Background: Suicidal thoughts and non-suicidal self-harm are common in young people and are strongly associated with suicide attempts. This longitudinal study aimed to identify predictors of future suicide attempts within these high-risk groups.

Methods: Participants were from the Avon Longitudinal Study of Parents and Children (ALSPAC), a population-based birth cohort study in the UK. The sample included 456 young people who reported suicidal thoughts and 569 who reported non-suicidal self-harm at age 16 years. Logistic regression analyses were used to explore associations between a wide range of prospectively recorded risk factors and future suicide attempts, assessed at age 21 years.

Outcomes: The proportion of adolescents who went on to make a suicide attempt was the same in both groups (12%). Amongst those with suicidal thoughts, the strongest predictors of transition to attempts were: non-suicidal self-harm (OR=2.78); cannabis (OR=2.61) and illicit drug use (OR=2.47); exposure to self-harm (family OR=2.03; friend OR=1.85), and higher levels of the personality type ‘Intellect/openness’ (OR=1.62). Amongst those with non-suicidal self-harm at baseline, the strongest predictors were: cannabis (OR=2.14) and illicit drug use (OR=2.17); sleep problems (waking in the night OR=1.91; insufficient sleep OR=1.97), and lower levels of the personality type ‘extraversion’ (OR=0.71).

Interpretation: Most adolescents who think about suicide or engage in non-suicidal self-harm will not make an attempt on their life. Many commonly cited risk factors were not associated with transition to suicide attempt among these high-risk adolescents. Our findings suggest that asking about substance use, non-suicidal self-harm, sleep, personality traits, and exposure to self-harm could inform risk assessments, and may help clinicians to identify which young people are at greatest risk of attempting suicide in the future.

Funding: American Foundation for Suicide Prevention; NIHR Biomedical Research Centre at the University Hospitals Bristol NHS Foundation Trust and the University of Bristol.

Keywords: Suicide attempt; ideation; suicidal thoughts; ALSPAC; longitudinal