Background <p>Gender differences in psychiatric symptoms and pharmacological treatment are well-documented in general psychiatry but remain understudied in forensic psychiatric populations. This study aimed to explore gender-based differences in sociodemographic, clinical, criminal, biochemical, and pharmacological characteristics among forensic inpatients with serious mental illness (SMI).</p> Methods <p>A total of 100 patients (59 men, 41 women) with SMI who were admitted to the forensic psychiatry department by court order were included in a two-time-point observational cohort study with assessments at admission (T1) and discharge (T2). Sociodemographic and clinical traits, criminal data, psychopathological features, blood test results, medication dosages (including antipsychotic equivalent doses calculated using four methods), and treatment side effects were evaluated (T1 and T2) and then compared between genders.</p> Results <p>No gender differences were observed in clinical symptom severity, functional level, side-effect profile, hospitalization duration, or treatment type (monotherapy vs polypharmacy; LAI use; adjunctive medications such as benzodiazepines, mood stabilizers, and anticholinergics). Men experienced more hospital admissions and guardianship cases. The age at first offense was younger among men, but the rate of violent crime was higher among women. Men were prescribed notably higher doses of antipsychotics, even when accounting for confounders (according to the WHO-defined daily dose and the Maudsley 2025 equivalent dose table). Furthermore, men were more likely to be using high doses of antipsychotics.</p> Conclusions <p>The study provides new data from an underrepresented population. It highlights gender differences in forensic psychiatry, especially in treatment dosages. Clinicians view male patients with SMI as more aggressive, impulsive, or more likely to reoffend. More personalized and gender-sensitive prescribing practices may be necessary in forensic psychiatry settings.</p>