Background: A number of serious cardiovascular safety concerns related to the use of atypical antipsychotics, compared with no use, have emerged, but nearly all reports are from studies of older patients. We aimed to compare the risk of cardiovascular events between the three most commonly used atypical antipsychotics in young and middle-aged adults.

Methods: We conducted a nationwide register-based cohort study in Denmark, 1997-2011, including adults aged 18-64 years, who started treatment with oral or intramuscular olanzapine (n = 15,774), oral quetiapine (n = 18,717), and oral or intramuscular risperidone (n = 14,134). The primary outcome was any major cardiovascular event (composite of cardiovascular mortality, acute coronary syndrome, or ischemic stroke) within 1 year following treatment initiation. Cox regression was used to estimate hazard ratios (HRs) while on current antipsychotic monotherapy in the outpatient setting, adjusting for an outcome-specific disease risk score.

Results: The crude rate of any major cardiovascular event was 5.3 per 1,000 person-years among olanzapine users, 3.4 in quetiapine users, and 5.2 in risperidone users. Compared with risperidone, the risk of any major cardiovascular event was not significantly different in olanzapine users (HR 0.90, 95 % confidence interval [CI] 0.53-1.52) and quetiapine users (HR 0.79, 95 % CI 0.45-1.39). The absolute risk difference per 1,000 person-years on treatment was -0.5 (95 % CI -2.4 to 2.7) events for olanzapine and -1.1 (95 % CI -2.9 to 2.0) events for quetiapine.

Conclusions: Among young and middle-aged outpatients, the risk of acute major cardiovascular events was similar with use of olanzapine, quetiapine, and risperidone. Although moderate relative differences cannot be ruled out, any differences are small in absolute terms.