Brain Fog and ADHD

Does your brain sometimes feel like it's wrapped in cotton wool? You know you're capable of clear thinking, you've done it before, but lately, your thoughts move through thick haze.

It shows up everywhere. You're staring at your screen, reading the same paragraph three times, and it still doesn't register. Simple decisions suddenly feel overwhelming. Someone asks you a question and your mind goes blank. By mid-afternoon, the thinking itself feels exhausting.

If you have ADHD, this might feel familiar, maybe even inevitable. But there's something important the research shows: this experience, commonly called "brain fog," isn't actually part of ADHD itself. It's a signal pointing to something else: sleep problems, mood issues, hormonal shifts, medication effects, or other medical factors. And once you understand what's causing it, you can work on addressing it.

So let's start with the basics: what brain fog actually is, what science knows (and doesn't know) about it, and how to figure out what's driving yours.

What Is "Brain Fog"? (And What It Isn't)

Brain Fog Is a Real Experience With No Official Diagnosis

"Brain fog" is the term people reach for when they're trying to describe something that feels hard to pin down: their thinking has become cloudy, confused, or slow. They're struggling to concentrate, forgetting things more than usual, feeling mentally "spacey".

The challenge is that brain fog isn't a medical diagnosis. You won't find it in diagnostic manuals, and there's no blood test or brain scan that can detect it. Doctors don't have a standardised definition they all agree on. What brain fog actually is, in the research, is a "lay term": everyday language that people use to describe their subjective experience of impaired cognition.

Think of it like saying you have a stomach ache. That's a real feeling, and it matters, but it doesn't tell your doctor what's actually wrong. It could be hunger, stress, food poisoning, appendicitis, or dozens of other things. Brain fog works the same way, it's a real experience pointing toward an underlying cause that needs investigation

What We Know About Brain Fog

Research over the past few years (especially since COVID-19 brought brain fog into mainstream conversation) has revealed several important things:

1. Brain fog is remarkably common across many different conditions

Brain fog is reported across many medical and psychological conditions, including:

Long COVID and post-viral syndromes
Menopause and hormonal transitions
Depression and anxiety
Sleep disorders (insomnia, sleep apnea, delayed sleep phase)
Chronic fatigue syndrome
Fibromyalgia
Autoimmune conditions (lupus, MS)
Thyroid disorders
Chemotherapy ("chemo brain")
Nutritional deficiencies (iron, B12, vitamin D)
Medication side effects
And yes, it's commonly reported by people with ADHD

Key point: Brain fog is not specific to any one condition. It's a shared symptom across very different causes.

2. Brain fog describes overlapping symptoms in four main areas

When researchers analyse what people mean by "brain fog," they find it involves:

Attention problems: Difficulty concentrating, easily distracted, zoning out
Memory difficulties: Forgetfulness, losing train of thought, word-finding problems
Slowed processing: Thinking feels slower, taking longer to understand or respond
Mental fatigue: Feeling mentally exhausted, even simple thinking requires effort

Often these come with emotional and physical components too—mood changes, physical tiredness, feeling overwhelmed.

3. Brain fog is subjective and doesn't always match objective testing

Here's something fascinating: Research shows that brain fog is related to, but separate from, actual cognitive performance on tests.

What does that mean? Someone can feel extremely foggy but perform normally on memory tests and attention tasks. Conversely, someone might have measurable cognitive deficits but not experience the subjective feeling of "fog."

This doesn't mean brain fog is "all in your head" or not real. It means that:

The subjective feeling of cognitive difficulty is a real phenomenon worth taking seriously
It can be influenced by factors beyond just cognitive performance (like fatigue, anxiety, mood)
Fixing the fog often requires addressing these interconnected factors

4. Different conditions likely cause brain fog through different mechanisms

Recent research suggests that rather than one "brain fog syndrome," there are probably multiple types of brain fog with different underlying causes:

Inflammation-related fog (post-viral, autoimmune conditions): Possibly caused by immune system effects on the brain
Hormone-related fog (menopause, thyroid): Linked to hormonal effects on neurotransmitters
Sleep-deprivation fog: Caused by inadequate rest and impaired brain waste clearance
Mood-related fog (depression, anxiety): Mental resources consumed by emotional processing
Arousal-dysregulation fog (some ADHD presentations): Problems with brain activation and alertness states

We're still learning how to distinguish these types, but the key insight is: brain fog is a symptom, not a disease. Just like "fever" can come from the flu, an infection, or heat stroke, "brain fog" can come from many different sources.

What We Don't Know Yet

Scientific understanding of brain fog is still developing. Major gaps include:

No standardised way to measure it: We don't have a "brain fog test" or agreed-upon scale
Unclear mechanisms in many conditions: We're still figuring out exactly what's happening in the brain
Limited treatment studies: Most research focuses on the underlying conditions, not "fog" specifically
Individual variation: Why some people with a condition get brain fog and others don't is often unclear

Researchers are actively working on these questions, especially after the COVID-19 pandemic brought renewed attention to cognitive symptoms.

Brain Fog and ADHD: What Research Shows

Now let's get specific about ADHD. If you have ADHD and experience brain fog, what does the science say?

ADHD Itself Isn't Characterised by "Brain Fog" as a Core Symptom

According to the DSM-5-TR, ADHD is defined by persistent patterns of inattention, distractibility, and/or hyperactivity-impulsivity that started in childhood. The cognitive features of ADHD include:

Difficulty sustaining attention on tasks
Easy distractibility by external stimuli or internal thoughts
Working memory challenges (trouble holding information in mind)
Executive function difficulties (planning, organising, initiating tasks)
Sometimes slowed processing speed during complex multitasking

These are real cognitive difficulties, and they're part of the ADHD neurodevelopmental pattern.

But here's the distinction: These features are typically consistent traits you've had over time, not an episodic "fog" that comes and goes. ADHD symptoms might fluctuate with stress or environment, but the underlying pattern is chronic.

"Brain fog," in contrast, is usually described as:

Episodic (comes and goes, has good days and bad days)
A change from your baseline (you feel "not yourself")
Mental heaviness or sluggishness beyond your usual ADHD challenges

Why Many People With ADHD Experience Brain Fog

If brain fog isn't a core part of ADHD itself, why do so many adults with ADHD report it?

Because adults with ADHD have very high rates of conditions that are likely related to brain fog. Additionally, some specific ADHD-related experiences (like Sluggish Cognitive Tempo, discussed below) can contribute to foggy feelings.

1. Sleep Problems (Common in Adults with ADHD)

Evidence strength: Strong

This is likely the biggest driver of brain fog in the ADHD population.

The overlap is striking:

Sleep problems are very common in adults with ADHD (estimates vary by study and definition; around 60% may screen positive for a sleep disorder in clinical samples, with insomnia symptoms reported in 30-80% across different studies)
Adults with ADHD are far more likely to have delayed sleep phase syndrome (night owl patterns), sleep apnea, and non-refreshing sleep
Sleep deprivation directly causes attention problems, memory impairment, slowed processing, and mental fatigue
These symptoms look almost identical to "brain fog"

What the research shows:

Chronic inadequate sleep "compounds the cognitive problems" in ADHD
Sleep deprivation directly causes attention problems, memory impairment, slowed processing, and mental fatigue
Sleep disruption impairs multiple restorative processes (including memory consolidation and brain-fluid dynamics). The exact role of glymphatic "waste clearance" in humans is still being debated
Sleep-disordered breathing (like sleep apnea) causes significant cognitive impairment due to nighttime oxygen drops
Treating underlying sleep disorders and sleep pattern disruptions can "reverse a source of cognitive impairments" in people with ADHD

Translation: If you have untreated sleep problems, no amount of ADHD medication will fully clear the fog. Your brain is literally sleep-deprived.

The problem: Sleep issues in ADHD is an emerging research area. Many people don't realise their sleep is the issue.

2. Anxiety and Depression (Common Comorbidities)

Evidence strength: Strong (especially for subjective complaints)

Here's a crucial research finding: Across mental health conditions, subjective "brain fog" complaints are often more strongly associated with sleep quality and anxiety/depression severity than with objective cognitive test performance.

Research in adults with ADHD has found that when people report feeling mentally foggy, those complaints are strongly tied to mood and anxiety symptoms, sometimes more so than to performance on cognitive tests or ADHD symptom severity.

What this means:

Depression directly causes concentration problems, mental slowing, and memory difficulties
Anxiety consumes mental bandwidth (your brain is busy worrying, leaving fewer resources for everything else)
These cognitive effects of mood disorders feel like "brain fog"

Why it matters: You might be trying to optimise your ADHD treatment when the real issue is untreated depression or anxiety. Addressing the mood disorder might clear the fog more effectively than adjusting your ADHD medication.

3. Hormonal Changes (Particularly for Women)

Evidence strength: Moderate/Emerging

Many women with ADHD report that cognitive symptoms dramatically worsen during:

The premenstrual phase of their cycle
Postpartum period
Perimenopause and menopause

The science: Oestrogen has modulatory effects on dopamine activity in the brain. When Oestrogen drops (before menstruation, after childbirth, during menopause), dopamine signalling can weaken. Since ADHD already involves dysregulated dopamine function, these hormonal shifts can compound existing cognitive difficulties.

What women report:

Stimulant medications become less effective
Memory and word-finding problems increase
Mental clarity decreases
Concentration and focus become noticeably harder
Task initiation requires more effort
Mental processing slows down
Mental fatigue sets in earlier in the day
Classic "foggy" or "hazy" feeling intensifies

The research is still developing, but clinical observations are consistent: hormonal transitions can trigger significant cognitive challenges in women with ADHD, consistent with brain fog, beyond their baseline ADHD symptoms.

4. Medication Effects

Sometimes the brain fog is actually a side effect, rather than a symptom you're trying to treat:

ADHD medications themselves:

Wrong medication type (stimulant vs. non-stimulant may affect you differently)
Incorrect dose: too high can cause jitteriness, mental fog, or a "zombie" feeling; too low may leave symptoms undertreated
Poor timing (taking medication too late in the day can disrupt sleep, causing next-day fog)
Wearing-off effects as medication leaves your system

Other medications:

Antihistamines (especially older, sedating types like diphenhydramine)
Some blood pressure medications (beta-blockers can affect cognition)
Certain antidepressants (particularly more sedating ones)
Sleep aids and anxiety medications (benzodiazepines, Z-drugs, atypical antipsychotics)
Pain medications (opioids, muscle relaxants)
Anticholinergic medications (overactive bladder treatments, some antiemetics)

Medication interactions:

Taking multiple medications that affect the brain can compound sedating effects
Some combinations interfere with how medications are metabolised

Important: Don't adjust or stop medications on your own. If you suspect your medication is contributing to brain fog, discuss this with your prescribing doctor. Sudden changes—especially to ADHD medications, antidepressants, antipsychotics or anxiety medications—can cause withdrawal effects or symptom rebound. Your doctor can help you safely trial dose adjustments, timing changes, or medication switches under proper supervision.

5. Other Medical Conditions

Brain fog can be the presenting symptom of various medical conditions that have nothing to do with ADHD:

Thyroid and metabolic dysfunction

Hypothyroidism (underactive thyroid) is particularly common and causes cognitive slowing, fatigue, and difficulty concentrating
Blood sugar dysregulation (diabetes, prediabetes, reactive hypoglycaemia)

Nutritional deficiencies

Iron deficiency/anaemia (especially in people who menstruate, vegetarians/vegans)
Vitamin B12 deficiency (can cause memory problems and mental fog)
Vitamin D deficiency (linked to cognitive difficulties and mood problems)
Magnesium deficiency

Autoimmune and inflammatory conditions

Coeliac disease
Lupus
Hashimoto's thyroiditis
Rheumatoid arthritis
Multiple sclerosis

Sleep Disturbances

Sleep apnoea (separate from insomnia—involves breathing disruptions during sleep)

Adults with ADHD aren't at higher risk for these conditions necessarily, but they're human—these conditions happen to people with ADHD just like everyone else.

What About "Sluggish Cognitive Tempo"?

Evidence strength: Emerging but increasingly delineated

There's one more piece to this puzzle that's particularly relevant to understanding brain fog in ADHD: Sluggish Cognitive Tempo (SCT), recently renamed Cognitive Disengagement Syndrome (CDS) by researchers.

What is SCT/CDS?

SCT describes a distinct pattern of symptoms that often co-occurs with ADHD but appears to be a separate condition:

Mental fogginess and feeling "spacey": a persistent sense of being in a haze
Daydreaming and mind-wandering: appearing "in one's own world," even when trying to pay attention
Lethargy and low initiative: difficulty getting started, appearing unmotivated or sluggish
Slowed behaviour and thinking: processing information and responding more slowly than peers
Hypoactive presentation: physically still or underactive, rather than hyperactive

How SCT differs from ADHD inattention

This distinction is important: ADHD inattention typically involves being distracted by external stimuli or internal thoughts that pull attention away. You're thinking about many things, just not the right thing.

SCT, by contrast, involves mental underarousal and disengagement. You're not thinking about multiple things—your mind feels slow, blank, or drifting. People with SCT often describe feeling like they're "not fully present" or like their brain is "running in slow motion."

What the research shows:

Prevalence: SCT commonly overlaps with ADHD, reported in around 30-50% of clinical samples (though estimates vary by assessment method)
It's considered a separate condition from ADHD, though they frequently co-occur
Distinct cognitive profile: People with both ADHD and SCT process information more slowly across multiple tasks and have greater executive function challenges than those with ADHD alone
Different correlates: SCT correlates more strongly with internalising symptoms (depression, anxiety, social withdrawal) than with traditional ADHD features like hyperactivity or impulsivity
Not captured by ADHD criteria: Standard ADHD symptom scales often miss SCT features, which is why it's gone underrecognised

Why this matters: If you have SCT alongside ADHD, you might experience chronic mental fogginess that's separate from both your ADHD and from episodic brain fog from other causes. This is still an emerging area of research, but it validates that some people with ADHD do have an inherent tendency toward cognitive slowing and mental cloudiness.

Treatment note: Evidence for treating SCT/CDS is emerging. Some trials have examined ADHD medications in people with elevated SCT symptoms, but optimal treatment approaches remain an active research area. Traditional ADHD stimulants don't consistently help SCT symptoms as much as they help core ADHD symptoms.

So What's Causing YOUR Brain Fog?

If you have ADHD and you're experiencing brain fog, here's how to actually figure out what's going on:

Step 1: Describe Your Experience More Specifically

"Brain fog" is a starting point, but get more detailed:

When does it happen?

All the time, or episodically?
Worse at certain times of day?
Related to your menstrual cycle (if applicable)?
Better or worse on medication?

What exactly does it feel like?

Slowed thinking?
Can't find words?
Memory blanks?
Mind going completely blank?
Mental exhaustion?
Feeling "disconnected" or "spacey"?

Is this new or worsening?

Have you always felt this way (possibly SCT)?
Did it start at a specific time (menopause, after illness, new medication)?
Is it getting progressively worse?

Step 2: Rule Out the Most Common Culprits

Work with your doctor to investigate:

Sleep Assessment:

Do you snore, gasp, or wake frequently? (Consider sleep study for apnea)
Do you have trouble falling asleep or delayed sleep patterns? (Consider circadian rhythm evaluation)
How many hours of quality sleep are you actually getting?
Do you wake feeling refreshed or still exhausted?

Mood Evaluation:

Are you experiencing symptoms of depression (low mood, reduced interest, hopelessness)?
Do you have significant anxiety (constant worry, feeling keyed up, panic)?
How's your stress level?
Have you gone through significant life changes or transitions?
- Bereavement or loss
- Relationship breakdown, separation, or divorce
- Job loss, redundancy, or major career change
- Moving house or relocating
- Becoming a parent or major shifts in parenting demands
- Taking on caregiving responsibilities for family members
- Chronic illness diagnosis (yours or someone close to you)
- Major financial stress or instability
- Trauma or significant adverse events

Medical Screening:

Thyroid function (TSH, Free T4)
Iron studies (ferritin, especially if you menstruate)
Vitamin B12 and D levels
Blood sugar/HbA1c
Basic metabolic panel

Note: This isn't a checklist you need to self-order, your GP can tailor investigations based on your symptoms, history, diet, and risk factors.

Medication Review:

List all medications and supplements
Are any known to cause cognitive side effects?
Is your ADHD medication optimally dosed?

Hormonal Assessment (if applicable):

Women in perimenopause: FSH, estradiol levels
Correlation with menstrual cycle?

Step 3: Consider Whether This Might Be SCT

If your "fog" is chronic (not episodic) and characterised by mental fogginess, daydreaminess, and low initiative, even when you've addressed:

Sleep problems (treated sleep apnoea, improved sleep hygiene, consistent schedule)
Mood disorders (depression and anxiety adequately treated)
Medical issues (thyroid, nutritional deficiencies corrected)
Medication effects (ADHD medication optimised, sedating medications reviewed)
Hormonal factors (if applicable, assessed and managed)

Then discuss SCT/CDS assessment with a knowledgeable clinician. The persistence of fogginess despite addressing these common causes may indicate SCT as a separate factor.

Step 4: Don't Assume It's "Just ADHD"

Here's the most important message: If you have ADHD and brain fog, investigate what's causing the fog rather than just accepting it as part of ADHD.

The research is clear: brain fog in ADHD is usually driven by comorbid conditions—especially sleep problems, mood disorders, and (in women) hormonal factors.

Treating these underlying issues can dramatically improve cognitive clarity, often more effectively than adjusting ADHD medication alone.

What Actually Helps (Evidence-Based Approaches)

Once you know what's causing your brain fog, treatment becomes clearer:

If It's Sleep:

Highest-yield interventions:

Sleep study and treatment for sleep disorders (especially apnea—CPAP machines can be transformative)
Sleep hygiene (consistent schedule, dark room, cool temperature, no screens 1 hour before bed)
Light therapy for delayed sleep phase (bright light exposure in the morning)
Sometimes melatonin (carefully timed, discuss with doctor)
Treatment for insomnia (CBT for insomnia is highly effective)

Why this matters so much: Sleep interventions can "reverse a source of cognitive impairment" in ADHD. This is often the single biggest win.

If It's Mood/Anxiety:

Evidence-based therapy (CBT, DBT)
Antidepressant or anti-anxiety medication if appropriate
Stress management techniques
Sometimes adjusting ADHD medication (some can worsen anxiety)

Research shows these are the strongest correlates of subjective cognitive complaints in ADHD—addressing them directly often provides more cognitive relief than expected.

If It's Hormonal:

Consult with a provider knowledgeable about ADHD and hormones
Consider hormone replacement therapy in menopause (consult specialist—not right for everyone)
May need ADHD medication dose adjustments at different cycle phases or life stages
Some women benefit from continuous birth control to reduce hormonal fluctuation

If It's Medical:

Many medical causes of brain fog are straightforward to treat once identified:

Thyroid disorders: medication for hypothyroidism typically improves cognitive symptoms within weeks to months
Nutritional deficiencies: iron, B12, or vitamin D supplementation when deficient (check levels first)
Blood sugar management: treating diabetes or prediabetes, dietary changes for reactive hypoglycaemia
Treating other conditions: coeliac disease, autoimmune conditions, MS

If Your ADHD Itself Is Under-treated:

Sometimes optimising ADHD treatment directly improves cognitive function:

Medication optimisation: right medication type, appropriate dose, optimal timing
CBT for ADHD: builds practical organisational skills and cognitive strategies for managing executive function challenges
Environmental modifications: external memory systems (lists, calendars, reminders), visual cues, body-doubling, task simplification
Regular physical exercise: aerobic exercise improves attention, mood, and executive function

What Probably Won't Help Much:

Let's be honest about the evidence:

Cognitive training/brain games:

Research shows limited transfer to daily functioning
Effect sizes shrink with better controls and blinding in studies
Doesn't meaningfully reduce ADHD symptoms or generalise to real-world tasks
Save your time and money

Over-the-counter supplements (most):

Very limited evidence for most supplements marketed for brain fog
Generally not a substitute for addressing underlying causes

The Bottom Line: Investigate, Don't Assume

Brain fog is real. Your experience is valid. And there's probably something specific causing it that can be identified and addressed.

The key shift: Stop thinking "I have ADHD brain fog, what treats that?"

Start thinking: "I have ADHD. I also have brain fog. These might be related, but the fog is likely coming from something specific—sleep, mood, hormones, medical issues —that I can investigate and address."

Because here's what the research shows:

Brain fog isn't an ADHD symptom
It's not specific to ADHD
In people with ADHD, it usually signals comorbid conditions
Treating those conditions often provides dramatic improvement

Your ADHD is real. Your brain fog is real. But they're probably not the same thing.

Figure out what's causing your fog, and you'll finally be able to clear it.

When to Seek Urgent Medical Attention

While brain fog is usually not an emergency, seek immediate medical evaluation if you experience:

Sudden onset of severe confusion or disorientation
Rapidly worsening cognitive symptoms over days or weeks
Confusion accompanied by fever, severe headache, or stiff neck
New neurological symptoms (weakness, numbness, vision changes, difficulty speaking, loss of coordination)
Severe sleepiness where you can't stay awake during the day (possible sleep apnea or other serious condition)
Fainting, dizziness, or near-fainting episodes
Cognitive changes after head injury
Confusion with chest pain or difficulty breathing

These symptoms may indicate conditions requiring immediate assessment (infection, stroke, severe metabolic disturbance, or other acute medical issues) rather than the gradual brain fog discussed in this article.

When to Seek Professional Help

See a healthcare provider if:

Brain fog is new, severe, or rapidly worsening
It's significantly impacting your work, relationships, or daily functioning
You suspect sleep disorders (especially if you snore, gasp at night, or have excessive daytime sleepiness)
You're experiencing mood changes, hopelessness, or anxiety alongside the fog
Simple lifestyle changes haven't helped
You're considering changing medications

A comprehensive evaluation—including ADHD assessment, comorbidity screening, sleep evaluation, and basic medical workup—is the most effective way to identify what's actually going on and get targeted treatment.

You don't have to live with brain fog. Understanding what it really is, and what's causing yours specifically, is the first step toward thinking clearly again.

At Kantoko

We specialise in ADHD assessment and medical management for adults. Whilst we focus on assessing and treating ADHD rather than brain fog specifically, understanding whether your ADHD is optimally managed is an important first step in working out what's contributing to your cognitive difficulties.

If your assessment suggests other factors at play, sleep disorders, mood issues, or medical conditions, we can help guide you toward appropriate investigations.

If you're ready to explore whether your ADHD needs better management, Get started with us today.

Frequently Asked Questions

What is ADHD brain fog like?

Many people with ADHD describe experiencing brain fog as a sense of mental cloudiness or heaviness, where thoughts feel slower, less clear, or harder to access. It can show up as losing your train of thought, struggling to organise ideas, zoning out in conversations, or finding it difficult to shift between tasks.

However, brain fog isn't actually a core symptom of ADHD itself—it's usually a signal that something else is going on, such as sleep problems, mood issues, hormonal changes, or other medical factors. Understanding what's causing your brain fog is the key to addressing it effectively.

How do you get rid of brain fog when you have ADHD?

The most effective approach is identifying what's actually causing your brain fog, rather than treating it as simply an ADHD symptom. Many people find improvement by addressing underlying issues: treating sleep disorders (especially sleep apnoea), managing depression or anxiety, correcting nutritional deficiencies, optimising medications, or addressing hormonal factors.

Some people also benefit from practical supports like external reminders, consistent sleep routines, and executive function tools such as timers or visual planning systems. ADHD medication can help if your ADHD itself is undertreated, but addressing comorbid conditions (especially sleep and mood) often provides more dramatic cognitive improvement. A clinician can help you investigate what's driving your brain fog and guide you towards the most effective interventions for your specific situation.

What is the burnout cycle of ADHD?

The ADHD burnout cycle is a pattern where you push through tasks using bursts of effort, become mentally and emotionally exhausted, experience brain fog and reduced performance, feel anxious about falling behind, and then push even harder to compensate—restarting the loop. This cycle is common and often linked to masking (hiding ADHD traits), perfectionism, chronic stress, and inadequate rest or recovery time. Breaking the cycle typically requires addressing the underlying causes of exhaustion (sleep, emotional regulation, workload management) rather than simply trying to push through harder.

What is the 24-hour rule for ADHD?

The 24-hour rule for ADHD is a practical strategy that encourages you to pause for a day before responding to something emotionally charged or making a significant decision.

This buffer helps regulate emotional responses, reduces impulsive reactions that you might later regret, and gives your brain time to process and reset. It's particularly helpful for people with ADHD who experience emotional dysregulation or make impulsive decisions during stressful moments. By building in this pause, you create space for clearer thinking and more considered responses.

This article is for informational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for treatment.