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The ADHD-gut connection: The relationship between Attention Deficit Hyperactivity Disorder and Gut organisms

adhd adhd mental health adhd support adhd wellbeing gut brain health gut health Nov 30, 2021

What is ADHD?

Attention Deficit Hyperactivity Disorder (ADHD) is a disorder that affects more than 5% of the population. ADHD is classified as a neurodevelopmental disorder and is marked by three main categories: hyperactivity, inattention, and a combination of both. ADHD affects both children and adults. ADHD symptoms can be debilitating, and many people struggle to maintain their day-to-day lives because of them.

Common symptoms of ADHD

Common symptoms of Attention Deficit Hyperactivity Disorder include difficulty with concentration, forgetfulness, impulsive behavior, and overall challenges with executive functioning. ADHD can affect every aspect of life, but ADHD symptoms are often most prominent at work and in learning environments. ADHD can make it difficult to complete tasks on time and these challenges can result in poor self-esteem throughout life.

Possible causes of Attention Deficit Hyperactivity Disorder ADHD

ADHD is believed to be caused by several genetic and environmental factors. Most of the research on causation factors, suggests that ADHD is caused by environmental factors including perinatal stress, smoking, and alcohol use during pregnancy, environmental toxins such as lead exposure, and nutrient deficiencies. Different studies have suggested that maternal body mass index (BMI) and obesity, before and during pregnancy are linked to the risk of developing ADHD. Genetic causation has been found in studies that discovered a link between parents with ADHD and their children (e.g., Tandon & Pergjika, 2017).

The ADHD Gut Connection

One particular causation factor which has increased the interest of researchers more recently is the role of gut bacteria in Attention Deficit Hyperactivity Disorder. ADHD has been found to have a much higher prevalence in patients with gastrointestinal complaints (Kedem, et. al., 2020). The relationship between ADHD and gut issues may be more complex than just causation alone.

The gut has a complex network of neurons that is referred to as the Enteric Nervous System or the second brain. Several mental health conditions such as autism spectrum disorder, depression, bipolar disorder, and anxiety disorders are all found to be related to gut health issues (Aizawa, et al., 2019).

While some research has found that ADHD and gut health issues are correlated, other research has found that ADHD has a major direct impact on the gut. In contrast, other research has found that gut issues may play a role in the causation of ADHD, or ADHD symptoms (Ming, et. al., 2018).

One explanation of the ADHD-gut connection is that ADHD disrupts gut bacteria, which in turn affects mood and executive functioning (Pierce & Alvina, 2019). ADHD patients have been found to have an imbalance in their gut microbes, with higher levels of harmful bacteria and lower levels of good bacteria.

Evidence also proposes that food allergies in children and adults are associated with behavioral problems and neuropsychiatric disorders, including ADHD. ADHD patients also have an increase in the incidence of leaky gut, which is linked to other mental health conditions such as anxiety and depression. ADHD patients have also been found to suffer from gastrointestinal disturbances such as irritable bowel syndrome (IBS), constipation, and diarrhoea more often than those without ADHD (Kohane et al., 2012).

Gut microbiota and neurodevelopment: The Gut-Brain Axis

The gut-brain axis theory proposes that the gut microbiome could influence brain function in multiple ways. The relationship between the digestive microbiome and its host is bidirectional. Simply, the brain and the gut talk to each other. The gut talks to the brain through a nerve pathway, a hormone pathway, and the immune system. This is called the MGBA - Microbiota-Gut-Brain Axis. The gut microbiome communicates with the central nervous system through hormonal, immune, and innate neuronal pathways.

The MGBA's role in ADHD is not very clear. Some research attributes it to the composition and number of microorganisms that infiltrate the digestive tract through the food system, health conditions, and lifestyle. As the modern lifestyle has caused a huge impact on the digestive health microbiome, the incidence of ADHD has increased.

In a Taiwanese study, the team around Wang et al. (2019) compared fecal microbiota compositions and found that people with ADHD had a different level of bacteria in their stool. ADHD patients had a higher percentage of the bacterium Enterobacter in their stools compared to healthy controls, which reveals that ADHD patients have a different gut microbiome.

Gut issues, mood disorders, and ADHD Symptoms

A variety of other neurological and neurodevelopmental disorders, such as multiple sclerosis, Alzheimer's, Parkinson's, autism spectrum disorders (ASD) as well as attention deficit hyperactivity disorder (ADHD) have been associated with an imbalance in the gut microbiome composition. 

ADHD is also associated with several other mental health conditions which also are related to gut health issues. Several studies have found that people with ADHD are more likely to experience mood disorders such as bipolar and major depressive disorder (e.g., Peirce & Alviña, 2019).

People with ADHD often have a more heightened sensitivity to stress in comparison to the general population, due to common challenges with mood regulation and overall difficulty with cognitive functions. The immune system response to stress is often through inflammation. Inflammation can disrupt the gut microbiome, resulting in several stomach issues, including irritable bowel syndrome and food sensitivities. People with ADHD often experience gastrointestinal issues throughout life (Kedem, et al., 2020).

The gut microbiome has been found to have a major impact on mood, as it is responsible for producing important neurotransmitters. Specifically, gut microbiota alterations have been found to contribute to the abnormal metabolism of dopamine and norepinephrine, which are responsible for ADHD symptoms (Strandwitz, 2019).

ADHD symptoms: Impact of gut health on mood, concentration, and executive functioning

As we have established, gut health is directly linked to ADHD symptoms through the gut microbiome. The gut-brain axis system impacts ADHD brain functioning, mood regulation and, executive functioning. It is thought this is due to inflammation of the intestinal tract which leads to disruption of neurotransmitter functions that aid cognitive abilities such as focus and concentration. Norepinephrine and dopamine regulation are commonly associated with ADHD symptoms such as distraction, impulsivity and hyperactivity (Strandwitz, 2019).

ADHD symptoms such as mood and irritability have been found to also be influenced by gut health. Further, people with ADHD that have gastrointestinal issues tend to experience higher levels of difficulty with emotion regulation. Gut health issues also contribute to a child's behavioral temperament, including emotional reactivity and mood disorders. ADHD symptoms such as ADHD hyperactivity and impulsivity can be exacerbated by gut conditions such as irritable bowel syndrome (IBS).

The Impact of ADHD Medication on Gut Health

Stimulants such as methylphenidate hydrochloride, which are used broadly as first-line therapies for ADHD, target the reuptake of noradrenaline and dopamine. Psychostimulants, and methylphenidate (MPH) in particular, represent the first-line medication for moderate and severe cases of ADHD in children from 5 years and over and young patients. However, the long-term use of ADHD stimulants is still debated.

ADHD medications are taken orally, usually once daily in the morning (usually after breakfast), are often initially helpful to regulate ADHD symptoms, but can be associated with adverse effects. There are limited and inconclusive findings to suggest that stimulants may upset the human gut microbial composition. Kedem and colleagues' 2020 study lent some weight to the possibility that methylphenidate use was associated with an increased risk of stomach pains and constipation but not associated with leaky gut or celiac disease.

Gut health interventions

Helpful bacteria for gut microbiota composition

Some studies have shown the protective effects of healthy bacterias for ADHD (Checa-Ros, et al., 2021). Research shows there are now several natural supplements, such as probiotics and prebiotic fibers which can help improve intestinal flora diversity in people with ADHD. These may aid treatment for ADHD by alleviating gastrointestinal symptoms by building healthy gut microbiota, in response to the abundant build-up of Bifidobacterium (Kumperscak, et al., 2020).

Micronutrient supplementation has been found to assist with healthy gut microbiota and in turn, help with regulating ADHD symptoms such as mood and irritability (Lange, 2020). Specifically, Omega 3 polyunsaturated fatty acids (PFA's) are somewhat helpful for ADHD symptoms. However, rather than focusing on one type of micronutrient, it is recommended to identify a whole diet approach and healthy lifestyle approach.

Foods to support healthy human microbiota and ADHD

Many of the Omega 3's are found in fish oils, uncooked olive oil, avocados and other types of PFA'S have been part of a whole diet approach to increasing healthy gut bacteria. Diets such as the Mediterannean eating plan have been researched as potential support for managing ADHD symptoms (Lange, 2020). In addition, a 2017 study by Rios-Hernandez and colleagues found a significant difference in the reduction of ADHD symptoms in those who followed the Mediterranean diet.

Other environmental interventions for Gut Health and ADHD

Apart from the food we consume, it is also important to account for other elements in our environment which can cause oxidative stress. Oxidative stress is caused by everything we consume in our environment including pesticides, pollution, stress, smoking, alcoholism and, radiation exposure. Research has found that oxidative stress is linked to gut health and ADHD (e.g., Joseph, et al., 2013). Reducing the impact of oxidative stress is essential, both through diet and other health interventions such as exercise and stress reduction techniques.


Overall, the impacts of gut health on ADHD symptoms are important to consider. It remains somewhat of a mystery about which comes first, whether the microbiome system influences ADHD, or whether ADHD impacts the gut micro-organisms. Much of the research has established that ADHD can hurt gut health and vice versa. Perhaps the ADHD brain-gut link can be best understood in how the nervous system, hormones, and the immune system are impacted by gut microbiota and how this impacts neurotransmitter development and function. To protect and ensure healthy neurodevelopment, it is essential to consider everything we consume from food to environmental conditions and the whole internal and external ecosystems' impact on the gut-brain connection.


Shannon Bowman is the director of SJB Clinical Consulting Pty Ltd
And Director of Create Balance Psychotherapy & Counselling VIEW HERE.
Shannon has a clinical interest in treating trauma, PTSD and ADHD.
He has a lived experience of ADHD and is a passionate advocate for those affected by it.
He is accredited as a Mental Health Social Worker AMHSW,
psychotherapist and registered EMDR practitioner. Associations below. 
Australian Association of Social Workers
EMDR Association of Australia.
Psychology Today Profile

Daniel Van der Pluym is a Psychotherapist Coach
Founder of Deeper Potential and Part Founder of ADHD Ambition Daniel specialises in Mindfulness as a way of regulating difficult thoughts and feelings and supporting people's mental wellbeing through a holistic approach.
He has a lived experience of anxiety, inattention and difficulty focusing and is passionate about helping those who experience similar challenges.
He is an Associate Member of the Australian Psychological Society and Member of Meditation Australia


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