Objective:
We aimed to assess the predictive associations of age at first drink (AFD), age at first intoxication (AFI), frequency of intoxication, and self-reported alcohol tolerance at ages 15–16 with self-harm requiring medical attention or suicide death by age 33.

Method:
In an ongoing follow-up study, the Northern Finland Birth Cohort 1986, a total of 7,735 individuals were included at ages 15–16. Information on alcohol and other substance use was assessed via questionnaires. Information on self-harm or suicide was collected from national registers until the participants were 33 years of age. Baseline psychiatric symptomatology measured with the Youth Self-Report questionnaire and sociodemographic background variables were controlled for in multivariable analyses using Cox regression analyses.

Results:
Male gender and psychiatric symptoms at ages 15–16 were consistently associated with greater risk of self-harm and suicide death. When baseline psychiatric symptomatology and other background variables were adjusted for, younger AFI (hazard ratio [HR] = 2.28, 95% CI [1.16, 4.47]) and high inherent alcohol tolerance (HR = 3.76, 95% CI [1.55, 9.08]) were associated with self-harm. Furthermore, frequent alcohol intoxication (HR = 5.39, 95% CI [1.44, 20.23]) and high inherent alcohol tolerance (HR = 6.20, 95% CI [1.18, 32.45]) were associated with suicide death by age 33.

Conclusions:
High alcohol tolerance, age at onset of intoxication, and frequency of alcohol intoxication in adolescence appear to be significant predictors of self-harm and suicide in early adulthood. Self-reported alcohol tolerance in adolescence is a novel empirical approach to assess adolescent alcohol use associating with subsequent harms.