Incident low-dose quetiapine use in adults newly diagnosed with depression in primary care: A nationwide register-based study.

AIMS: This study aimed to investigate the incidence of low-dose quetiapine initiation and associated factors in adults newly diagnosed with depression in primary care. METHODS: We obtained medication dispensing records, primary and secondary care diagnoses and employment status for antipsychotic-naïve individuals aged 16-65 newly diagnosed with depression in primary healthcare from several national Finnish registers in 2016-2022. We then calculated the incidence of low-dose (≤50 mg) quetiapine initiation from 2 years before to 2 years after the depression diagnosis. Modified Poisson regression models derived adjusted risk ratios (aRRs) and 95% confidence intervals (CIs), assessing the association between covariates and low-dose quetiapine initiation. RESULTS: Of the 189 115 individuals with depression, 13.4% (25 373) initiated low-dose. The incidence of low-dose quetiapine peaked in the first 30 days following the depression diagnosis, constituting 14.8% of all initiations. Initiation had the strongest association with younger age (16-24 vs. 55-65 years: aRR 1.87, 95%CI 1.80-1.96) and psychiatric comorbidities, especially alcohol use disorder (1.44, 1.39-1.50) and other substance use disorders (1.27, 1.19-1.36). Ischaemic heart diseases had a positive association (1.13, 1.04-1.22), while hyperlipidaemia had a negative association (0.91, 0.86-0.97); other cardiometabolic conditions had no significant associations. Among other medications assessed, SSRI and hypnotic antidepressant use had the strongest associations with low-dose quetiapine initiation (1.81, 1.77-1.86 and 1.81, 1.77-1.85, respectively). CONCLUSIONS: Low-dose quetiapine initiation is common among adults newly diagnosed with depression in primary care. The benefits of this practice should be weighed against cardiometabolic and other adverse effects.