Is there an association between selective serotonin reuptake inhibitors and risk of abnormal bleeding ? Results from a cohort study based on prescription event monitoring in England

To investigate whether an association between the use of selective serotonin reuptake inhibitor (SSRI) antidepressants and abnormal bleeding is demonstrated in a large population study. An observational cohort study using cohorts from the Drug Safety Research Unit's prescription event monitoring database was performed. Analysis of combined haemorrhagic event rates calculated for the first 6 months of treatment for four SSRIs showed no significant difference between the rate for abnormal bleeding in the first month after starting treatment compared with months 2-6 [difference in rates 0.63 per 1000 patient months of treatment, 99% confidence interval (CI) -0.4, 1.67]. Comparison of the rates for the exposed combined SSRI cohort with the unexposed non-psychiatric drug cohort for the first month [relative risk (RR) 1.38, 95% CI 0.82, 2.34] and months 2-6 (RR 1.17, 95% CI 0.81, 1.68) showed no significant differences after adjustment for age and gender. However, there was a tendency towards highest risk with the combined SSRI cohort and lowest with the baseline cohort. This study provides weak evidence to support the hypothesis of a link between SSRIs and precipitation of bleeding events at a population level. The 95% CI is consistent with a possible risk of bleeding associated with SSRI users versus non-psychiatric drug users in the first month. Fuller consideration of confounding would be possible using follow-up of identified cases in a nested case-control study.