Intervention in the early-stages of psychosis may be able to shape the clinical course; critical period (CP) is best represented by the first 5 years from first admission (FA).

To investigate the effectiveness of pharmacological intervention within and beyond the CP.

(1) To compare hospitalization rates of patients stabilized on treatment with LAIs and CLZ. (2) To determine whether treatment with LAIs and CLZ within CP can influence hospitalization rates.

Data were retrospectively collected from patients diagnosed with non-affective psychoses with FA between 2000 and 2014; 200 patients were then divided into three groups, according to stabilized treatment regimen during the final year of observation: treatment as usual (TAU), CLZ, LAIs. hospitalization duration (HSPD) and frequency (HSP) were calculated for each group.

Despite a major severity before assignment to either CLZ or LAIs treatment, HSPD and HSP in both groups shifted below those observed for the TAU arm. Patients who began treatment with LAIs within the CP showed a highly significant decrease of both HSPD and HSP (respectively 17.4 ± 18 vs. 2.6 ± 8.2; Z = −2.856; P < 0.005 and 1.1 ± 0.8 vs. 0.2 ± 0.5; Z = −3.115; P < 0.005). No significant changes in hospitalization rates were observed for subjects who began treatment with LAIs after the CP.

Our study confirms that treatment with either CLZ or LAIs significantly impacts the course of psychotic disorders. The data seem to suggest that LAIs and CLZ should be considered more effective than conventional oral antipsychotics in the early-stages of psychotic illness. The difference among treatments tends to wane beyond the CP, especially for LAIs.

The authors have not supplied their declaration of competing interest.