How and why does ADHD lead to depression in young people?

Depression is a common mental health condition that typically develops during adolescence or young adulthood. Young people with attention deficit/hyperactivity disorder (ADHD) are around five-times more likely to experience depression than those without. Depression in those with ADHD is especially serious - for example, with a higher risk of suicide compared to either ADHD or depression alone. However, the typical interventions for depression do not appear to be as effective for young people with ADHD. To better help these young people, we first need to understand how and why ADHD can lead to depression.
This project will use two large existing datasets from the UK general population. These contain detailed information collected across childhood, adolescence and young adulthood, including measures of ADHD, depression, and factors that may link the two. We will use advanced statistical methods on these datasets to help understand:
- How and why ADHD can lead to depression.
- How links between ADHD and depression change from childhood, to adolescence, and into young adulthood.
The project has four main aims.
First, I will examine how the link between ADHD and depression symptoms develops across childhood, adolescence and young adulthood. I will look at whether depression starts earlier or lasts longer for young people with ADHD, and whether this is different depending on when ADHD starts and how long ADHD lasts. I will also look at whether different types of depression symptoms are associated with ADHD at different ages.
Second, to help inform future potential targets for depression interventions for young people with ADHD, I will examine whether characteristics that relate to how people think and learn (e.g. problems relating to impulsivity, how individuals think about negative events) and factors relating to emotions or behaviours (irritability and anxiety) are important links between ADHD and depression.
Third, because some therapies for depression in young people aim to improve their relationships with friends and families, I will examine the extent to which relationship problems with parents, friends and romantic partners contribute to the link between ADHD and depression across childhood, adolescence and young adulthood.
Finally, I will examine the relative contributions of genes and environment to the link between ADHD and depression. I will then test whether the associations between ADHD, depression and the identified factors that link these are driven by genes, or if they might cause depression in young people with ADHD. This is important because if they cause depression, then targeting these factors in interventions may be more likely to reduce depression.

Depression is the leading mental health contributor to the Global Burden of Disease and its prevalence has increased sharply in young people in recent years. An especially pertinent risk pathway into early depression is ADHD, and depression in those with ADHD is associated with even greater impairment and poorer outcomes compared to either condition alone.
This project will generate much needed evidence on how ADHD and depression symptoms co-develop over time, the role of cognitive, clinical and interpersonal mechanisms, and the contribution of genetics. This is important to investigate because standard interventions for depression appear to be less effective for young people with ADHD.
Key research questions are:
1) How do ADHD and depression co-develop over time?
2) Which cognitive and clinical mechanisms link ADHD and depression, and when?
3) Which interpersonal relationships contribute to the link between ADHD and depression, and when?
4) What are the relative genetic contributions to the overlap between ADHD, depression and identified cognitive, clinical and interpersonal mediators?
This project will use advanced longitudinal statistical methods and a developmental approach to generate needed evidence on how and why ADHD leads to depression in young people. I will leverage data from two UK population cohorts with rich data spanning childhood, adolescence and young adulthood.
The project will continue to involve young people with lived experience, who will play a vital role in the dissemination process and ensure outputs are engaging, meaningful and accessible for all audiences, especially young people and families.