Study Design This study was designed as a comparative, cross-sectional case-control study examining the effect of comorbid alcohol and substance use disorder (ASUD) on clinical course and social inclusion among individuals with severe mental illness followed at a Community Mental Health Center (CMHC). The study did not involve any interventions.

Aim The aim of this study is to examine the effect of comorbid alcohol and substance use on clinical course parameters-such as number of hospitalizations and medication dosages-and on social inclusion indicators-such as employment, social participation, and social adjustment-among individuals with severe mental illness followed at the CMHC, in comparison with a matched control group without substance use.

Research Questions

What are the rates of comorbid alcohol and substance use among patients with severe mental illness followed at the CMHC? What are the current addiction symptoms, number of hospitalizations, and employment rates among individuals with severe mental illness and comorbid ASUD? What is the level of continuity of CMHC engagement and social participation among individuals with severe mental illness and comorbid ASUD, and what factors influence it? How does the level of social inclusion among individuals with severe mental illness and comorbid ASUD compare with that of individuals without ASUD?

Hypotheses

H1: The average annual number of hospitalizations among individuals with a dual diagnosis (severe mental illness + ASUD) followed at the CMHC is significantly higher than among those without substance use.

H2: Among individuals with a dual diagnosis, the daily medication doses (e.g., chlorpromazine equivalents) required to control psychotic or manic symptoms are higher than in the control group.

H3: Social inclusion is lower among patients with substance use compared with the control group.

H4: Employment rates among individuals with a dual diagnosis are significantly lower than among those with severe mental illness alone.

H5: Substance use negatively affects patients' social participation, including involvement in activities and friendships.

H6: Attendance rates at CMHC workshops and rehabilitation programs are lower among individuals with substance use compared with the control group.

Study Setting and Sample The study will be conducted at the Bolu İzzet Baysal Mental Health and Diseases Rehabilitation Center , which has a follow-up pool of approximately 1,300 active patients. The study population consists of these 1,300 individuals. The sample size was calculated using Cochran's formula with finite population correction, at a 95% confidence level and a 5% margin of error. This calculation yielded a minimum sample size of 297 individuals. Case and control groups will be distributed in an approximately 1:1 ratio (148 cases, 149 controls).

Data Collection Form

1. Sociodemographic Variables Age, gender, marital status, education level, living arrangement (living with family/alone/in an institution, etc.), employment status (employed, unemployed, retired, or receiving a disability pension), and social security status.

2. Clinical Variables

   Primary psychiatric diagnosis (per DSM-5: schizophrenia spectrum disorders or bipolar disorder) ASUD diagnosis and type of substance used (alcohol, cannabis, stimulants, etc.) Duration of illness (in years) Length of follow-up at the Rehabilitation and Treatment Center (in months) Number of psychiatric hospital admissions and total days of hospitalization over the past 2 years Calculated daily chlorpromazine-equivalent (CPZ-eq) dose of antipsychotic and mood-stabilizing medications used Treatment adherence, assessed based on prescription refill frequency and clinical follow-up notes Substance use will be assessed using the Drug Abuse Screening Test (DAST-10) and alcohol use using the Alcohol Use Disorders Identification Test (AUDIT)

3. Social Inclusion and Rehabilitation Variables

   Attendance rate at TRSM workshops and rehabilitation programs (number of sessions attended / number of sessions planned) Indicators of social adjustment: employment status, independent living skills, and breadth of social network (relationships outside the family) Number of emergency department visits over the past 12 months Social Exclusion (Ostracism) Scale score

4. Drug Abuse Screening Test (DAST-10) The DAST-10 is a 10-item self-report instrument developed to screen for problems related to the use of substances other than alcohol and tobacco. Developed by Harvey A. Skinner, it assesses substance-related problems over the past 12 months. Items are answered yes/no, with each "yes" scored as 1 point (item 3 is reverse-scored). Total scores range from 0 to 10, with higher scores indicating more severe substance use problems. A Turkish validity and reliability study found an internal consistency coefficient of Cronbach's α = 0.92. That study recommended a cutoff score of ≥4, yielding a sensitivity of 0.98 and specificity of 0.91. The scale is widely used to rapidly screen for substance use problems in clinical and research settings.

5. Alcohol Use Disorders Identification Test (AUDIT) The AUDIT is a screening instrument developed to identify hazardous and harmful alcohol use. It was developed by Thomas F. Babor and colleagues as part of a multicenter study conducted by the World Health Organization (WHO). The AUDIT consists of 10 items assessing frequency of alcohol use, symptoms of dependence, and alcohol-related problems over the past 12 months. Items are scored on a 0-4 Likert-type scale, yielding a total score range of 0-40, with higher scores indicating more hazardous drinking. A Turkish validity and reliability study confirmed the Turkish version as a valid and reliable measurement tool; a cutoff score of 8 or above is generally accepted to indicate hazardous/harmful alcohol use. The AUDIT is widely used in clinical and research settings for rapid, effective screening of alcohol-related risk. The scale's total possible score is 40, with a cutoff of 8, and its reliability coefficient is 0.65.

6. Social Exclusion (Ostracism) Scale This is a brief self-report scale developed to assess the frequency of social exclusion (ostracism) experiences in individuals' daily lives. Developed by Sandra C. Rudert and colleagues, it measures exclusion experiences over the preceding two months. The scale consists of 4 items with a unidimensional structure, rated on a 7-point Likert scale (1 = Never, 7 = Always). The total score is calculated by summing item scores, with higher scores indicating more frequent experiences of social exclusion. Confirmatory factor analysis supported a single-factor structure with good model fit (CFI = 0.99, RMSEA = 0.04), and internal consistency was high (Cronbach's α = .90), confirming the scale as a reliable measurement tool.

Inclusion Criteria:

• Being 18 years of age or older,
• Having a diagnosis of Schizophrenia Spectrum Disorder and Other Psychotic Disorders or Bipolar Disorder according to DSM-5 diagnostic criteria,
• Being actively followed up at the TRSM for at least 6 months.

Exclusion Criteria:

• Individuals diagnosed with organic brain damage or neurodevelopmental disorders (intellectual disability, etc.),
• Individuals with severe cognitive impairment that prevents them from communicating adequately.

Adults with alcohol and substance use disorders among individuals with severe mental illness who are being followed up at the Community Mental Health Center.