Diurnal variation in antipsychotic-associated acute dystonia: A retrospective cohort study

Acute dystonia is a distressing adverse effect of antipsychotics. A circadian pattern has been suggested, but evidence is limited.

To investigate whether antipsychotic-induced acute dystonia shows a time-of-day distribution.

We conducted a retrospective review of patients admitted to a first-episode psychosis ward (2017-2025). The timing of dystonia onset was extracted from clinical records. Temporal clustering was assessed using circular statistics (Rayleigh test) and Chi-square analyses of predefined time blocks.

Thirty-five cases of acute dystonia were identified (mean age 22.4 years, SD 4.1; 71.4% male). Events clustered in the afternoon and early evening (mean time 5:12 p.m.; Rayleigh R = 0.71, p < 0.001). Chi-square tests confirmed deviation from uniformity (p < 0.001). Sensitivity analyses showed that results were independent of antipsychotic dosing time, time to reaction, and antipsychotic dose.

Acute dystonia onset appeared to cluster in the late afternoon and early evening, warranting further investigation of time-of-day effects in monitoring antipsychotic-related motor effects.