiple systems of care, coordinated efforts to develop true integration of services are needed to overcome existing barriers and provide adequate care to this vulnerable and needy population.