Mental Illness vs. Mental Disorder

Katelyn Hagerty

Reviewed by Katelyn Hagerty, FNP

Written by Geoffrey Whittaker

Updated 01/10/2023

If you’ve been learning about mental health for some time now, things might be starting to make more sense. But you may still have a few seemingly easy-to-answer questions, like the differences between mental illness versus mental disorder.

Anxiety, depression, bipolar, trauma — many terms help define what makes us tick and behave the way we do. The symptoms, signs and potential causes of these conditions all paint a picture of what goes on inside our heads when we’re disordered or struggling.

But how disorders differentiate from illnesses can be somewhat harder to explain. 

Truth be told, many experts use mental illness to describe disordered thinking all the time. It’s a more common phrase than mental disorder — and one the average person is often comfortable with.

But you’re above average — we can tell just from where you’ve come to get answers to this question. Smart people like yourself deserve a little more depth to their answers than what the first page of a Google result offers.

So, what’s the difference between a mental disorder and a mental illness? Here’s what you need to know.

There are lots of confusing things to unpack in this discussion, so we’ll inject some order into the process. Let’s start with disorders because, well…they come first, alphabetically. 

A mental disorder is a mental health condition in which your thoughts, feelings, moods or behaviors are adversely affected by something. This may cause you distress or difficulty performing normal daily activities or tasks.

When a medical professional uses the term disorder, they’re indicating something is wrong, though the reason may not be entirely clear yet.

Ready for things to get immeasurably complicated? Here goes. The National Library defines mental disorder as a term interchangeable with mental illness.

Arguably, we could stop there. They mean the same thing — so case closed, right? But it’s not actually that simple.

According to a separate resource from the National Library of Medicine (NLM), a mental illness is a health condition that changes how a person thinks, behaves or feels (or sometimes all of the above).

These changes result in distress for the person in question. They may find it difficult to function the way they did previously in many situations.

A person with a mental illness may:

  • Be less productive at work

  • Struggle to connect emotionally with friends, family or a partner

  • Become irrational, agitated or irritable in interactions with others

  • See the world through a different (and less accurate) lens

And according to the NLM, these illnesses vary in intensity from person to person. This means two people with the same so-called mental illness may have completely different experiences in terms of distress or reduced professional functioning, cognitive functioning or social functioning.

Common examples of mental illness include personality disorders, mood disorders and others like:

The National Institute of Mental Health (NIMH) points to a number of “disorders” under that banner, which leaves plenty of people wondering exactly what the difference is.

There’s an argument to be made that the only difference is ignorance — on behalf of the medical community.

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So what’s the difference, really? Maybe nothing. 

This question is difficult to answer because even the medical community, with all its wisdom (and the fact that its members are the ones writing the definitions), hasn’t come to a clear understanding of when and how disorder should be used.

A 2018 paper laid out the current state of affairs, citing the many changes that have occurred since the phrase was originally defined. Things have changed a lot over the decades since the Diagnostic and Statistical Manual of Mental Disorders (DSM) was first published. 

The DSM has been through several new editions and significant revisions over the years. One of the most prominent arguments is that homosexuality was considered a mental disorder until the mid-1970s.

To put a finer point on it: things are constantly changing. Many resources point to the move away from disorder to illness as a result of an increase in our knowledge about what causes mental illness.

Disorder can sometimes be used when there’s a problem, but we don’t know why it exists. For most of human history, we didn’t know why mental illness happened. And only in the last century has science begun to understand the complicated field of neuroscience and how genetics, environmental factors and biological factors affect our mental health.

Nowadays, added complications make disorder a less-than-ideal term. For instance, when we talk about the comorbidity of conditions like anxiety and depression, we technically can’t use the word disorder because (technically) comorbidity can only refer to the co-occurrence of illnesses and diseases, not disorders.

Now, maybe that argument is pedantic. You can just imagine the nerdiest med student making this point during a lecture — to the eye rolls of a dozen other lab coat-adorned nerds.

But to paraphrase a line of dialogue from one of the nerdiest TV shows ever aired, he would technically be correct — the best kind of correct. 

So where does this leave our discussion? Are the two terms interchangeable? Yes and no. 

In all cases, when you refer to a mental disorder as an illness, you’re using the right terminology. The NLM thinks so, anyway.

But the reason you see disorder continue to be employed is complicated.

The terms mental illness and mentally ill have been stigmatized over the decades. And the average person tends to be more empathetic to a disorder than an illness, which to the layperson, suggests something that can be caught or spread like a disease.

Nobody wants to think about a brain being diseased — not their own and not someone they have to interact with. It’s a social and cultural problem, but it’s also one that's arguably solved by the casual use of disorder when referring to mental illnesses.

If you ask us, there are still too many conflicting opinions to prevent you from using them interchangeably.

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The words you use to describe your mental health are determined by many factors. You may use mental illness and mental disorder interchangeably. Or you might also never use either of them again once you have a formal diagnosis.

And in case you were wondering, that’s your next step: finding out what’s actually happening inside your head. 

Disorder versus illness is really just semantics compared to the real, beneficial treatment options you could be pursuing at this time.

Mental health treatment, psychological treatment and various behavioral treatments all fall under the banner of effective treatments when conducted with professional support.

Effective treatment options can take a lot of forms. Medication and exercise can benefit your mental health greatly, and so can therapy.

You may have already talked to someone about your mental health concerns. But if your behaviors and thoughts are disrupting your life, it may be time to start those conversations in earnest, possibly with formal mental health treatment. 

You can find mental health professionals just about anywhere.

Colleges and universities often provide on-campus resources, and religious and other community organizations can direct you to professionals as well. Another great place to get help is simply with your existing general practitioner.

But if those resources aren’t available or ideal for your sense of comfort and safety, we have one other suggestion: talk to us. 

The Hers online therapy platform is a great place to talk conveniently and safely with a mental health professional without ever leaving your home. It’s available 24/7, anywhere you have an internet connection. Our mental health resources can also help you find the support you need.

Mental illness and mental health disorders have one more thing in common we didn’t mention: they’re treatable medical conditions. Reach out and start treatment today.

6 Sources

Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references.

  1. Stigma and discrimination. (n.d.). Retrieved December 14, 2021, from
  2. U.S. National Library of Medicine. (n.d.). Mental disorders. MedlinePlus. Retrieved December 6, 2022, from
  3. Cooper J. (2004). Disorders are different from diseases. World psychiatry : official journal of the World Psychiatric Association (WPA), 3(1), 24.
  4. Telles-Correia, D., Saraiva, S., & Gonçalves, J. (2018). Mental Disorder-The Need for an Accurate Definition. Frontiers in psychiatry, 9, 64.
  5. National Institutes of Health (US); Biological Sciences Curriculum Study. NIH Curriculum Supplement Series [Internet]. Bethesda (MD): National Institutes of Health (US); 2007. Information about Mental Illness and the Brain. Available from:
  6. U.S. Department of Health and Human Services. (n.d.). Mental illness. National Institute of Mental Health. Retrieved December 6, 2022, from

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.

Katelyn Hagerty, FNP

Kate Hagerty is a board-certified Family Nurse Practitioner with over a decade of healthcare experience. She has worked in critical care, community health, and as a retail health provider.

She received her undergraduate degree in nursing from the University of Delaware and her master's degree from Thomas Jefferson University. You can find Katelyn on Doximity for more information.

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