15 Common Symptoms of Adult ADHD: Could You Be Undiagnosed?

Have you ever felt like no matter how hard you try, you just can't stay focused, organised, or in control of your time? While many people struggle with these issues occasionally, for some, they may point to something more—Attention-Deficit/Hyperactivity Disorder (ADHD).

Though often associated with children, ADHD frequently continues into adulthood. In fact, it’s estimated that 3–4% of adults live with ADHD, yet many go undiagnosed for decades (Fayyad et al., 2007). The symptoms don’t just disappear with age—they evolve, sometimes becoming more difficult to detect.

Many adults mistakenly attribute their difficulties to personality flaws or a lack of willpower. But if you’ve struggled with attention, disorganisation, emotional regulation, or impulsivity most of your life, there may be another explanation.

In this guide, we’ll explore 15 common symptoms of ADHD in adults, why they occur, and the emotional impact of going undiagnosed. We’ll also look at how symptoms may present differently in men and women, and why a formal diagnosis can be a transformative step—even later in life.

15 Common Symptoms of Adult ADHD (and Why They Happen)

1. Difficulty Concentrating or Staying Focused

ADHD affects the brain's executive functions, particularly the prefrontal cortex, which helps manage attention. This can make it difficult to focus on tasks that aren’t inherently stimulating—even if they’re important. Adults often find their minds wandering in meetings, during conversations, or when reading. It’s not a matter of motivation—it’s a neurological difference.

2. Chronic Disorganisation

Do you constantly misplace your phone or struggle to keep your schedule on track? This isn’t laziness—it’s linked to deficits in working memory and planning. ADHD makes it hard to prioritise, structure tasks, and follow through on multi-step processes, even when you're trying your best.

3. Forgetfulness in Daily Life

Adults with ADHD often forget appointments, lose track of important dates, or fail to remember instructions. This is tied to issues with short-term memory and information retention, both of which are executive functions affected by ADHD.

4. Impulsivity

ADHD can reduce your brain’s ability to pause before acting. This may show up as interrupting conversations, impulsive spending, or difficulty waiting your turn. The reward system in ADHD brains is wired for immediate gratification, often bypassing rational decision-making.

5. Restlessness or Feeling "On Edge"

Adult hyperactivity isn’t always physical. Many report feeling internally restless, as though they’re mentally “revving” all the time. This can cause chronic stress, sleep issues, and a general sense of unease.

6. Difficulty Starting Tasks (Procrastination)

Task initiation problems are rooted in difficulty shifting mental gears. If something feels overwhelming, boring, or unclear, the ADHD brain may shut down. The result? Procrastination, guilt, and shame—despite the intention to act.

7. Poor Time Management

“Time blindness” is a hallmark of adult ADHD. You may underestimate how long something will take, overcommit, or run perpetually late. According to Barkley et al. (2008), adults with ADHD often struggle to estimate, monitor, and manage time effectively.

8. Mood Swings or Emotional Sensitivity

Adults with ADHD often experience intense emotions. The brain's emotional regulation system struggles to process frustration, rejection, or stress in a controlled way, which can lead to outbursts, tearfulness, or irritability.

9. Trouble Following Through on Commitments

You may start projects with enthusiasm, but lose momentum quickly. This isn’t due to a lack of care—it’s often a result of inconsistent attention and energy regulation, and the tendency to hyperfocus on new or more engaging distractions.

10. Low Tolerance for Stress

Everyday demands can feel like too much. With ADHD, the brain is constantly processing stimuli, making it harder to stay calm under pressure. This chronic overwhelm often leads to burnout.

11. Difficulty Listening or Retaining Information

Conversations can become challenging—not due to disinterest, but because your attention may drift without warning. This affects verbal working memory, making it hard to follow long explanations or instructions.

12. Trouble Relaxing or Unwinding

Many adults with ADHD describe their brains as “always on.” Whether it’s intrusive thoughts or endless to-do lists, the inability to switch off often leads to sleep problems, anxiety, and fatigue.

13. Frequent Job or Relationship Changes

Impulsivity, forgetfulness, and emotional intensity can strain relationships and affect job performance. You might change careers or partners frequently in search of “the right fit,” without realising ADHD symptoms are contributing to the dissatisfaction.

14. Sensation Seeking

ADHD brains crave stimulation due to lower baseline dopamine levels. This can lead to thrill-seeking, fast driving, risky behaviours, or constantly switching hobbies and interests.

15. Hyperfocus on Certain Tasks

While distraction is common, adults with ADHD can also become intensely focused on tasks that spark interest. This can be productive, but also disruptive if it causes you to neglect responsibilities or lose track of time.

Do ADHD Symptoms Differ Between Men and Women?

Yes, and understanding these differences is crucial for accurate diagnosis.

Men with ADHD:

• More likely to display externalising behaviours: hyperactivity, impulsivity, irritability.

• Diagnosed earlier due to disruptive behaviours, especially during school years.

• May engage in risk-taking behaviours or have frequent disciplinary issues.

Women with ADHD:

• More likely to experience internalising symptoms like inattention, anxiety, and low self-worth.

• Often misdiagnosed with anxiety or depression, delaying correct diagnosis.

• May “mask” symptoms by overcompensating—organising obsessively, overworking, or people-pleasing, which leads to burnout.

A study in The Lancet Psychiatry found that women are more likely to have inattentive-type ADHD and experience comorbid anxiety and depression (Ramsay & Rostain, 2020). Another study from the Journal of Clinical Psychiatry reported that women are typically diagnosed 5–10 years later than men (Quinn & Madhoo, 2014).

The Emotional Toll of Undiagnosed ADHD

Living for decades without knowing you have ADHD can deeply impact your self-esteem. You may have internalised the idea that you’re lazy, careless, or not trying hard enough—when in reality, your brain simply works differently.

Children with undiagnosed ADHD often receive frequent negative feedback:
“You’re not paying attention.”
“You’re too much.”
“Why can’t you just try harder?”

Over time, this consistent messaging can lead to toxic shame, self-doubt, and a persistent sense of being “not good enough.” This emotional weight often carries into adulthood, shaping career choices, relationship patterns, and risk of mental health conditions like:

• Anxiety disorders

• Depression

• Low self-esteem

• Substance misuse

A 2022 review in Frontiers in Psychology noted that adults with undiagnosed ADHD were significantly more likely to experience chronic anxiety, emotional dysregulation, and difficulties in interpersonal relationships (Sedgwick et al., 2022).

Why Seek an ADHD Diagnosis as an Adult?

You might ask: If I’ve made it this far, do I really need a diagnosis now?

The answer, for many, is yes—and here’s why:

Clarity and Self-Understanding

Receiving a diagnosis can provide enormous relief. It reframes years of struggle in a more compassionate light. Instead of self-blame, you gain insight into how your brain works—and why certain strategies haven’t helped in the past.

Access to Tailored Treatment

A diagnosis opens the door to evidence-based treatments such as:

• Medication (e.g., stimulants like methylphenidate or lisdexamfetamine)

• CBT for ADHD

• Coaching or occupational therapy

• Workplace accommodations

Improved Relationships and Communication

Understanding your patterns helps you communicate more effectively with others. Many people report better relationships with partners, friends, and colleagues after diagnosis.

Enhanced Self-Esteem

When you realise your struggles were due to neurology, not character, it can significantly boost your confidence and sense of self-worth.

When Should You Seek Help for Adult ADHD?

If multiple symptoms in this list resonate with you—and they’re affecting your work, relationships, or wellbeing—it’s worth exploring further.

At Matter of Health, we offer comprehensive adult ADHD assessments carried out by experienced psychiatrists. Our multi-disciplinary team ensures that your diagnosis is accurate, and your treatment plan is fully personalised.

We follow NICE guidelines, use validated tools, and provide follow-up support to help you manage your ADHD effectively and compassionately.

Take the First Step Toward Clarity and Support

You deserve to understand how your mind works—and to access support that empowers you to thrive. If you’ve spent years feeling out of step, distracted, or misunderstood, you’re not alone. ADHD is real. It’s manageable. And with the right diagnosis and support, things can get better.

Book your private adult ADHD assessment with Matter of Health today and take the first step toward a more confident, organised, and balanced future.