ADHD and Autism: Understanding the Differences, the Overlap, and the Diagnostic Challenges

Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD) are both neurodevelopmental conditions that affect behaviour, communication, and regulation. Although distinct in their clinical presentation, they share a number of overlapping traits, particularly when it comes to emotional regulation and social communication. As a result, distinguishing between the two—or recognising when both are present—can be complex.

Distinguishing Traits
ADHD is primarily characterised by persistent patterns of inattention, impulsivity, and—in some cases—hyperactivity. Children and adults with ADHD may appear forgetful, disorganised, easily distracted, or constantly on the go. For many, there is a strong internal need for stimulation and novelty. Inattentive presentations may be more subtle, marked by daydreaming, mental drift, and difficulties with sustained focus.

Autism, on the other hand, is defined by difficulties with social communication, restricted or repetitive behaviours, and heightened sensory sensitivities. Individuals with autism often seek routine and predictability, and may struggle to interpret social cues or adapt to changes in their environment. While not every autistic individual exhibits rigid behaviours or sensory issues, these are hallmark features of the condition.

Where They Overlap
Despite their differences, ADHD and autism can share several challenges, including:

• Difficulties with impulse control

• Trouble regulating emotions

• Challenges interpreting social cues

These shared traits can lead to significant diagnostic confusion. For instance, a child who struggles to maintain eye contact, interrupts frequently, or becomes overwhelmed in busy environments could meet criteria for either ADHD, autism, or both. In fact, research indicates that co-occurrence is common—many individuals diagnosed with one condition also meet diagnostic criteria for the other.

The Challenge of Diagnosis
One of the major clinical challenges is that traditional diagnostic tools and criteria were developed to assess each condition in isolation. In practice, however, the presentation is often more nuanced. A child with autism might appear inattentive because they are overwhelmed by sensory input. Conversely, a child with ADHD might exhibit repetitive behaviours simply as a means of self-stimulation or emotional regulation.

Gender can further complicate the picture. Girls and women are often underdiagnosed in both conditions, partly due to better masking and more internalised symptoms. Inattentive ADHD, in particular, may be misinterpreted as anxiety or low mood. Similarly, autistic individuals who speak fluently and mimic social norms may have their difficulties overlooked.

Why an Accurate Diagnosis Matters
Understanding whether someone is experiencing ADHD, autism, or both is critical to tailoring appropriate support. Interventions for ADHD often focus on managing attention, impulsivity, and executive functioning, while autism support may prioritise sensory regulation, structured routines, and social communication strategies. Without clarity, individuals may receive ineffective interventions or experience worsening self-esteem and mental health.

At the London Psychologist Clinic, our assessments are designed to go beyond labels. We work holistically, recognising the individuality of each client and the many ways neurodivergence can manifest across the lifespan. Our approach integrates cognitive testing, clinical interviews, and behavioural analysis to support clarity and confidence in diagnosis.

Autism and ADHD are not simply checklists of symptoms—they are deeply personal ways of experiencing and processing the world. A nuanced understanding is key to compassionate care. With the right insight and support, individuals with either—or both—conditions can thrive.