Objective: Substance use disorders are highly prevalent in people living with a mental health disorder. Co-occurring substance use disorders have been associated with a worse prognosis and poorer adherence to treatment. The aim of this study was to analyze the temporal trends in the prevalence of substance use disorders in patients admitted to a psychiatric inpatient unit between 1998 and 2020.
Methods: This is a retrospective study based on the registry of 18,367 hospitalizations and 7,124 patients with a mental health disorder admitted during the period 1998 to 2020 in Malaga, Spain. Time trend analysis by gender and substance used was calculated using a segmented regression model. The permutation test was used to determine inflection points. A sensitivity analysis was performed based on the assumptions of autocorrelation and homoscedasticity.
Results: A total of 22.2% of admissions had a diagnosis of mental health disorder and co-occurring substance use disorders. Prevalence was higher among males (30.0%) than females (9.4%; p < .001). Patients with both disorders had a shorter length of stay by 2 days (p < .001) and a younger age at first admission (by 6.5 years; p < .001) compared to patients without substance use disorders. There was no difference in the total number of hospitalizations between the two groups. Psychotic disorders and multiple drug use disorders were the most prevalent diagnoses in men compared to women, whereas personality disorders and alcohol use were the most common diagnoses in women. We observed an increase in the prevalence of dual diagnosis between 2005 and 2020. There was a 3.0% increase in cannabis-related admissions per year during the whole study period (p < .001). Cannabis and cocaine use disorders have become the most prevalent in the last 10 years, while opioid and alcohol use disorders have decreased.
Conclusions: Co-occurring substance use disorders are highly prevalent among hospitalized patients. In recent years, the pattern of substance use has shifted, with cannabis being the most prevalent, while opiates and alcohol substance use have decreased. We need to devise a specialized approach and integrative treatment for patients with co-occurring disorders.
Keywords: Dual diagnosis; comorbidity; gender differences; hospitalization; substance use disorder.