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ADHD is caused by a combination of genetic and environmental factors, with genetics being the primary contributor. This guide explains what research tells us about the causes of ADHD, the brain differences involved and what does not cause ADHD.
ADHD is caused by a combination of genetic and environmental factors. Genetics is the most significant contributing factor, with twin studies estimating heritability at around 74 percent. ADHD involves identifiable differences in the development and function of brain circuits involved in attention regulation, impulse control and executive function, particularly those involving dopamine and norepinephrine signalling. Environmental factors including prenatal exposure to nicotine, premature birth and early childhood adversity may contribute modestly to ADHD risk, particularly in the context of genetic vulnerability.
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Genetics is the most significant contributing factor to ADHD. Twin studies consistently estimate ADHD heritability at around 74 percent. ADHD is polygenic: many common genetic variants each contribute a small amount to risk. Genome-wide association studies have identified multiple genetic variants associated with ADHD, including variants involved in dopamine signalling pathways. Family studies confirm that ADHD runs strongly in families.
Neuroimaging research has identified consistent differences in brain structure and function in people with ADHD. These include differences in the prefrontal cortex, which is responsible for executive function and impulse control, the striatum, which is involved in reward processing and motivation, and the cerebellum. People with ADHD on average show slightly delayed cortical maturation compared to neurotypical peers, though the brain does continue to develop. These brain differences reflect the neurodevelopmental basis of ADHD.
ADHD involves differences in the functioning of the dopamine and norepinephrine neurotransmitter systems. Dopamine plays a key role in reward, motivation and attention regulation. Norepinephrine is involved in arousal and attentional focus. The effectiveness of stimulant medications in ADHD, which work primarily by increasing dopamine and norepinephrine availability in key brain circuits, supports the involvement of these systems. These are not simple deficits but differences in regulation and signalling.
Several prenatal and perinatal factors have been associated with modestly increased ADHD risk in epidemiological studies. Prenatal exposure to nicotine through maternal smoking is the most consistently identified environmental risk factor. Premature birth, very low birth weight and prenatal alcohol exposure have also been associated with increased risk. These factors do not cause ADHD on their own in most cases and cannot be used to predict whether a specific individual will develop ADHD.
Significant early childhood adversity, including neglect, abuse and institutional deprivation, is associated with an increased risk of ADHD symptoms. The relationship is complex: early adversity may unmask genetic vulnerability or may produce ADHD-like symptoms through different neurobiological pathways. Some research suggests that children who have experienced severe early adversity may show ADHD symptoms that differ in some ways from genetically driven ADHD.
Several widely held beliefs about the causes of ADHD are not supported by evidence. Sugar consumption does not cause ADHD: controlled experimental studies have found no causal link between dietary sugar and ADHD symptoms. Screen time does not cause ADHD: while excessive screen time may be correlated with ADHD in some studies, this reflects existing ADHD rather than causing it. Poor parenting does not cause ADHD. Vaccines do not cause ADHD.
For related information see our articles on ADHD and Genetics and ADHD Explained.
Genetics is the main cause of ADHD, with heritability estimated at around 74 percent from twin studies. ADHD involves differences in dopamine and norepinephrine signalling systems and in the development of brain circuits involved in attention regulation and impulse control. Environmental factors including prenatal nicotine exposure and premature birth may contribute modestly to risk.
No. The belief that sugar causes ADHD or worsens ADHD symptoms has been studied extensively and is not supported by controlled research. While some parents report that their child’s behaviour changes after sugar consumption, controlled double-blind studies have not confirmed a causal link. The belief persists because of the combination of expectation effects and the natural energy and excitement associated with situations where sweet foods are consumed, such as parties.
No. Screen time does not cause ADHD. Studies showing correlations between screen time and ADHD symptoms generally reflect the fact that children with ADHD are more drawn to the immediate reinforcement of screens rather than screens causing ADHD. ADHD is a neurodevelopmental condition with a strong genetic basis. Managing screen time may be helpful for children with ADHD for practical reasons, but it does not address the underlying condition.
Visit our Understanding ADHD hub for more guides on signs, diagnosis, types, medication, executive function and co-occurring conditions.
The information in this article is provided for educational purposes only and is not intended as medical advice. If you have concerns about ADHD or any neurodevelopmental condition, speak to a qualified healthcare professional. SENDhelp Education Limited accepts no responsibility or liability for any loss or damage arising from reliance on this content. Any links to third-party websites are provided for convenience only and do not constitute endorsement of their content.
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