Risk of suicide after a self-poisoning episode: a self-controlled case series study.

Abstract

The risk of death from suicide after self-poisoning has been known to be significantly higher as compared to the general population. Nevertheless, the change in suicide risk before and after self-poisoning is still unclear. The database of territory-wide medical records collected by the Hospital Authority of Hong Kong was used to identify inpatients who have survived the first-ever self-poisoning but died by suicide between January 1, 2001, and December 31, 2010. A self-controlled case series ("SCCS") design controlling for time-invariant patient confounders was used to explore the temporal change in suicide risk after the first self-poisoning episode. During the study period, 227 people in the database died from suicide after surviving one episode of self-poisoning. A significant increase of the risk of suicide in the first 12months after the first lifetime self-poisoning-Risk Ratio ("RR") 2.88 (95% CI 1.74-4.76)-was detected. The RR gradually returned to baseline levels after the second post-poisoning period. By within-person comparison, the net increase of the suicide risk caused by the first self-poisoning was quantitatively modeled, demonstrating that the first lifetime self-poisoning event itself is a modifiable risk factor of subsequent suicide death.