What causes ADHD?

Attention-deficit/hyperactivity disorder (ADHD) is a common developmental issue. Children and adults with ADHD may have trouble with focus, hyperactivity, and impulse control. While some people may falsely believe ADHD is the result of poor parenting or too much sugar or screen time, the causes aren’t fully understood. It’s likely that many different things play a role.

"There are clearly genetic factors, but genes don't explain it all," says Andrew Gilbert, a psychiatrist in New York City who specializes in ADHD diagnosis and treatment. "It appears that environmental factors, such as perinatal stress, low birth weight, and maternal smoking during pregnancy can contribute. Recent studies have recognized differences in brain development and maturation in children and adolescents with ADHD compared to those without the disorder."

With that in mind, here's what experts understand about what causes ADHD.

Risk factors for ADHD

These factors may all increase the risk of a person developing ADHD.

Genes

ADHD often runs in a family. In other words, a person is more likely to have ADHD if a blood relative, such as a parent or sibling, have the disorder. For example, if a child has ADHD, there’s a 25 percent chance their parent has it, as well, according to the American Academy of Pediatrics.

Brain differences

The brain of a person with ADHD may not be structured in the same way as a person who doesn’t have the disorder. Parts of it that control focus may be less active than other parts. It’s also possible that the nerve cells within the brain transmit signals in a different way.

Exposures during pregnancy

Pregnancy is a critical period for fetal brain development. When a fetus is exposed to certain substances during this time, it can affect the way their brain functions throughout life. Some of these substances have been specifically linked to a higher risk of ADHD. They include alcohol, illicit drugs, and tobacco. They also include potentially dangerous chemicals in the environment.

Some risky exposures may occur during early childhood. For example, lead found mainly in paint and pipes in older buildings has been linked to a short attention span, among other behavioral issues.

Preterm birth and low birth weight

Studies suggest that babies born early are more likely to have ADHD than those who were carried to term. The same goes for babies with a low birth weight, independent of other factors.

What doesn’t cause ADHD

ADHD is essentially an issue of genetics and brain development. There’s no evidence that it’s caused by eating too much sugar, consuming food additives, or having allergies. Vaccines do not cause ADHD. Spending excessive time in front of a TV, smartphone, or computer may affect how people approach tasks, but science doesn’t support it as a cause of ADHD, either.

If you believe you or a loved one might have ADHD, it’s important to see a healthcare provider (HCP) for diagnosis and treatment. "Effective treatments [can help], such as stimulants, target neurotransmitters, including dopamine and norepinephrine, which are involved in attention-regulating brain circuits," Gilbert says. The sooner you see an HCP, the sooner you can feel better.