Attention deficit hyperactivity disorder and schizophrenia are two different disorders that can profoundly affect a person's life. While they have many differences, they also share some characteristics.

For this reason, some scientists have been looking into a possible link between them.

Attention deficit hyperactivity disorder (ADHD) is a chronic condition that involves behavioral symptoms, including inattentiveness, hyperactivity, and impulsiveness.

It is a neurodevelopmental disorder, and diagnosis usually takes place before the age of 12 years. Although symptoms tend to improve with age, some people continue to have symptoms as adults.

During childhood, ADHD is more common in males than in females, but the prevalence becomes relatively even in adulthood. It is possible that fewer girls receive a diagnosis because they show symptoms differently, meaning that caregivers or teachers may not notice them.

The Centers for Disease Control and Prevention (CDC) estimate that, in 2016, about 6.1 million children living in the United States had received a diagnosis of ADHD.

Schizophrenia is a long-term mental health condition that affects how a person thinks, feels, and behaves. It involves psychosis and other symptoms, including inattention.

Schizophrenia is slightly more common in males than females. Symptoms often begin between the ages of 16 and 30 years, but it can sometimes appear during childhood.

Around 1 percent of people in the U.S. have schizophrenia, according to the National Alliance on Mental Illness (NAMI).

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A lack of focus is common with ADHD and with schizophrenia.

Various studies have identified some similarities between ADHD and schizophrenia and a possible overlap.

The conclusions of researchers include the following:

  • People with schizophrenia often have symptoms of other psychiatric disorders, including ADHD, in early adolescence.
  • Children and teenagers with ADHD may be 4.3 times more likely to develop schizophrenia as adults than people without ADHD.
  • Close relatives of people with ADHD may be more likely than second-degree relatives to receive a diagnosis of schizophrenia, suggesting that it may have a genetic component.

In 2013, a team of geneticists looking at ADHD in children and schizophrenia in adults found evidence of a "small but significant shared genetic susceptibility."

The exact causes of ADHD and schizophrenia are not clear, but a combination of genetic and environmental factors may increase the risk of both.

A person with specific genetic features may develop symptoms if they encounter certain triggers, whether this exposure occurs before birth or during childhood and adolescence.

ADHD

Factors that may contribute to ADHD include:

  • Genetic features: ADHD can run in families.
  • Environmental factors: Exposure to toxic materials, including as a fetus, may increase the risk.
  • Developmental issues: Problems with the central nervous system at important stages of development may result in ADHD.

Schizophrenia

Factors that may increase a person's likelihood of developing schizophrenia include:

  • Genetic features: Genetic factors appear to play a role. Having a close family member with schizophrenia may increase the risk.
  • Brain development: Research shows that some individuals with schizophrenia have subtle differences in their brain structure.
  • Neurotransmitters: An imbalance between dopamine and serotonin, the chemical messengers in the brain, may have a connection with schizophrenia. Drugs that alter the levels of these chemicals appear to relieve schizophrenia symptoms.
  • Pregnancy and birth complications: A low birth weight, premature labor, or insufficient oxygen during birth are more likely to have affected people with schizophrenia.

ADHD and schizophrenia

Both conditions involve neurodevelopmental changes and can run in families. However, researchers do not yet know whether the same changes relate to both conditions or to what extent these underlying features overlap.

The risk factors for ADHD and schizophrenia are not the same, but they may overlap. For both conditions, some risk factors may affect a person before birth, while others come into effect during childhood and adolescence.

ADHD

Risk factors for ADHD include:

  • a family history of ADHD or another mental health disorder
  • exposure to certain substances while in the womb
  • a lack of specific nutrients, such as folate, zinc, magnesium, and polyunsaturated acids

Schizophrenia

There is growing evidence that some environmental factors can lead to neurodevelopmental problems that result in schizophrenia.

Possible environmental factors include:

  • exposure to certain substances, such as cannabis or lead, before birth
  • nutritional deficits, including low levels of folic acid and iron
  • rubella or other maternal infections during pregnancy
  • maternal stress during pregnancy
  • infections during childhood and adolescence
  • deficiency in iron and vitamin D resulting in decreased choline during pregnancy
  • an increase in immune system activity due to inflammation or autoimmune disease
  • taking mind-altering drugs as teenagers or young adults

Some researchers have suggested that there may be a link between low birth weight and mental illness, possibly including schizophrenia. However, they have noted that more evidence is necessary to confirm this.

The authors of a 2011 review concluded:

"It appears increasingly likely that a large portion, if not the majority, of schizophrenia cases can be accounted for by interactions between environmental and genetic factors and by other mechanisms involving the subtle interplay between environments and genes."

ADHD and schizophrenia

Scientists believe that there is an overlap in the factors that can lead to ADHD and schizophrenia.

Genetic factors: A person who has a close relative with schizophrenia may be more likely to develop ADHD. Researchers say that up to 80 percent of cases of schizophrenia and between 60 and 80 percent of cases of ADHD may result from inheritance.

Changes in underlying brain mechanisms: Some neurological factors are common to both conditions.

Environmental influences: Exposure to specific influences before birth and during childhood appears to increase the risk of both conditions.

Shared history: People who have schizophrenia are more likely to have had a diagnosis of ADHD during childhood.

Does ADHD medication lead to schizophrenia?

Some people who use stimulant medication to relieve the symptoms of ADHD go on to experience symptoms of psychosis.

However, it is unclear whether using stimulants to treat ADHD increases the risk of schizophrenia or schizophrenia-type symptoms, specifically psychosis. These symptoms may have appeared without the use of stimulant medication.

Exposure to psychostimulant drugs does appear to increase the risk of psychosis. Psychosis that appears at a younger age is more likely to result from the use of psychostimulant drugs.

However, it remains unclear whether psychosis results from the use of the drugs or whether these individuals were already susceptible to psychosis.

In addition, the type of psychosis that people with ADHD experience tends to be different from that in people with schizophrenia as it involves brief mental changes rather than full hallucinations.

The symptoms of ADHD and schizophrenia are different, but they overlap in the area of inattention.

ADHD

There are three different types of ADHD:

  • inattentive ADHD
  • hyperactive and impulsive ADHD
  • combined inattentive and hyperactive ADHD

Symptoms of inattentiveness include:

  • having a short attention span and getting easily distracted
  • making careless mistakes during activities
  • appearing not to listen
  • being unable to follow instructions and complete tasks
  • having problems with organizing tasks
  • being forgetful or frequently losing things
  • avoiding tasks that require mental effort

Symptoms of hyperactivity and impulsiveness include:

  • fidgeting constantly and being unable to sit still
  • being unable to engage quietly in leisure activities
  • lacking concentration
  • talking excessively
  • interrupting other people's conversations or intruding on their activities
  • being restless
  • running excessively or climbing in inappropriate situations
  • acting without thinking
  • having little or no sense of danger

Not everyone who has ADHD will have hyperactivity as a symptom.

Schizophrenia

Doctors categorize the symptoms of schizophrenia as either positive, negative, or cognitive.

Positive symptoms include:

  • hallucinations
  • delusions, such as believing that the government is pursuing them
  • paranoid thoughts
  • agitated or excessive body movements
  • agitated or inappropriate behavior

Negative symptoms include:

  • social withdrawal
  • not caring about appearance and personal hygiene
  • reduced emotional expression
  • losing interest and motivation
  • trouble concentrating
  • changes in sleep habits
  • feeling unable to leave the house
  • a decrease in conversation and speaking

Cognitive symptoms include:

  • having confused or disorganized thoughts
  • an inability to understand information and make decisions
  • a lack of focus and attention
  • difficulty using learned information immediately

ADHD and schizophrenia

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People with both conditions may need help to overcome problems of inattention.

ADHD and schizophrenia may share some symptoms.

For example, attention problems affect both people with ADHD and people with schizophrenia.

However, some researchers have suggested that the type of inattention involved in ADHD may be different from that in schizophrenia and that the underlying neurological features are also different.

Thought disorders and psychosis can also occur in both schizophrenia and ADHD. People with schizophrenia often experience psychotic episodes, which can involve hallucinations, delusions, and disturbed thoughts.

Psychosis is not typical of ADHD, but around 10 percent of people with this condition experience psychotic symptoms. One theory is that the stimulant drugs that doctors prescribe to treat ADHD may trigger these psychotic symptoms.

Research has shown that some people whose genetic makeup puts them at high risk of schizophrenia will meet the criteria for a diagnosis of ADHD.

Some people with ADHD also have hyperactivity, but this is not a symptom of schizophrenia.

Doctors use different criteria to diagnose ADHD and schizophrenia.

ADHD

There is no specific test to diagnose ADHD. A doctor will ask the individual about their medical history and symptoms and then conduct a medical examination to rule out other causes. The doctor will compare the symptoms with ADHD criteria and rating scales to make a diagnosis.

Diagnosis usually happens in childhood, often before the age of 12 years.

Schizophrenia

A doctor will ask the individual about their medical history and the symptoms that they are experiencing. They will also ensure that the symptoms are not due to medication, substance abuse, or another medical condition.

The doctor may carry out alcohol and drug screening or imaging studies, such as an MRI or CT scan.

If a doctor or mental health professional suspects schizophrenia, they will perform a psychiatric evaluation and compare the symptoms with diagnostic criteria for schizophrenia.

According to the NAMI, schizophrenia usually presents in males who are in their late teenage years or early 20s, while the onset tends to occur in females aged about 25–35 years.

ADHD and schizophrenia

A doctor will diagnose both ADHD and schizophrenia by comparing symptoms to those on a list in the latest edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).

The DSM-5 classifies schizophrenia and ADHD as completely different conditions. Schizophrenia is a psychotic disorder, while ADHD is a neurobehavioral disorder.

There is no cure for ADHD or schizophrenia, but treatment can help relieve symptoms.

ADHD

Treatment options include:

  • stimulant drugs to boost and balance brain chemical levels
  • nonstimulant medicines, which take longer to work than stimulants but can improve attention, focus, and impulsiveness
  • behavioral therapy to help people manage and change their behavior

Schizophrenia

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Counseling can help people with ADHD or schizophrenia, but each condition will need a different type of counseling and specific types of medication.

Treatment options for managing the symptoms of schizophrenia include medications and psychosocial therapy.

Treatment may include:

Antipsychotic drugs: These aim to manage symptoms by controlling levels of the brain chemical dopamine.

Psychosocial therapy: This combines psychotherapy and social training to provide support, education, and guidance to people with schizophrenia.

Hospitalization: This may be necessary when a person's symptoms are severe.

Electroconvulsive therapy (ECT): People whose symptoms do not respond to medication may benefit from ECT.

Similarities and differences

The treatment options for ADHD and schizophrenia are different. In both cases, doctors aim to manage symptoms rather than cure the condition.

For ADHD, a doctor may prescribe stimulants that increase dopamine levels in the brain. In some people, this type of drug may trigger psychosis.

For schizophrenia, a doctor will prescribe antipsychotic drugs that block the effect of dopamine.

ADHD and schizophrenia are different conditions, but they can occur together, and there may be some overlap between them. Some researchers believe that they share some underlying features. However, exactly how they relate to each other remains unclear.

Both conditions involve inattention, for example, but it is not apparent if this is the same kind of inattention or if it has the same cause.

ADHD tends to start at a younger age, and symptoms often improve with time, although they can continue into adulthood. Some people with ADHD go on to develop symptoms of schizophrenia, including psychosis.

Schizophrenia is usually a long-term condition. Treatment can relieve symptoms and enable many people to live a normal life, but relapse is likely if they do not follow their treatment plan. A person with schizophrenia may also have symptoms of ADHD.

ADHD is far more common than schizophrenia. Many people have ADHD and never develop schizophrenia. There is no evidence that one condition causes the other.

The exact link between the two conditions needs further investigation.

Q:

Is it likely that some people get an ADHD diagnosis when they actually have the early symptoms of schizophrenia?

A:

Probably not. As you can see, the issue is complex, and while there is some overlap in the symptoms, the diagnostic criteria in the DSM-5 exist to help clinicians diagnose both ADHD and schizophrenia.

Someone may meet the criteria for ADHD in their childhood and then receive a diagnosis of schizophrenia years later, but this does not mean that the first diagnosis was wrong.

It is more likely to indicate that the symptoms of schizophrenia were not present at the time of the ADHD diagnosis.

Timothy J. Legg, PhD, CRNP Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.