Causes and risk factors

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The appearance of ADHD is not due to a single cause. As with other neurodevelopmental disorders, it is highly influenced by genetics and the environment. Exposure to risk factors does not necessarily lead to the disorder.

The main factors influencing the development of ADHD are:


There are many genes involved in the development of ADHD. Some are related to the activity of neurotransmitters (molecules responsible for transmitting the electrical impulse from one neuron to another). It is especially related to dopamine, a neurotransmitter, as well as others, such as norepinephrine and serotonin.  ADHD has also been linked to chromosomal abnormalities.

These same alterations occur in related disorders, such as autism spectrum disorders and Tourette syndrome.


In the perinatal stage (pregnancy and childbirth) and the first years of life, the brain is considered to be in the process of maturation when any external alteration can affect this process. Examples are infections, metabolic changes during pregnancy and complications during childbirth.  

In addition, social circumstances at an early age can provoke maladaptive responses and lead to disorders later in life; for example, suffering violence during childhood. These environmental factors can activate or decrease the activity of some gene and alter the neuroendocrine and immune systems.

Inheritability of ADHD is 70%, according to studies conducted with pairs of twins. That is, the risk that children of parents with ADHD also have the disorder is 7 out of 10.  

The risk of other siblings also developing ADHD is increased by 5. The chance that the twin of a person with ADHD also suffers from the disorder is increased by 12-16 times.

Risk factors related to the mother's health:

Pregnant woman smoking

Smoking during pregnancy

Cannabis, pills and a syringe

Consuming toxic substances

Beer mug and wine glass

Drinking alcohol

Woman sweating from physical exertion with an accelerated heart rate


Icon of a woman under the age of 21

Age of the mother at birth: having children before the age of 21 increases the risk of children having ADHD by 1.5 times.

Icon of a woman over 45 years old

Also, older mothers (45-49 years) have the risk of their child having ADHD increased by 1.26.

Thyroid gland with a downward pointing arrow indicating hypothyroidism

Maternal hypothyroidism during pregnancy also increases this risk.

Position of the premature baby

Early term births and especially low weight babies for their gestational age.

Risk factors related to external agents during the perinatal and postnatal period:

Toxics signal

Poisoning or exposure to possible toxins: e.g., lead, pesticides or biphenyl polychlorinate.

Baby and fever thermometer

Deficiency or excess factors (e.g., excess sugars, zinc, magnesium, omega-3 deficiency), serious head injuries or infections.

Examples of these factors are educational style (e.g., a conflictive family environment), education received from parents (e.g., inconsistent discipline) or physical or psychological abuse. These factors would not cause the disorder, but may promote its development. They can affect symptom severity or the intensity of their expression, or the severity of the ADHD itself.

Substantiated information by:

Marta Garcia Giral
Montse Vila
Rosa Nicolau

Published: 18 February 2022
Updated: 18 February 2022

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