What Do ADHD and MCAS Have in Common?
Attention-deficit/hyperactivity disorder (ADHD) affects approximately 11% of children and 6% of adults, while mast cell activation syndrome (MCAS) is estimated to impact up to 17% of the population—yet it remains largely underdiagnosed.
Interestingly, a growing number of people are reporting overlapping symptoms or even co-occurring diagnoses of ADHD and MCAS. Is there a biological connection? Or is the symptom overlap simply coincidental?
Let’s explore what we know so far.
What Is MCAS?
MCAS is a chronic condition in which mast cells—a type of immune cell involved in inflammatory responses—become overly reactive. These cells release a range of chemical mediators, such as histamine, prostaglandins, leukotrienes, and cytokines.
This leads to symptoms that can impact nearly every system in the body, such as:
Brain fog
Fatigue
Headaches
Digestive issues
Itchy or sensitive skin
Cardiovascular symptoms
Respiratory discomfort
What Is ADHD?
ADHD is a neurodevelopmental condition that affects executive function—how the brain regulates attention, motivation, activity level, and impulse control.
Common symptoms include:
Difficulty concentrating
Restlessness or hyperactivity
Emotional dysregulation
Trouble with organization and time management
Mental fatigue or overwhelm
Sensory sensitivities
While ADHD is traditionally thought of as a brain-based disorder, newer research increasingly links it to immune dysregulation and inflammation as well.
Shared and Overlapping Symptoms
Many individuals with MCAS or ADHD experience similar challenges, making it hard to differentiate between the two—or recognize when both are present. Here are some common overlaps:
Fatigue
MCAS: Immune system over-activation can drain energy reserves. ADHD: Mental effort required to focus or regulate emotions can cause exhaustion.
Sensory Sensitivities
Heightened reactions to light, sound, touch, smell, or temperature. Can lead to sensory overload, irritability, or withdrawal.
Brain Fog
Slowed processing, trouble recalling words, or mental fuzziness.
Mood Dysregulation
Emotional reactivity, irritability, overwhelm. Often mistaken for mood disorders in both conditions.
These overlapping symptoms can create confusion, particularly in clinical settings where one condition may be diagnosed while the other is missed entirely.
The Role of Mast Cells in Neuroinflammation
Neuroinflammation refers to inflammation in the brain or central nervous system—and mast cells play a key role in this process. When activated, mast cells release mediators that can cross or impact the blood-brain barrier, influencing brain function and mood.
Mast cell-related neuroinflammation has been linked to several other neurological and psychiatric conditions through research, including:
Multiple sclerosis (MS)
Autism spectrum disorder (ASD)
Depression
Post-traumatic stress disorder (PTSD)
Chronic pain and migraine
This raises an important question: Could mast cells be contributing to the inflammation seen in ADHD, too?
What Does the Research Say?
Although the science is still emerging, recent studies suggest a possible role of mast cells in ADHD. Some research has linked ADHD to general inflammation and immune activation—but specific evidence connecting MCAS or mast cells to ADHD is still developing. The exact biological mechanisms remain unclear, and more research is needed before any conclusions can be drawn.
ADHD and MCAS: Co-Occurrence or Confusion?
It’s entirely possible that MCAS and ADHD co-occur in some individuals, particularly those with overlapping conditions like:
Postural orthostatic tachycardia syndrome (POTS)
Ehlers-Danlos syndrome (EDS) or hypermobility spectrum disorder (HSD)
Autoimmune or neuroimmune conditions
Because both MCAS and ADHD can affect energy, cognition, and emotional regulation, it can be difficult to know which condition is driving which symptoms—or whether they are feeding into each other.
While MCAS is not yet officially recognized as a cause of ADHD, the potential link through neuroinflammation and immune system dysfunction is gaining more attention. If you or a loved one have been diagnosed with ADHD but also experience unexplained physical symptoms (like allergic-type reactions, food sensitivities, or chronic fatigue), it may be worth learning more about MCAS.
Awareness is the first step toward more personalized treatment and support. As research evolves, so will our understanding of how these two complex conditions may be connected.
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PMID: 32742317; PMID: 38003876; PMID: 37629392; CDC: Data and Statistics on ADHD (2024); CDC: Facts About ADHD in Adults (2024)
Disclaimer: This blog post is for informational purposes only and shall not be construed as behavioral health or medical advice. It is not intended or implied to supplement or replace treatment, advice, and/or diagnosis from your own qualified healthcare provider.