For years, it was believed that there was a hard line between Autism Spectrum Disorders (ASD) and Attention Deficit Hyperactivity Disorder (ADHD) within the field of psychology; if you had one you could not be diagnosed with the other. Recent evidence, however, has revealed the opposite. According to a 2017 study found in Eur Child Adolesc Psychiatry, over half of people with ADHD have some comorbidity with one or more psychiatric issues . Solid numbers remain elusive, but experts can extrapolate that the two are not as segregated as they were once believed.
So what are these disorders, and how are they both different to each other? How are they similar to each other?
ADHD is a neurodevelopmental disorder commonly found in children that can continue into adulthood. This disorder affects many areas of the brain including (but not limited to) executive functions in the brain, impulse control, and attention span. ADHD is typically diagnosed when a child is in kindergarten or preschool. However, many adults will get a diagnosis later in life if ADHD was not caught as a child. While they are able to understand social cues and other neurotypical behavior, people with ADHD have a tendency to feel restless in class, work, or any time they are trying to stand still. Due to this, they will frequently find it very hard to focus on tasks for a long period of time.
ASD, as the name implies, is a spectrum of neurodevelopmental symptoms that can cause challenges with communication, as well as display restrictive and repetitive behaviors. Typically, ASD is noticeable in children before they are two years of age, though many individuals can be left undiagnosed due to how symptoms manifest differently in individuals, based on a variety of factors including sex, family environment, and more. People with ASD tend to have problems with social interactions, be sensitive to certain textures and/or noises, and tend to find it challenging to manage emotions and facial expressions. They may also be sensitive to sudden changes to their regimented routines.
The disorders overlap most frequently when it comes to the topic of maintaining focus. Sometimes, when a person with ADHD is able to fixate on a specific task, they can do so for hours at a time, and not focus on anything else. People on the autism spectrum do something similar, often "overfocusing" on a task so much that it becomes very hard to move towards the next task. Unlike people with ADHD, though, autistic individuals often overfocus as part of a strict routine. As a result, if their routine is disrupted, everything else falls apart.
While there may be some overlap between the two disorders, treating both can be difficult, since they have a tendency to conflict with one another in different ways. For both ASD and ADHD, behavioral therapies such as cognitive behavioral therapy (CBT) have been shown to have benefits for both disorders across the spectrum. However, medications will most likely benefit ADHD symptoms, with a strong amount of evidence to support this theory. Dr William Dodson, a psychiatrist specializing in childhood ADHD and autism, says that “few people with both ADHD and ASD succeed without medication to remove the additional obstacle of ADHD from their path.”  Therapy tends to benefit ASD symptoms more often than ADHD symptoms. Diagnosing and treating someone with both disorders also tends to be a long, ongoing process, as opposed to a single, fixed diagnosis. As people age, their behaviors can change, and other symptoms that weren't present originally can manifest suddenly. Thus, individuals with ADHD, ASD, or both find it very important to continue to see professionals in order to learn how to best manage their symptoms.
Having either one of these conditions is a struggle to cope with, but having both at the same time can make getting proper, accurate treatment difficult. However, now that psychologists know more, they can start correcting the diagnostic procedures for both mental conditions and make sure that everyone has access to help when they really need it.
: Reale L, Bartoli B, Cartabia M, Zanetti M, Costantino MA, Canevini MP, Termine C, Bonati M; Lombardy ADHD Group. Comorbidity prevalence and treatment outcome in children and adolescents with ADHD. Eur Child Adolesc Psychiatry. 2017 Dec;26(12):1443-1457. doi: 10.1007/s00787-017-1005-z. Epub 2017 May 19. PMID: 28527021.
: Marner, Kay. “Is It ADHD or Autism? Or Both?” ADDitude, ADDitude, 8 Feb. 2021, www.additudemag.com/is-it-adhd-or-asd/.