Table 1 Pre-specified research questions and hypotheses in this Registered Report

To what extent is age at menarche associated with adolescent depression?

We hypothesised that earlier age at menarche would be associated with elevated depressive symptoms at age 14 (H1a)

We hypothesised that earlier age at menarche would be associated with higher rates of depression diagnoses during adolescence (H1b)

Does age at menarche associate with symptoms or diagnoses in other domains of mental health (anxiety, CD, ODD, or ADHD), independent of depression?

We hypothesised that age at menarche would be associated with symptoms in other domains at age 14, independent of depressive symptoms (H2.1–4a)

We hypothesised that age at menarche would be associated with diagnoses in other domains in adolescence, independent of depressive disorders (H2.1–3b)

What is the evidence for a causal link between age at menarche and depression?

We hypothesised that earlier age at menarche would show a causal relationship, resulting in elevated depressive symptoms at age 14 (H3a)

We hypothesised that earlier age at menarche would show a causal relationship, resulting in higher rates of depression diagnoses during adolescence (H3b)

Is there evidence of causal links between age at menarche and other domains of mental health?

We hypothesised that age at menarche would show a causal relationship with symptoms in other domains (H4.1–4a)

We hypothesised that age at menarche would show a causal relationship with rates of diagnoses in other domains (H4.1–3b)