What is ADHD? A plain-English guide for adults

What ADHD is, how it shows up in reading and everyday work, and how adults get assessed. Plain language, with sources.

ADHD, short for attention deficit hyperactivity disorder, is a condition that affects how the brain manages attention, activity and impulses. It starts in childhood, it often carries on into adult life, and it is common. A 2021 review in the Journal of Global Health estimated that about 2.6% of adults worldwide have ADHD that began in childhood and persisted (Song et al., 2021). This guide explains what ADHD is, how it shows up in reading and everyday work, and how adults get assessed, with a source for each health claim.

Key Takeaways

What is ADHD?

ADHD is a neurodevelopmental condition marked by an ongoing pattern of inattention, hyperactivity and impulsivity that gets in the way of daily life, according to the US National Institute of Mental Health (NIMH). Inattention means finding it hard to stay on task, follow through and stay organized. Hyperactivity means moving or talking more than the moment calls for, or, in adults, feeling restless inside. Impulsivity means acting before thinking it through, interrupting, or finding it hard to wait.

Clinicians describe three presentations, depending on which signs are strongest: mainly inattentive, mainly hyperactive-impulsive, or combined (CDC). The presentation can change over a lifetime, which is one reason adults who were never the restless child in class are sometimes surprised to learn they have ADHD.

What causes ADHD?

Genes play the largest known part. A review of twin studies put the heritability of ADHD at about 74%, which means most of the difference in ADHD traits between people is linked to genetic differences (Faraone and Larsson, Molecular Psychiatry, 2019). Other risk factors include being born very early or at a low birth weight. The CDC notes that research does not support the popular view that ADHD is caused by eating too much sugar, watching too much television or parenting style (CDC).

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How does ADHD show up in adults?

Adult ADHD tends to look quieter than the childhood version. The NHS lists signs such as carelessness and a lack of attention to detail, starting new tasks before finishing old ones, poor organizational skills, losing or misplacing things, forgetfulness, restlessness, and difficulty waiting your turn (NHS). Everyone has days like this. In ADHD the pattern is constant, it goes back to childhood, and it causes real problems at work, at home or in relationships.

How does ADHD affect reading?

Reading asks for exactly the skills ADHD makes harder: holding a sentence in mind while the next one arrives, ignoring the noise around you, and keeping going through a page that offers no instant reward. So many adults with ADHD reach the end of a paragraph with no idea what it said, reread the same line several times, or put a book down after a few pages. Our article on why ADHD makes reading harder explains the brain science, and the guide to executive function and reading goes deeper into working memory and planning.

How does ADHD affect everyday work?

At work the same skills show up as missed deadlines, half-finished projects, long emails left unread and meetings where your mind wanders off. Many adults with ADHD also describe the other side: deep focus on work they find interesting, quick ideas and energy under pressure. The trouble is that attention follows interest rather than importance, so the dull but urgent task is the one that slips.

How do adults get assessed for ADHD?

Assessment usually starts with a short screening questionnaire. The six-question Adult ADHD Self-Report Scale (ASRS-v1.1) was developed with the World Health Organization for this first step (Kessler et al., Psychological Medicine, 2005), and you can take it in about two minutes with our free ADHD self-test. The ADHD self-test is a screener, not a diagnosis. It tells you whether your answers are worth raising with a doctor.

Only a doctor can diagnose ADHD. In the UK the NHS refers adults to a specialist, such as a psychiatrist, for a full assessment (NHS). The assessment covers your symptoms today and in childhood, often with input from someone who knew you then, and it checks for other conditions that can look similar, such as anxiety, depression or sleep problems. Under the DSM-5 criteria used by clinicians, adults need at least five signs of inattention or of hyperactivity-impulsivity, several of them present before age 12 and in two or more settings, such as home and work (CDC).

What helps after a diagnosis?

The UK's National Institute for Health and Care Excellence recommends that adults with ADHD get support that fits their needs, including changes to their environment, medication when symptoms still cause significant problems, and psychological support such as cognitive behavioral therapy (NICE guideline NG87). Your doctor is the right person to talk these options through with. Practical habits help alongside treatment, and our reading strategies for adults with ADHD are a good place to start with reading.

Conclusion: Knowing Is the First Step

ADHD is common, it is largely genetic, and it is nobody's fault. If the signs in this guide sound familiar, a two-minute screener is an easy first step, and a conversation with your doctor is the next one. Whatever the answer, knowing how your attention works makes it easier to choose tools and habits that work with it rather than against it.

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