Risk of suicide following deliberate self-poisoning

Importance — Suicide is the 10^th leading cause of death in the United States and its rate has risen by 16% in the past decade. Deliberate self-poisoning is the leading method of attempted suicide. Unlike more violent methods, which are almost universally fatal, survival following self-poisoning is common, providing an opportunity for secondary prevention. However, the long-term risk of suicide following a first episode of self-poisoning is unknown.

Objective — To determine the risk of suicide and mortality from other causes following a first self-poisoning episode.

Design — Population-based cohort study using multiple linked healthcare databases.

Setting — Ontario, Canada from April 2002 to March 2011.

Participants — The researchers identified all individuals with a first self-poisoning episode. For each individual with a deliberate self-poisoning, the researchers randomly selected one control from the same population with no such history, matched on age (within 3 months), sex and calendar year.

Main Outcomes — The primary analysis examined the risk of suicide following discharge after self-poisoning. Secondary analyses explored factors associated with suicide and examined the risk of death from accidents and death from any cause.

Results — The researchers identified 65,784 patients (including 18,482 [28.1%] younger than 20 years) discharged after a first self-poisoning episode. Over a median follow-up of 5.3 years, 4,176 died, including 976 (23.4%) deaths from suicide. The risk of suicide following self-poisoning was markedly increased relative to controls (adjusted hazard ratio 42.0; 95% confidence interval 27.8 to 63.4), corresponding to a suicide rate of 280 vs. 10 per 100,000 person-years, respectively. The median time from hospital discharge to suicide was 585 days (inter-quartile range 147 to 1,301). Older age, male sex, multiple intervening self-poisoning episodes, higher socioeconomic status, depression and recent psychiatric care were strongly associated with suicide. Patients with self-poisoning were also more likely to die from accidents (adjusted hazard ratio 10.5; 95% confidence interval 8.1 to 13.5) and all causes combined (adjusted hazard ratio 5.6; 95% confidence interval 5.1 to 6.0).

Conclusions and Relevance — A first self-poisoning episode is a strong predictor of subsequent suicide and premature death. Most suicides occur long after the index poisoning, emphasizing the importance of longitudinal, sustained secondary prevention initiatives.