If you have attention deficit hyperactivity disorder (ADHD), you know how challenging it can be to stay focused, regulate your emotions, and manage your energy levels and responsibilities throughout the day. While factors like your diet, lifestyle, and genetics can influence your susceptibility to ADHD symptoms, did you know that histamine and ADHD are connected?
Histamine is a chemical best known for its role in allergic reactions, but its role in ADHD is just now beginning to be understood.
Histamine isn’t just about sneezing and seasonal allergies—it’s also a key neurotransmitter that influences brain function, focus, mood, and even sleep. And when histamine levels aren’t properly regulated, it can contribute to brain fog, hyperactivity, and difficulty concentrating.
In this article, we’ll dive into the connection between histamine and ADHD1, explore the role of the diamine oxidase (DAO) enzyme in histamine sensitivity, and discuss how histamine intolerance may be making your ADHD symptoms worse. Plus, we’ll cover strategies to help manage histamine sensitivity and improve focus naturally.
In this article:
What Is Histamine?
Histamine is a neurotransmitter and immune system messenger2. It's involved in digestion, inflammation, immune response, and brain function. While most people associate histamine with allergies, it also affects the nervous system3, influencing cognitive processes including alertness, wakefulness, and attention.
Effects of Histamine Include:
Neurological Effects
- Acts as a neurotransmitter, influencing wakefulness and alertness
- Plays a role in attention, learning, and memory
- Can contribute to hyperactivity and impulsivity (potential ADHD link)
- May cause brain fog and difficulty concentrating when levels are imbalanced
- Triggers headaches and migraines in sensitive individuals
- Involved in autism spectrum disorder
- Increased attention-deficit/hyperactivity symptoms
Immune System & Inflammation
- Key player in allergic reactions (allergic symptoms like itching, swelling, hives)
- Food allergy and reactions to foods
- Increases inflammation and can worsen autoimmune conditions
- Triggers the release of stomach acid, potentially causing acid reflux
- Can contribute to histamine intolerance symptoms like flushing and nasal congestion
Cardiovascular Effects
- Dilates blood vessels, leading to low blood pressure and dizziness
- Can cause rapid heart rate (tachycardia)
- May contribute to palpitations in histamine-sensitive individuals
Gastrointestinal Effects
- Increases stomach acid production, which can cause indigestion or ulcers
- Affects gut motility, leading to diarrhea or bloating
- Can contribute to food sensitivities and gut inflammation
Sleep & Mood Effects
- Regulates the sleep-wake cycle; high levels can cause insomnia and sleep disorders
- Low histamine may contribute to fatigue and drowsiness
- Linked to mood disorders like anxiety and irritability
Histamine is broken down by the diamine oxidase (DAO) enzyme, which helps regulate its levels in the body. When histamine builds up due to a DAO enzyme deficiency, it can lead to histamine intolerance—a condition linked to symptoms including headaches, brain fog, and digestive distress.
What Is ADHD?
Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder or condition that affects focus, impulse control, and executive function deficit. ADHD can look different in different people—and ADHD symptoms are often unique in women compared to men.
ADHD is characterized by:
- Inattention (difficulty focusing, forgetfulness, disorganization)
- Hyperactivity (restlessness, difficulty sitting still, excessive energy)
- Impulsivity (acting without thinking, interrupting conversations, poor decision-making)
Many people with ADHD also experience sensory sensitivities, mood swings, PMDD, and sleep disturbances, such as due to the link between ADHD and hormones. Among women with ADHD, other symptoms can include forgetting where things are, having trouble managing their schedule, and having relationship issues.Related: ADHD and PMDD Hormone Connection and ADHD Types and Hormones: The Unexpected Link You Need to Know
The Role of Histamine in ADHD
While ADHD is often linked to dopamine and norepinephrine imbalances, histamine is another factor that can contribute to ADHD symptoms by disrupting attention and brain function. In fact, emerging research4 suggests there can be a strong connection between histamine and ADHD, as well as other psychiatric conditions, including Alzheimer’s disease, Parkinson’s disease, and schizophrenia.
Histamine is known to affect the central nervous system5, influencing neuron activity, wakefulness, focus, and neurotransmitter balance—so it makes sense that high histamine can also contribute to ADHD symptoms increasing in some people.
In one study6, researchers examined whether allergies, anemia, inflammation, and neurotransmitter levels contribute to ADHD risk. Researchers found that when children with ADHD were compared to controls they were more likely to have:
- signs of allergies (like atopic dermatitis or eczema and rhinitis)
- lower hemoglobin and serotonin levels
- higher IgE levels and eosinophil counts (markers of immune system activity, particularly related to allergic reactions and inflammation)
The risk of ADHD increased as more of these factors were present, suggesting that ADHD can have multidimensional causes and shared underlying factors with these conditions.
Similarly, another study7 found that children with high urinary histamine levels had increased inattention compared to those with normal histamine levels.
Here's more about the key ways that histamine impacts ADHD:
1. Histamine Regulates Dopamine and Acetylcholine Levels
Elevated histamine can lead to dysregulation of dopamine and acetylcholine neurotransmitters, which can further compromise executive function.
Dopamine is a neurotransmitter that plays a crucial role in motivation, pleasure, and focus—areas where people with ADHD often struggle. Acetylcholine, on the other hand, supports learning, memory, and attention.
Too much histamine in the brain can disrupt the balance of these neurotransmitters, leading to heightened distractibility, poor memory retention, and difficulties in maintaining focus.
When histamine levels are too high, dopamine function can become dysregulated, potentially leading to mood swings, hyperactivity, and impulsivity—all of which are hallmarks of ADHD.
Similarly, disruptions in acetylcholine levels can impact working memory and executive function, making it harder to plan, make decisions, and organize tasks.
2. Histamine Intolerance Can Mimic or Worsen ADHD symptoms
Histamine intolerance occurs when the body struggles to break down excess histamine due to a deficiency in the diamine oxidase (DAO) enzyme. This can cause a buildup of histamine, leading to symptoms that closely resemble or intensify ADHD symptoms, including:
- Brain fog: Difficulty thinking clearly or processing information, or feelings of fatigue
- Inattention: Struggling to focus for extended periods
- Anxiety: Heightened restlessness or nervousness, and often trouble sleeping
- Irritability: Increased emotional sensitivity or mood swings
3. Histamine Often Influences Sleep
Sleep disturbances are extremely common in ADHD, with many people experiencing difficulty falling asleep, staying asleep, or waking up feeling unrefreshed.
Histamine plays a key role in regulating wakefulness, and histamine imbalances can disrupt sleep cycles, making ADHD symptoms even harder to manage, such as by causing moodiness and irritability during the day.
Too much histamine in the brain can lead to insomnia and restlessness at night. On the other hand, too little histamine may contribute to daytime drowsiness and fatigue, making it difficult to stay engaged and focused. Since poor sleep can worsen focus, impulsivity, and mood, addressing histamine balance is key for improving sleep quality and overall ADHD management.
4. Antihistamines Can Impact ADHD Symptoms
For those wondering, “Can antihistamines make ADHD worse?”—it depends on the type of antihistamine. Some may disrupt neurotransmitter balance8, while others can potentially help with ADHD symptoms.
Antihistamines, commonly used to treat allergies, can affect ADHD symptoms in different ways depending on the type:
- Sedating antihistamines (like Benadryl): These can increase drowsiness and worsen brain fog, making it harder to stay alert and focused. Benadryl is also no longer recommended for the treatment of histamine issues since long-term use has been linked to an increased risk of dementia and cognitive decline. Plus Benadryl can lead to hallucinations, seizures, breathing difficulties and heart issues.
- Non-sedating antihistamines (like Claritin or Zyrtec): While these may not cause sleepiness, they can still alter neurotransmitter activity, potentially affecting focus and motivation.
So regarding whether or not antihistamines make ADHD worse, the answer varies depending on the individual and the specific antihistamine used. If you take antihistamines and notice worsening ADHD symptoms, consider discussing alternatives with your healthcare provider.
Benadryl and ADHD content is all over social media touting the benefits in reducing ADHD symptoms. I caution people from using benadryl and ADHD due to the potential for worsening neurological effects. If you’re considering using antihistamines for ADHD, discuss Claritin or Zyrtec with your provider and if H2 blockers like Pepcid should be part of the protocol.
Related: This Is How Your ADHD Can Affect You During Menopause
What Is the Diamine Oxidase (DAO) Enzyme and Why Does It Matter?
As mentioned above, the enzyme called diamine oxidase (DAO) is responsible for breaking down excess histamine. A DAO enzyme deficiency can lead to excess histamine, triggering symptoms that overlap with ADHD9, such as brain fog, irritability, and hyperactivity.
Some people have a genetic predisposition to low DAO levels, leading to a higher likelihood of having histamine intolerance. This condition is thought to affect about 1% of the general population10.
Some studies suggest that children and adults with ADHD may have lower DAO enzyme activity, leading to histamine accumulation.
Diamine oxidase DAO deficiency symptoms can include headaches, gut issues, skin reactions, and fatigue. If you have ADHD and experience these symptoms, supporting DAO enzyme activity may help.
Diamine Oxidase Deficiency Symptoms:
- Brain fog, difficulty concentrating
- Hyperactivity, restlessness
- Mood swings, irritability
- Headaches or migraines
- Digestive issues (bloating, diarrhea)
- Skin reactions (hives, itching)
Signs and Symptoms of Histamine Intolerance
Histamine intolerance occurs when the body cannot properly break down histamine, leading to a buildup of histamine in the system. Many people with ADHD may not realize that histamine intolerance is contributing to their focus and mood challenges.
Common symptoms of histamine intolerance or sensitivity can include:
- Neurological symptoms: Brain fog, anxiety, dizziness, headaches, and migraines
- Digestive issues: Bloating, diarrhea, nausea, or acid reflux
- Skin reactions: Hives, itching, or flushing
- Cardiovascular symptoms: Rapid heartbeat or low blood pressure after eating certain foods
- Respiratory symptoms: Congestion, sneezing, or asthma-like symptoms
Managing Histamine Intolerance and ADHD
If you suspect you may have histamine intolerance and ADHD, there are a number of ways to help manage your symptoms, including approaches that help reduce histamine exposure, improve histamine metabolism, and support neurotransmitter balance:
1. Limit or Avoid High-Histamine Foods
Certain foods naturally contain high levels of histamine or trigger histamine release in the body. Avoiding or minimizing these foods11 may help reduce symptoms:
- Eliminate aged and fermented foods, such as aged cheeses, cured meats, sauerkraut, and kimchi.
- Limit alcohol consumption, especially wine, beer, and champagne, which are high in histamine.
- Eat fresh, whole foods that rather processed ones with artificial additives, colors, dyes, and synthetic ingredients.
- Be mindful of nuts. If you're wondering, are nuts high in histamine, the answer is that some nuts, like walnuts and cashews, may trigger histamine responses more than others. This depends on the person, so it can take some trial and error to determine if you're sensitive to certain nuts or not.
- Opt for fresh meats and vegetables rather than processed or leftover foods, as histamine levels increase with storage time.
You can also find out more about ADHD treatments for women here: ADHD in Women: Symptoms, Causes, and Treatment
2. Support DAO Enzyme Activity
As you learned above, the diamine oxidase (DAO) enzyme is responsible for breaking down histamine in the gut. If DAO activity is low, histamine builds up and causes symptoms. Boosting DAO function can help, and these steps can often do that:
- Consume DAO-supporting foods, such as grass-fed meat, wild-caught fish, and pasture-raised eggs.
- Increase vitamin B6 (found in my Balance Women's Hormone Support formula) and copper intake, as these nutrients help activate DAO.
- Try DAO supplements before meals to help break down dietary histamine.
- Avoid foods that block DAO activity, such as alcohol and processed foods.
- Speak to your provider about psychostimulant medications that can help regulate DAO12, depending on the person and situation.
3. Optimize Your Gut Health
Since histamine is largely metabolized in the gut, probiotics, digestive enzymes, and a balanced microbiome may be able to help gut health and manage symptoms.
Probiotics can be especially helpful because they've been shown to help with histamine intolerance and ADHD by supporting gut health and neurotransmitter balance and breaking down histamine.
For histamine intolerance, low-histamine probiotics, such as Lactobacillus rhamnosus, Bifidobacterium infantis, and Bifidobacterium longum, can promote histamine degradation and reduce inflammation. These strains also support dopamine and acetylcholine production, which are essential for focus, learning, and impulse control in individuals with ADHD.
Additionally, a healthy gut microbiome helps regulate the gut-brain axis, improving mood stability, reducing hyperactivity, and enhancing cognitive function.
- Incorporate gut-friendly probiotics into your diet and supplement routine, and ideally choose low-histamine strains like Lactobacillus rhamnosus and Bifidobacterium infantis. In my Women's Probiotic, you'll find a blend of probiotics (including those in the Lactobacillus family), prebiotics, and antioxidants designed to specifically support healthy hormones.
- Add prebiotics to your diet, which help probiotics to thrive, such as high-fiber foods like greens, artichokes, whole grains, bananas, nuts, and seeds.
- Use digestive enzymes that help break down histamine-containing foods, taking stress off of the gut.
- Reduce common gut irritants, such as processed foods, sugar, alcohol, artificial additives, and unnecessary medications.
- Support the integrity of your gut lining with help from supplements and foods that can help, such as collagen peptides, bone broth, and L-glutamine.
4. Balance Neurotransmitters
Since histamine interacts with dopamine and acetylcholine, optimizing neurotransmitter balance can often help improve focus, energy, sleep, mood stabilization, and mental clarity.
- Get enough sleep, aiming for 7 to 9 hours each night.
- Spend time in nature and get sunlight exposure during the daytime, which can lift your energy and mood and assist in sleep.
- Do things that you find uplifting and relaxing each day, like reading, journaling, socializing, art, learning new things, etc.—all of which can help release “feel food” neurotransmitters.
- Use adaptogenic herbs, such as ashwagandha or Rhodiola, to support cognitive function and stress resilience. You'll find these in my Adrenal Support formula, which is also beneficial for boosting resilience to stress, sleep, and mood regulation.
- Support dopamine production by consuming tyrosine-rich foods, such as eggs, beef, and fish.
- Boost acetylcholine levels with dietary sources like eggs, sunflower lecithin, and choline supplements.
- Engage in regular exercise, which naturally supports neurotransmitter regulation.
Related: Exploring Natural Solutions for Adult ADHD — How To Find Relief
Be Mindful of Medications
Some medications, including certain antihistamines and ADHD medications, can interfere with histamine metabolism. If you're taking allergy or ADHD medications, consider these factors:
- Sedating antihistamines (like Benadryl) can increase drowsiness and worsen brain fog, which may impact ADHD symptoms. Ask yourself if these meds are impacting your ability to work and focus during the day.
- Non-sedating antihistamines may still affect neurotransmitter activity, potentially contributing to mood-related issues and energy crashes.
- Discuss medication options with your doctor if you suspect histamine intolerance is contributing to ADHD-related issues.
Final Thoughts on ADHD and Histamine
- Brain fog, difficulty concentrating, and anxiety—common in histamine sensitivity—overlap with ADHD symptoms. Yet many people may not realize that histamine intolerance is contributing to their cognitive difficulties.
- If you struggle with ADHD and histamine intolerance, addressing histamine metabolism may improve focus, energy, and overall well-being.
- Supporting DAO enzyme activity, avoiding high-histamine foods, and balancing neurotransmitters are key strategies for optimizing brain function.
- If histamine sensitivity is affecting your ADHD, working with a healthcare provider to tailor a treatment plan is the best approach.
References
- https://www.mdpi.com/2077-0383/12/16/5350 ↩︎
- https://medlineplus.gov/medlineplus-videos/histamine-the-stuff-allergies-are-made-of/ ↩︎
- https://linkinghub.elsevier.com/retrieve/pii/S0014-2999(06)01320-3 ↩︎
- https://www.medcentral.com/behavioral-mental/adhd/histamine-and-psychiatric-disorders ↩︎
- https://www.sciencedirect.com/science/article/abs/pii/S0896627324008808 ↩︎
- https://www.nature.com/articles/s41598-018-28702-5 ↩︎
- https://link.springer.com/article/10.1007/s41252-024-00432-y ↩︎
- https://www.mdpi.com/2077-0383/12/14/4666 ↩︎
- https://www.mdpi.com/2077-0383/12/16/5350 ↩︎
- https://www.medcentral.com/behavioral-mental/adhd/histamine-and-psychiatric-disorders ↩︎
- https://psychiatryonline.org/doi/10.1176/appi.ajp.2010.09101529 ↩︎
- https://www.mdpi.com/2077-0383/12/14/4666 ↩︎
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