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The term dual diagnosis is used to describe the comorbid condition of a person considered to be suffering from a mental illness and a substance abuse problem. There is considerable debate surrounding the appropriateness of the term being used to describe a heterogeneous group of individuals with complex needs and a varied range of problems. The concept can be used broadly, for example depression and alcoholism, or it can be restricted to specify severe mental illness (e.g. psychosis, schizophrenia) and substance misuse disorder (e.g. cannabis abuse), or a person who has a milder mental illness and a drug dependency, such as panic disorder or generalized anxiety disorder and is dependent on opioids. Dual diagnosis is also a term used for people with an intellectual disability and diagnosed with a mental illness. Making a dual diagnosis in substance abusers is difficult as drug abuse itself often induces psychiatric symptoms, thus making it necessary to differentiate between substance induced and pre-existing mental illness.


Dual diagnosis is also used to describe a co-occurring condition in which a person is simultaneously diagnosed with an Axis I and an Axis II psychiatric disorder. While Axis I conditions are considered more or less amenable to treatments such as individual therapy and psychotropic drugs (e.g., antipsychotic, anxiolytic, and antidepressant medications), Axis II conditions are typically considered more resistant or even refractory to such treatments.

Common Axis I conditions that may be treated though drug therapy, counseling, or a combination of the two include (but are not limited to) major depressive disorder, obsessive-compulsive disorder, generalized anxiety disorder, delusional disorder, and schizophrenia. Axis II conditions are limited to mental retardation and the personality disorders such as borderline personality disorder and antisocial personality disorder.

These conditions were originally separated from the Axis I conditions to highlight their intractability to treatment, although there is some evidence to suggest that personality disorders may be managed through long-term individual therapy. The fact that autistic disorder is coded on Axis I is one of the many criticisms of the DSM-IV-TR (the diagnostic manual for mental disorders published by the American Psychiatric Association), as this falsely implies that austic disorder can be "cured" through popular but fad treatments.

Differentiating pre-existing and substance induced

Drug abuse, including alcohol and prescription drugs can induce symptomatology which resembles mental illness which can make it difficult to differentiate between substance induced psychiatric syndromes and pre-existing mental health problems. More often than not psychiatric disorders among drug or alcohol abusers disappear with prolonged abstinence. Substance induced psychiatric symptoms can occur both in the intoxicated state and also during the withdrawal state. In some cases these substance induced psychiatric disorders can persist long after detoxification, such as prolonged psychosis or depression after amphetamine or cocaine abuse. Abuse of hallucinogens can trigger delusional and other psychotic phenomena long after cessation of use and cannabis may trigger panic attacks during intoxication and with use it may cause a state similar to dysthymia. Severe anxiety and depression are commonly induced by sustained alcohol abuse which in most cases abates with prolonged abstinence. Even moderate alcohol sustained use may increase anxiety and depression levels in some individuals. In most cases these drug induced psychiatric disorders fade away with prolonged abstinence. A protracted withdrawal syndrome can also occur with psychiatric and other symptoms persisting for months after cessation of use. Benzodiazepines are the most notable drug for inducing prolonged withdrawal effects with symptoms sometimes persisting for years after cessation of use.[1]


One US study attempting to assess the prevalence of dual diagnosis found that 47% of the people they worked with, who had schizophrenia, had a substance misuse disorder at some time in their life and that the chances of developing a substance misuse disorder was significantly higher among patients suffering from a psychotic illness than in the general population without a psychotic illness.[2][3]

Another study looked at the extent of substance misuse in a group of 187 chronically mentally ill patients living in the community. According to the clinician's ratings, around a third of the sample used alcohol, street drugs, or both during the six months before evaluation.[4]

Further UK studies have shown slightly more moderate rates of substance misuse among mentally ill individuals. One study found that individuals suffering from schizophrenia showed just a 7% prevalence of problematic drug use in the year prior to being interviewed and 21% reported problematic use some time before that.[5]

Wright and colleagues identified individuals with psychotic illnesses who had been in contact with services in the London borough of Croydon over the previous 6 months. Cases of alcohol or substance misuse and dependence were identified through standardized interviews with clients and keyworkers.

Results showed that prevalence rates of dual diagnosis were 33% for the use of any substance, 20% for alcohol misuse only and 5% for drug misuse only. A lifetime history of any illicit drug use was observed in 35% of the sample.[6]


Substance use disorders can be confused with other psychiatric disease. There are diagnoses for substance-induced mood disorders and substance-induced anxiety disorders and thus such overlap can be complicated. For this reason, the DSM-IV advises that diagnoses of primary psychiatric disorders not be made in the absence of sobriety (of duration sufficient to allow for any substance-induced symptoms to dissipate).


It can be very difficult to find appropriate treatment opportunities for these people.[7] Most substance-abuse centers do not accept people with serious psychiatric conditions, and many psychiatric centers do not have expertise with substance abuse.

However, principles do exist for successful treatment of individuals with coexisting mental and substance-abuse disorders.[8] Treatment of the two disorders should be integrated, not separate, and should be a collaborative decision-making process between the treatment team and the patient. Recovery needs to be viewed as a marathon, not as a sprint, and methods and outcome goals should be explicit. Although many patients may reject medications as antithetical to substance-abuse recovery, they can be crucial to reduce paranoia, anxiety, and craving. Medications that have proven effective include opioid replacement therapies, such as life-long maintenance on methadone or buprenorphine, to minimize risk of relapse, fatality, and legal trouble amongst opioid addicts, as well as helping with cravings, baclofen for alcoholics, opioid addicts, cocaine addicts, and amphetamine addicts, to help eliminate drug cravings, and clozapine, the first atypical antipsychotic, which appears to reduce illicit drug use amongst stimulant addicts. Clozapine can cause respiratory arrest when combined with alcohol, benzodiazepines, or opioids, so it is not recommended to use in these groups.

Theories of dual diagnosis

A number of theories to explain the relationship between mental illness and substance abuse exist. Mueser et al.[9] have identified several theories that attempt to explain the mental illness-substance misuse relationship.


The causality theory suggests that certain types of substance abuse may causally lead to mental illness. Though causality in epidemiological studies can be difficult to establish, some evidence supporting a causal link between use of cannabis and later development of psychosis such as schizophrenia exist.[10]

This theory has been challenged as despite explosive increases in cannabis consumption over the past 40 years in western society, the rate of schizophrenia (and psychosis in general) has remained relatively stable.[11][12][13] For this theory to be correct, other factors which are thought to contribute to schizophrenia would have to have converged almost flawlessly to mask the effect of increased cannabis usage. However, increases in the incidence of bipolar disorder, generalized anxiety disorder, and attention deficit-hyperactivity disorder have occurred nearly simultaneously with increases in cannabis use, mirroring rapid increase—though this could be due to a broadening of the diagnostic criteria for such disorders, and/or possibly a growing tendency to "medicalize" behavioral problems and deviance.[14]

Statistics linking the incidence of schizophrenia and cannabis usage cannot ever demonstrate true causality or a lack of it (in a statistical sense, not in terms of causality as a theory on the causes of schizophrenia), however over long time periods with large samples, it appears exceedingly unlikely that cannabis usage could be causal in the development of schizophrenia. For this reason and because of the range of other viable theories regarding the causes of schizophrenia, studies claiming to show causality have tended to be met with caution by healthcare professionals.

Self-medication theory

The self-medication theory suggests that people with severe mental illnesses misuse substances in order to relieve a specific set of symptoms and counter the negative side-effects of antipsychotic medication.[15]

Khantizan proposes that substances are not randomly chosen, but are specifically selected for their effects. For example, using stimulants such as nicotine or amphetamines can be used to combat the sedation that can be caused by higher doses of certain types of (usually typical) antipsychotic medication. Conversely, some people taking medications with a stimulant effect such as the SNRI antidepressants Effexor (venlafaxine) or Wellbutrin (bupropion) may seek out benzodiazepines or opioid narcotics to counter the anxiety and insomnia that such medications sometimes evoke.

Some studies show that nicotine administration can be effective for reducing motor side-effects of antipsychotics, with both bradykinesia[16] (stiff muscles) and dyskinesia[17](involuntary movement) being prevented.

Alleviation of dysphoria theory

The alleviation of dysphoria theory suggests that people with severe mental illness commonly feel bad about themselves and that this makes them vulnerable to using psychoactive substances to alleviate these feelings. Despite the existence of a wide range of dysphoric feelings (anxiety, depression, boredom, and loneliness), the literature on self-reported reasons for use seems to lend support for the experience of these feelings being the primary motivator for drug and alcohol misuse.[18]

Multiple risk factor theory

Another theory is that there may be risk factors that can lead to both substance abuse and mental illness. Mueser hypothesizes that these may include factors such as social isolation, poverty, lack of structured daily activity, lack of adult role responsibility, living in areas with high drug availability, and association with people who already misuse drugs.[19][20]

Other evidence suggests that traumatic life events such as sexual abuse, are associated with the development of psychiatric problems and substance abuse.[21]

The supersensitivity theory

The supersensitivity theory[22] proposes that certain individuals who have severe mental illness also have biological and psychological vulnerabilities, caused by genetic and early environmental life events.

These interact with stressful life events and result in either a psychiatric disorder or trigger a relapse into an existing illness. The theory states that although anti-psychotic medication can reduce the vulnerability, substance abuse may increase it, causing the individual to be more likely to experience negative consequences from using relatively small amounts of substances.

These individuals therefore, are "supersensitive" to the effects of certain substances and suggest that individuals with psychotic illness such as schizophrenia may be less capable of sustaining moderate substance use over time without experiencing negative symptoms.

Although there are limitations in the research studies conducted in this area, namely that most have focused primarily on schizophrenia, this theory provides a good rationale as to why relatively low levels of substance misuse often result in negative consequences for individuals with severe mental illness.[22]


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  2. Kessler RC; McGonagle KA, Zhao S, Nelson CB, Hughes M, Eshleman S, Wittchen HU, Kendler KS (1994). "Lifetime and 12-month prevalence of DSM-III-R psychiatric disorders in the United States. Results from the National Comorbidity Survey". Archives of General Psychiatry 51 (1): 8–19. PMID 8279933.
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  7. NAMI | Dual Diagnosis - Substance Abuse and Mental Illness
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  14. Psychiatry's `bible' could roll out a whole new list of disorders - and more prescriptions for psychoactive drugs. By Sharon Kirkey, Canwest News Service, April 25, 2010
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