Patients with substance addiction (including alcohol and drug addiction) often suffer from other mental illnesses at the same time, creating a co-morbid state. This co-morbid state is prevalent in patients with substance addiction, complicating the clinical diagnosis and treatment of addicted patients and often leading to a poor prognosis for addicted patients. Currently, in the field of substance addiction and mental health, the correct identification and rational treatment of co-morbid states have constituted an unavoidable and important challenge for clinicians. Therefore, this paper will describe the progress of the treatment of co-morbidities of substance addiction and other mental illnesses, and focus on drug treatment, but also on how to correctly identify the phenomenon of co-morbidities, and expect to be able to provide a certain reference and reference to the corresponding clinical work. 1, the concept of co-morbidity Currently, co-morbidity is usually described as co-occurring disorders, specifically referring to substance (alcohol or addictive drug) use disorders co-occurring with other mental disorders. It is specifically defined as an individual with at least one substance use disorder and at least one other mental disorder. The different diagnoses may interact with each other, but the relationship between at least one substance use disorder diagnosis and one other mental disorder diagnosis is independent of, rather than ancillary to, each other (one diagnosis may be a cluster of symptoms of the other). The diagnosis of co-morbidity, the condition, and the dysfunction caused by the co-morbidity can vary from patient to patient and from time to time within the same patient, and the conditions of substance use disorders and other mental disorders may be simultaneously less severe, more severe, or less severe for one and more severe for the other, and one or both may be in an acutely severe state or a chronically prolonged state. Co-morbidity is not a combination of particular disorders; it can contain both two or more substance use disorders and two or more other mental disorder diagnoses, and a substance use disorder can be co-morbid with any one or several other mental disorders and vice versa. Examples include heroin dependence and major depression, alcohol abuse and panic disorder, alcohol abuse and polydrug abuse and schizophrenia, and polydrug abuse and borderline personality disorder. The complexity and universality of co-morbidities Since the late 1970s, co-morbidities have been widely emphasized, and it has been found that there is a close relationship between substance addiction and depression disorders, and that co-morbidities are common and complex. It has been reported that about 50% to 70% of addicted patients suffer from other mental illnesses, and about 20% to 50% of patients with other mental illnesses suffer from co-morbidities. About 47% of patients with schizophrenia and 61% of patients with bipolar disorder have co-morbid substance addictions, respectively. Co-occurring disorders have a poor outcome and prognosis and often lead to relapse, AIDS infection, and suicide. Recent surveys show that in the United States, the annual prevalence of co-occurring substance addictions and other serious mental illnesses exceeds at least 5.2 million, of which only 8.5 percent are treated appropriately. In China, about 2/3 of the heroin addiction patients and other mental diseases co-morbidities, of which about 20% co-occur with depressive disorders, co-occur with antisocial personality accounted for about 40%. 3, the identification of co-morbidities The correct identification of co-morbidities is the basis for rational treatment. Clinically, how to identify co-morbidities and distinguish whether the mental symptoms of addicted patients are caused by addictive substances or independent of other mental illnesses is also a difficult point. According to the criteria of the fourth edition of the U.S. Diagnostic Manual of Mental Disorders, mental and emotional symptoms that occur during intoxication or withdrawal from addictive substances and within one month of intoxication or withdrawal are often caused by addictive substances and are not diagnosed as co-morbidities. However, if a patient exhibits severe mental and emotional symptoms during abuse or after withdrawal that are well beyond what the addictive substance could have caused in the appropriate dosage and duration, these mental and emotional symptoms may be caused by other independent psychiatric disorders and need to be considered for a diagnosis of co-morbidity. Appropriate screening and diagnostic scales can be selected to assist in the clinical identification of co-morbidities, and appropriate professional training should be provided before using the scales. In China, screening scales can be selected from the Brief International Neuropsychiatric Interview (M.I.N.I.) and the Brief Symptom Inventory-18 (BSI-18). Diagnostic scales can form a clear diagnosis and collect more detailed and comprehensive information, but the professional qualification requirements of diagnostic scales are high and time-consuming, and they are mostly used in clinical research. Currently, the authoritative diagnostic scales include the Clinical Scale for Neuropsychiatry (SCAN), the Composite International Diagnostic Inventory (CIDI), and the DSM-IV Clinical Interview (SCID). It is worth noting that the diagnosis of co-morbidity requires a continuous observation process, which cannot be assessed only by a single scale at a time, but also by repeated diagnosis, if necessary, to avoid and minimize the influence of addictive substances on the diagnostic results as much as possible. Treatment of co-morbidities The treatment of co-morbidities should be integrated, including both the treatment of substance addiction and the treatment of other mental illnesses. Treatment measures such as psychotherapy, medication, crisis intervention, rehabilitation and social support can be integrated into the integrated treatment. Integrated treatment involves medical, psychological, social, and cultural domains, and for clinical reasons, this article focuses on the pharmacological aspects of co-morbidities. Before treating co-morbidities with medication, the toxicity, tolerance and addictiveness of the medication itself should be carefully considered. In principle, non-pharmacologic treatments are preferred first. When the efficacy of non-pharmacological treatment is unsatisfactory, then non-psychoactive drugs should be considered for pharmacological treatment. For example, antidepressants, antipsychotics, lithium salts and non-benzodiazepine anxiolytics such as buspirone. When the efficacy of both non-pharmacological and non-psychoactive medications is unsatisfactory, the last consideration is to choose pharmacological treatment with psychoactive medications such as benzodiazepines, opioids, and stimulants. It is important to note that the relationship between the various treatment measures is complementary, such as psychotherapy and other non-pharmacological measures can not be effective in alleviating the symptoms of depression, the addition of antidepressants can be supplemented, rather than the use of antidepressants to replace the psychotherapy and so on. Different co-occurring psychiatric disorders in addicts require different therapeutic medications, which need to be categorized and introduced. Pharmacotherapy for co-occurring mental disorders: Early studies have shown that promethazine and desipramine are effective in treating the co-occurring disorders of alcohol dependence and depression, reducing depressive symptoms and prolonging alcohol withdrawal, and that lithium is effective in the co-occurring disorders of substance addiction and bi-directional affective disorder, reducing the misuse of alcohol and addictive drugs, as well as improving the patient’s social functioning. A controlled study of valproate, lithium, benzodiazepines, nerve blockers, and tricyclic antidepressants showed that patients with substance addiction and bipolar disorder co-morbidities had the best adherence to valproate, lithium had poor adherence due to side effects, and benzodiazepines, nerve blockers, and tricyclic antidepressants were often overused. It has also been shown that valproate significantly improves mood, reduces cravings, and prolongs withdrawal in the treatment of co-occurring substance addiction and affective disorders, and that valproate can be safely combined with its medications. Pharmacotherapy for co-occurring anxiety disorders: for co-occurring substance addiction and anxiety disorders, there are different medication choices for different types of anxiety disorders. Fluoxetine, paroxetine and other selective 5-hydroxytryptamine reuptake inhibitors have fewer side effects, good efficacy, and can be commonly used in patients with co-morbidities of various anxiety disorders. Non-benzodiazepine anxiolytics such as buspirone are non-addictive and are suitable for substance addicts with co-morbid generalized anxiety, and can significantly improve anxiety symptoms and reduce the amount of substance abuse, and can be used as the drug of choice. Venlafaxine is also effective in treating substance addicts who co-occur with generalized anxiety. Benzodiazepines can be used in acute episodes of panic disorder and are also effective in post-traumatic stress disorder, but benzodiazepines are addictive and are only suitable for short-term application in restricted doses. Tricyclic antidepressants can also be used to treat substance addicts with co-occurring panic disorder or generalized anxiety, but tricyclics have relatively significant side effects, may increase the cardiotoxicity of addictive substances, and must be used with caution. Medication for co-occurring schizophrenia: Atypical antipsychotics such as olanzapine and clozapine are effective in the co-morbidity of substance addiction and schizophrenia. This class of drugs may have a role in treating schizophrenia along with reducing substance abuse, possibly through effects on the central pentazocine system. Recent studies have shown that olanzapine not only significantly reduces psychotic symptoms in co-morbid patients compared to haloperidol, but also enhances treatment adherence and reduces abuse of addictive substances. Pharmacological treatment for co-occurring personality disorders: A recent study reported that compared with the application of fluoxetine and paroxetine combined with clonidine, the application of olanzapine has a significant efficacy in the aggressive personality associated with heroin-dependent patients, which can reduce the patients’ aggressive language and aggressive/hostile behaviors, and reduce the occurrence of aggressive events. Currently there are few reports of pharmacological treatments for co-morbidities of substance addiction and personality disorders, which may be related to the fact that non-pharmacological treatment measures are more often used for personality disorders. The above discussion focuses on the pharmacological treatment of co-morbidities between substance addiction and other psychiatric disorders, and also describes how to recognize co-morbidities, which is expected to provide a reference for the corresponding clinical work.