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Can ADHD Cause “Brain Fog”?

Written by Carlos Tello, PhD (Molecular Biology) | Last updated:
Puya Yazdi
Medically reviewed by
Puya Yazdi, MD | Written by Carlos Tello, PhD (Molecular Biology) | Last updated:
Can ADHD Cause Brain Fog

ADHD is a psychological disorder combining inattention and hyperactivity. People with ADHD often experience “brain fog” symptoms such as forgetfulness, difficulty focusing, and slow thinking. Read on to learn more about ADHD “brain fog” and its symptoms.

Understanding Brain Changes in ADHD

What Is ADHD?

Attention-deficit/hyperactivity disorder (ADHD) is a common psychological disorder with inattention and hyperactivity/impulsivity. Depending on which symptoms predominate, ADHD can be classified into three subtypes [1, 2, 3+, 4+]:

  • Inattentive (ADHD-I): with reduced attention, difficulty staying focused and organizing tasks, and forgetfulness.
  • Hyperactive (ADHD-H): with excessive talking and moving, discomfort if forced to stay still, and tendency to interrupt others and take risks without thinking of consequences.
  • Combined (ADHD-C): with a mix of both inattentive and hyperactive symptoms.

ADHD reduces school performance, causes problems in social relationships, increases the risk of dangerous behavior (such as drug abuse), and is linked to school dropout and reduced earning [5+, 6+, 7+].

ADHD is a common psychological disorder. People with ADHD have inattention and hyperactivity/impulsivity symptoms.

Sluggish Cognitive Tempo vs ADHD

Sluggish cognitive tempo (SCT), also known as concentration deficit disorder, is a constellation of symptoms such as daydreaming, confusion, and slow thinking. Although initially grouped together with ADHD-I, further studies have possibly revealed their differences [8+, 9+, 10+, 11+]. Though it must be said, that this is not without some controversy and the science on this has not been fully decided.

ADHD-I is more impairing in executive function, time management, and motivation, while SCT worsens academic performance, selective attention, self-organization, problem-solving, self-discipline, and control of emotions [12+, 13+, 11+, 14+].

Nevertheless, SCT is more frequent in people with ADHD. Three studies on over 1k adults and 2k children and adolescents found SCT symptoms in 40-60% of those with ADHD. The combination of ADHD and SCT is more impairing than either condition alone [12, 14, 15].

Sluggish cognitive tempo is similar to ADHD; its main symptoms are concentration and selective attention deficits.

How Does ADHD Affect the Brain?

Brain imaging studies of children and adults with ADHD found multiple structural anomalies in regions controlling working memory and attention (such as the cortex, basal ganglia, and cerebellum). These include [16, 2, 17, 1, 18+]:

  • Reduced size
  • Lower gray matter density
  • Changes in white matter integrity
  • Delayed cortex maturation in children and reduced thickness in adults

What’s more, people with ADHD show reduced activity in some brain regions involved in executive function and attention (cortex, anterior cingulate gyrus, thalamus, and cerebellum) and overactivation of those promoting daydreaming and mind-wandering (the default-mode network) [19, 20, 17].

People with ADHD also have impaired dopamine and noradrenaline transmission. This can be due to mutations in the proteins responsible for the production, sensing, transport, and breakdown of these neurotransmitters [21+, 22, 23].

Similarly, ADHD is accompanied by disturbances in the transmission of serotonin, acetylcholine, and glutamate in some people [24, 25, 26].

Studies suggest that ADHD may cause distinct brain changes. People with ADHD may also have neurotransmitter abnormalities. More research is needed.

“Brain Fog” and ADHD

What Is “Brain Fog”?

Brain fog“, also known as “mental fog,” “clouding of consciousness,” and “cognitive dysfunction,” is an unofficial term to describe a constellation of cognitive symptoms such as [27, 28]:

  • Reduced mental clarity and cognitive function
  • Difficulty focusing and multitasking
  • Loss of short- and long-term memory
  • Slow thinking
  • Confusion
  • Fatigue

Some researchers believe “brain fog” is caused by inflammation or free radicals damaging the brain regions responsible for emotions, cognitive, and executive function – the limbic system [27, 28, 29+].

People with ADHD often report forgetfulness and difficulty focusing. In turn, those with sluggish cognitive tempo tend to feel spaced out, confused, and lost in thoughts. But does this mean that these conditions are “brain fog” triggers? Let’s look at the research to find out.

In any case, keep in mind that the link between ADHD and “brain fog” symptoms has been mainly investigated in cohort studies. While these studies can associate a condition with certain symptoms, they cannot establish it as the cause of these symptoms.

“Brain fog” is an unofficial term that describes a constellation of subjective symptoms: mild cognitive difficulties, memory problems, and fatigue.

“Brain Fog” and ADHD

Children and Adolescents with ADHD

In 9 studies on over 5k children and adolescents, ADHD was associated with problems in the following cognitive areas [30, 31, 32, 33, 34, 35, 36, 37, 38]:

  • Working and long-term memory
  • Processing speed
  • Language comprehension
  • Sustained attention
  • Executive function
  • Organizational skills

Most children belong to the combined ADHD subtype. In comparison to the others, this variant often has more severe symptoms [39+, 40+, 41+, 42+].

Children with ADHD-H tend to be more aggressive, active, and impulsive. In turn, those with ADHD-I often have more evident “brain fog” symptoms such as reduced processing speed and sustained attention [39+, 43, 44, 45, 46, 47+, 48].

Nevertheless, the differences among subtypes gradually disappear while the child grows and are no longer evident during adolescence [42].

Some studies have associated ADHD with cognitive problems in children and adolescents.

Adults with ADHD

Although ADHD was initially thought to be a childhood disorder, long-term follow-up studies revealed that 40-60% of diagnosed children will maintain it during their adulthood [49+, 50+, 17].

Seven studies on over 1300 adults with ADHD found problems in the following cognitive areas [51, 52, 53, 54, 55, 56, 57]:

  • Executive function
  • Sustained attention
  • Working memory
  • Language comprehension

Adults with ADHD tend to have difficulties in carrying out tasks due to their inattention. Conversely, hyperactivity is greatly reduced and only remains as restlessness. Their increased risk of substance abuse may further cause cognitive impairment [58+, 17, 59+].

ADHD symptoms tend to be milder in elderly people and don’t seem to be associated with the risk of developing dementia [60, 61, 62].

Though studies have linked adult ADHD with cognitive issues and restlessness, more large-scale studies are needed.

“Brain Fog” and Sluggish Cognitive Tempo

Overlapping Symptoms

Sluggish cognitive tempo is thought to be linked to “brain fog.” Its main symptoms include [8+, 9+]:

  • Drowsiness
  • Daydreaming
  • Frequent staring
  • Confusion
  • Slow thinking and task completion
  • Reduced activity and persistence
  • Difficulty focusing attention
Sluggish cognitive tempo causes attention difficulties and slow thinking. It appears to be linked with “brain fog.”

Limitations and Caveats

The studies investigating the association between ADHD and “brain fog” symptoms were generally cohort studies, which can’t establish a cause-effect relationship.

Additionally, they differed in factors such as the age, gender, ADHD subtype, or medication history of their populations. This makes it sometimes difficult to compare studies.


ADHD is a common disorder among both children and adults. It is marked by inattention and hyperactivity/impulsivity. Ongoing research is exploring whether and to what extent ADHD affects cognitive function and brain health.

Sluggish cognitive tempo is similar to ADHD but thought to be marked by selective attention problems and concentration deficits, though there remains some controversy. A number of people with ADHD also have sluggish cognitive tempo, which overlaps with “brain fog”: forgetfulness, fatigue, and reduced mental clarity.

According to some studies, ADHD changes the brain and may lead to neurotransmitter abnormalities. ADHD has been linked with cognitive problems in children and adults that are subjectively described as “brain fog.” More research is needed.

Learn More

About the Author

Carlos Tello

Carlos Tello

PhD (Molecular Biology)
Carlos received his PhD and MS from the Universidad de Sevilla.
Carlos spent 9 years in the laboratory investigating mineral transport in plants. He then started working as a freelancer, mainly in science writing, editing, and consulting. Carlos is passionate about learning the mechanisms behind biological processes and communicating science to both academic and non-academic audiences. He strongly believes that scientific literacy is crucial to maintain a healthy lifestyle and avoid falling for scams.


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