Inattentive ADHD: Causes and symptoms

Understanding the root causes of inattentive ADHD can help reduce the stigma surrounding it and help recognise the symptoms, which can help you get a diagnosis.

It can also be useful for parents and teachers to understand why someone with inattentive ADHD acts the way they do.

What causes inattentive ADHD?

There’s no one single cause of ADHD; it has a strong genetic component, with environmental factors also playing a role.

Genetics

ADHD is a highly heritable condition. This means around 74% of it can be explained by genetics, while the remaining 26% is linked to environmental factors.^[1]

Genes are the things that carry your DNA, and they shape who you are and what you do. Some gene variations, such as the DAT1 and DRD4 genes, have been associated with ADHD. They are responsible for how dopamine is used – a neurotransmitter that helps you focus and concentrate. Dysregulation of dopamine is associated with ADHD.

Research shows that if one parent has ADHD, the chance of their child having it increases significantly. But this doesn't mean that every parent with ADHD will have a child with ADHD. Studies show that the incidence of ADHD with a mother who has the condition is 41.3%, while for fathers with ADHD, it is 51%.^[2]

Brain chemistry

Although other neurotransmitters can also play a role, two key ones involved in ADHD are: dopamine and norepinephrine.

Dopamine regulates your attention, focus, motivation, and reward. It helps you get started on a task, and makes you feel a sense of achievement when you complete it.

Norepinephrine has a similar role; it increases alertness, focus, and influences your mood. It plays a key role in your sleep cycle, helping you stay awake during the day and keep you focused throughout. Low levels of norepinephrine have also been linked to depression and anxiety.^[3]

But people with ADHD typically have lower levels of both dopamine and norepinephrine, which can lead to challenges like:

• Difficulty focusing on tasks, even simple ones
• Struggling to fall and stay asleep
• Lacking motivation or feeling ambitionless
• Zoning out without realising

What are the symptoms of inattentive ADHD?

Inattentive ADHD doesn't present the same way as hyperactive ADHD or even combined ADHD. Symptoms of inattentive ADHD may include:

1. Difficulty focusing or paying attention

Your mind may wander during lessons or meetings. When talking to a friend, you might “zone out” in the middle of the conversation or find it hard to listen and fully understand what they’re saying.

2. Trouble completing tasks

You may struggle to find the motivation to start tasks such as homework or chores. Even when you begin, it can be hard to follow through to the end because you get distracted or lose concentration – especially with tasks that feel repetitive or boring.

3. Mental fatigue

Trying to keep up, fit in, and meet deadlines can feel overwhelming. For example, you might know you have a project due soon, but still find it hard to start. This can make you feel restless, stressed, or mentally exhausted.

4. Emotional sensitivity

When you feel overwhelmed or stressed, small things may trigger stronger emotional reactions. You might become irritated more easily or cry more often than others in similar situations.

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Overview

Read next:

Diagnosis & treatment

References:

1. Faraone, S. V., & Larsson, H. (2018). Genetics of attention deficit hyperactivity disorder. Molecular Psychiatry, 24(4), 562.
2. Starck, M., Grünwald, J., & Schlarb, A. A. (2016). Occurrence of ADHD in parents of ADHD children in a clinical sample. Neuropsychiatric Disease and Treatment, 12, 581.
3. Paris Brain Institute. (2025). Noradrenaline (or norepinephrine) | Paris Brain Institute.