--- title: What causes ADHD description: If you’re looking for one exact cause of ADHD, you won’t find it. But science points to key factors that play a role in why people have this common condition. slug: what-causes-adhd author: Gail Belsky reviewer: Andrew Kahn, PsyD published: '2024-09-24T00:00:00.000Z' date_modified: '2026-04-02T00:00:00.000Z' thumbnail: https://cdn-images.understood.org/p0qf7j048i0q/4VdhvjYSm0HWEMq28ghbD2/8aaae140235a329e6fa6650b0f96b129/G2150751006.png source_url: https://www.understood.org/en/articles/what-causes-adhd lang: en --- # What causes ADHD Researchers have been looking into what causes ADHD for decades. While they haven’t found an exact cause of ADHD, they’ve identified two key factors that play major roles. The first is differences in how the brain develops and functions. The second is genetics — [ADHD very often runs in families](https://www.nimh.nih.gov/health/topics/attention-deficit-hyperactivity-disorder-adhd). Some researchers have also looked into potential outside risk factors, like exposure to chemicals. In the end, the cause of ADHD may be a combination of factors and not just one. ## ADHD and the brain ADHD is a neurodevelopmental disorder, meaning it’s a difference in how the brain develops and functions. Brain imaging studies have shown that the brain develops similarly in kids who do and don’t have ADHD — but at different rates.  With ADHD, there’s a delay in the [development in certain areas of the brain](https://www.nimh.nih.gov/health/topics/attention-deficit-hyperactivity-disorder-adhd) that are involved in what’s known as [executive function](https://www.understood.org/en/articles/what-is-executive-function). This is a set of mental skills that allow us to focus, plan, manage time, and organize. Kids and young adults with ADHD tend to be three to five years behind in developing those areas of the brain. A large-scale study using brain imaging scans also showed that [some areas of the brain](https://doi.org/10.1016/S2215-0366%2817%2930049-4) are smaller in people with ADHD. These areas include: - Accumben: Controls mood, motivation, and experiencing pleasure - Amygdala: Plays a role in emotional control and prioritizing actions - Caudate: Key in decision-making and purposeful behavior - Hippocampus: Responsible for long-term and [working memory](https://www.understood.org/en/articles/working-memory-what-it-is-and-how-it-works) - Putamen: Helps with learning, memory, and regulation of movement Researchers have also found differences in how the brain functions. These differences involve: - The level of activity in certain areas of the brain - The chemical signals that travel through the brain - Interaction between [certain areas of the brain](https://www.nih.gov/news-events/news-releases/nih-researchers-identify-brain-connections-associated-adhd-youth) ## Genes and heredity If you have ADHD, chances are that others in your family do, too. Over the years, twin, family, and adoption studies have shown a [strong genetic connection](https://doi.org/10.1038/s41380-018-0070-0%20). If you have ADHD, there’s a one-in-four chance that one of your parents also has it. And it’s likely that another close family member, like a sibling, will have ADHD. (ADHD isn’t something parents “give their kids.” It’s just something in our genetic code.) Often, undiagnosed parents will recognize signs of ADHD in themselves when their child is diagnosed with ADHD. More and more adults, especially women, are now getting evaluated for ADHD. ## Connections to other disorders There are a number of [disorders that often co-occur with ADHD](https://www.understood.org/en/articles/adhd-comorbidity). They don’t *cause *ADHD, but researchers are looking into possible links — including genetic links. Conditions that often co-occur with ADHD include:  **Learning disorders: **[Certain learning disorders often co-occur with ADHD](https://doi.org/10.12998/wjcc.v7.i17.2420), although the exact amount of overlap isn’t clear. The learning differences that most often co-occur are [written expression disorder](https://www.understood.org/en/articles/what-is-written-expression-disorder), [dyslexia](https://www.understood.org/en/articles/what-is-dyslexia), and [dyscalculia](https://www.understood.org/en/articles/what-is-dyscalculia). **Autism spectrum disorder (ASD):** Kids who have ADHD sometimes also have ASD. When someone has [both ADHD and ASD](https://doi.org/10.12998/wjcc.v7.i17.2420), you may hear it being called [AuDHD](https://www.understood.org/en/articles/what-is-audhd). **Mental health conditions:** A number of mental health disorders often co-occur with ADHD. In adults, the ones that overlap most are mood disorders like [depression and anxiety](https://doi.org/10.1186/s12888-017-1463-3). In kids, the [conditions that co-occur most](https://doi.org/10.12998/wjcc.v7.i17.2420) include learning disorders, mood disorders like depression and anxiety, disruptive mood dysregulation disorder (DMDD), and oppositional defiant disorder (ODD). ## Environmental factors  Genetics aren’t a part of all ADHD cases. Researchers are also looking into outside or “environmental” factors that might play a role. None of these factors are shown to *cause *ADHD, but they may increase the risk of having it.  Here are some of the factors that researchers are looking at:  - [Exposure to certain chemicals](https://doi.org/10.1007/s11121-023-01601-6) - [Exposure to heavy metals and lead](https://doi.org/10.1186/s12889-024-19742-w) - [Prenatal exposure to alcohol or tobacco](https://doi.org/10.1001/jamanetworkopen.2022.1957) - [Trauma](https://doi.org/10.1007/s12402-017-0241-x) - [Pre-pregnancy obesity](https://doi.org/10.3390/ijerph16040667) - [Parental stress, particularly in mothers](https://doi.org/10.1007/s11121-022-01383-3) It’s important to know that experiencing any of those factors doesn’t mean you or your children will have ADHD. ## Watch: An expert’s take on genes and ADHD Understood Expert Dr. Ari Tuckman sorts fact from fiction about what causes ADHD. --- ```json [{"@context":"https://schema.org","@type":"WebPage","@id":"https://www.understood.org/en/articles/what-causes-adhd#webpage","url":"https://www.understood.org/en/articles/what-causes-adhd","description":"If you’re looking for one exact cause of ADHD, you won’t find it. 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