Diagnosing ADHD and Autism in Adulthood

Medically Reviewed by Dan Brennan, MD on July 12, 2022
5 min read

Autism (ASD) and ADHD are two common conditions among adults. More than 5 million adults – about 2.2% of the overall U.S. adult population – have ASD, according to the CDC. Another 4.4% have attention deficit activity disorder (ADHD).

But what you might not realize is that you can have both. In fact, research suggests that anywhere from 28% to 44% of all adults diagnosed with ASD (autism spectrum disorder, or autism) may also have ADHD.

Just a couple of decades ago, most doctors wouldn’t think to screen adult patients for either condition. This meant many patients were in psychiatric treatment for years before they were formally diagnosed. Today, many health care providers are more aware of these developmental disorders and how they can affect adults. As a result, more and more people receive this double diagnosis.

It may seem like a lot to process if you or a loved one are diagnosed with both ASD and ADHD. But when you know, it allows you to find treatments and coping strategies that work for both.

Both conditions are neurodevelopmental disorders. This means that they affect brain development. So it’s not surprising that they both can affect movement, language, memory, social skills, and the ability to focus. Most notably, both affect your brain’s executive functioning. This impacts:

  • The ability to make decisions
  • Impulse control
  • Time management
  • Focus
  • Organization
  • Social skills

There appear to be certain other factors that explain why both often happen at the same time. They include:

  • Genetic changes. There are certain variations in genes that may make someone more susceptible to both ASD and ADHD.
  • A family history of one or both diseases.
  • Similar changes in brain structure. Research suggests that both ASD and ADHD have a link to disruptions in the corpus callosum, a bunch of nerve fibers that link your left and right brain.
  • Being male. Both conditions are more common in boys.

At first glance, the two may seem a lot alike. A person with either condition may:

  • Find it hard to pay attention
  • Have trouble with reading social cues
  • Have meltdowns
  • Invade others’ personal space
  • Move constantly

But there are also other key differences. Symptoms of ASD in adults include:

  • Difficulty with eye contact
  • Being emotionless and unexpressive (flat affect)
  • Poor conversation skills: changing the subject, rambling, or giving one-word answers
  • Awkward language skills: using formal, stiff words and sentences
  • A strong memory for details like facts, names, or statistics
  • Taking things literally
  • Fidgety, repeated behaviors like hand rubbing or rocking back and forth
  • Sticking to a routine and getting upset with changes
  • Being easily distracted by certain sights or sounds

In comparison, ADHD can cause very different symptoms, including:

  • Making seemingly careless mistakes
  • Being unable to pay attention for long tasks
  • Finding it hard to follow instructions
  • Being unable to organize things or tasks
  • Losing things such as keys, wallets, and phones
  • Forgetfulness
  • Having difficulty sitting still
  • Having trouble waiting
  • Talking too much and interrupting others

It can be difficult because if someone has mild symptoms of either or both conditions, they may have already come up with ways to make up for them. Someone with both ADHD and ASD may be friendly to others, for example, but just come across as a little “off.” It may be harder to pick up on concentration difficulties if a person is involved in an activity that really interests them. People with both conditions may also appear less distracted than someone with “traditional” ADHD, because they may tend to become preoccupied with a task more easily, or resist stopping.

It’s also challenging to diagnose people who also have intellectual disabilities, since the symptoms of ASD and ADHD may overshadow them. Some research suggests that 70% of people with an intellectual disability and ADHD also have ASD. But this may not always be the case. If a person has severe intellectual impairment, for example, and doesn’t speak (nonverbal), then they may get upset when they can’t communicate something. This looks like hyperactivity, but it really isn’t.

Since both are very complex conditions and can mimic each other, it’s important to have a very thorough evaluation. But many doctors now recommend that if you have a diagnosis for one of these conditions, you get screened for the other as well. Some adults with symptoms of mild ASD, for example, may never have gotten diagnosed in childhood because their symptoms of ADHD were so severe. But once they reached young adulthood, and their ADHD got better, their ASD became more clear.

Patient interview. Your doctor will review your personal, medical, and psychiatric history from childhood to the present. They may also ask you questions about how you manage your day-to-day life, such as:

  • Are there certain things like bright lighting, certain smells, or noises that make it harder for you to function?
  • Do you ever think about harming yourself or others?
  • Do you use illicit drugs or drink alcohol excessively?
  • Do you spend excessive amounts of time on the internet?
  • Do you ever notice that you pay no attention to things that bother others, like pain or changes in temperature?

Your doctor will also want to talk to others, such as your partner, a sibling, or parent, to get their impressions as well.

Behavior scales. Your doctor may have you or your significant other complete a rating scale that compares your behavior to people without ASD and/or ADHD. There are several different assessment scales they may use.

Medical exam. If you haven’t had a physical within the last 6 to 12 months, doctors usually recommend that you have one. This won’t diagnose ADHD, but it will rule out medical conditions such as thyroid or seizure disorders with symptoms that mimic ASD or ADHD.

Objective assessment. Your doctor may want to watch you in a specific setting, like at home or at work, to see how you function “in the real world.”

Generally, it’s a rougher road than for those with just an ADHD diagnosis. If you have both conditions, you have a greater chance of developing other mental health conditions such as depression and anxiety. Even if you’re not diagnosed with another condition, you may have extreme mood swings during the day that can be exhausting for both you and those around you.

Since an ASD/ADHD diagnosis is more challenging than either one alone, it’s important to find a treatment provider who specializes in both conditions. This way, you can help ensure that either you or your loved one gets the necessary care.