Abstract Objectives: Adverse Life Events (ALEs) are seen as a risk factor for both psychiatric and cognitive difficulties later in life. There is a growing interest in understanding the...Show moreAbstract Objectives: Adverse Life Events (ALEs) are seen as a risk factor for both psychiatric and cognitive difficulties later in life. There is a growing interest in understanding the relationship between ALEs and their impact on the developing individual due to the various types of consequences of ALEs (e.g., anxiety, substance use, depression, attention deficits, or language impairments). This study aimed to identify the relationship between the moment of the occurrence of ALEs (i.e., age) and intelligence (i.e., IQ) in adolescents who have experienced one or multiple ALE(s). It was hypothesized that more experiences of ALEs endured during a lifetime led to lower intelligence as experiences of ALEs lead to lower intelligence. Furthermore, it was expected that ALEs during early childhood led to lower intelligence as these experiences may result in smaller brain volume, which is associated with decreased intelligence. Additionally, experiences of ALEs during late childhood were expected to predict lower intelligence as these children tend to have a more thorough understanding of their endured ALEs. This study also examined the moderating effect of marijuana use on the relationship between age and intelligence. Here, the expectation was that individuals who reported marijuana use had lower intelligence as substance use can have a negative effect on intelligence. Methods: In total, 713 adolescents were included in this cross-sectional study design. Adolescents with a high risk to develop psychiatric disorders were oversampled for the cohort used. During this study, ALEs were assessed with the Adverse Life Events questionnaire. Intelligence was assessed with the Snijders-Oomen Non-Verbal Intelligence Test-Revised. Marijuana use was measured by using a single item of the Self-Reported Early Delinquency scale. Results: Multiple linear regressions were conducted in this study. The analyses showed that more lifetime experiences of ALEs predicted lower intelligence (partial r = -.090, p < .001). This study did not find evidence for a decrease in intelligence when experiencing ALE at a younger age. The study did find evidence that experiences of ALE at an older age predicted lower intelligence (partial r = -.088, p = .019). However, when controlling for age, gender, and socioeconomic status this effect did not remain significant (partial r = -.019, p = .607). These confounders most likely confounded the effect. No evidence was found for a stronger relationship between ALE and intelligence among marijuana users. Conclusions: In line with the expectations, more lifetime ALEs seem to negatively affect intelligence. Contradictory to the expectations, this study found that the timing of ALEs did not play a role in the relationship between ALEs and intelligence. This may be attributed to the study design where all different ALE types were combined in a total sum score and were not examined individually.Show less