What Should and Shouldn’t Be Considered a “Serious” Mental Illness?

Out of all the 300 unique mental illnesses identifiable in the Fifth Edition, Diagnostic and Statistical Manual of Mental Disorders (DSM-5), there is a small subset of serious mental illnesses (SMIs). Although the border between what is considered a serious mental illness and what is not is still hazy, extreme cases can clearly be dangerous both to a person and those around them.

To identify what exactly is a “serious” mental illness, here are the summaries and statistics of three different efforts by different organizations/institutions to help identify SMIs, their severity, the relevant statistics, and other things you need to know about them:

The Center for Mental Health Services (CMHS)

According to the Center for Mental Health Services, an SMI as a mental illness diagnosable via the DSM-5. For it to be considered an SMI, the illness must cause a functional impairment/s that may interfere in major life activities. Some examples include schizophrenia, bipolar disorders, and major depression.

In the DSM-5, “functional impairment” is loosely defined as limitations experienced in the social or occupational aspects in life caused by an illness. The CMHS gave their own definition of what a “functional impairment” is, and from there found disturbing statistics.

According to their findings, 90% of people who meet the criteria for a serious mental illness either have a severe disorder (like schizophrenia or bipolar disorder), a disorder and work impairment, or a disorder and suicidal tendencies.

By all accounts, serious mental illnesses include “schizophrenia-spectrum disorders,” “severe bipolar disorder,” and “severe major depression” as specifically and narrowly defined in DSM. People with those disorders comprise the bulk of those with serious mental illness. However, when other mental illnesses cause significant functional impairment and substantially limit major life activities they also count as a serious mental illness.

National Institute of Mental Health (NIMH)

According to the National Institute of Mental Health, serious mental illnesses are relatively rare as it affects about only 5% of people aged over 18 years old.

The NIMH considers the following as serious mental illnesses: schizophrenia, “severe major depression”, “severe bipolar disorder”, and a few other disorders that are classified as “severe”.

For reference, here are some statistics of the NIMH:

  • All cases of schizophrenia are considered severe under the NIMH and affect 1.1% of the population.
  • Bipolar disorders that are categorized as “severe” cases affect 2.2% of the population.
  • Major depression categorized as “severe” cases affect 2.0% of the population

In summary, about 5.3% of the total adult population is diagnosed with a severe/serious mental illness, without taking overlapping diagnosis into account.

National Advisory Mental Health Council (NAMH)

The National Advisory Mental Health Council has made efforts to define what a serious mental illness as well as determine how much it affects the population.

The study conducted took place back in 1993 when the Senate Committee on Appropriations (SCA) asked the NAMH to report on how much it would cost to provide insurance coverage for those people diagnosed with “severe mental illnesses” commensurate with the coverage of any other illnesses.

According to their study, “severe mental illness” is defined through a specific diagnosis, the disabilities that come from the illness, and how long the illness lasts. These disorders include psychosis, schizophrenia, schizoaffective disorder, manic depressive disorder, autism.

Mental illnesses are also deemed serious if they are deemed as a “severe” case. These include disorders like major depression, bipolar disorders, panic disorder, and obsessive-compulsive disorder.

Similar to the studies conducted by the Center for Mental Health Services (CMHS), they concluded that 3% of people aged over 18 years old are clinically diagnosed with a mental illness, around the same percentage found with the CMHS and NIMH.

Most of the money spent in the US on mental healthcare usually focus solely on serious mental illnesses more than any other kind of mental health diagnosis. This is a big problem in the US mental healthcare system as it does not take into consideration how “minor” mental illnesses could develop into more serious kinds.

Prevention is always better than cure, and the case for mental health degradation prevention should be the same. If we give priority to serious illnesses, we can treat them faster and more efficiently. Likewise, investing in keeping the public’s mental health in a good condition can improve everyone’s outlook in life.


Mental illnesses are considered serious when it can incapacitate a person’s capability to socialize, work, communicate, and act. Serious mental illnesses (SMIs) have to be diagnosed by a professional mental healthcare worker and are specified under the Fifth Edition, Diagnostic and Statistical Manual of Mental Disorders (DSM-5). In the context of seeking therapy, it’s important to note that the types of therapists and treatment methods available may also differ between countries, with someone in Dallas seeking therapy and looking for a therapist Dallas potentially having access to different options than someone in a different part of the world.

When it comes to your mental health, just like any other illness, prevention is always better than cure. To learn more about SMIs, you can visit [blog link] to learn more for yourself or for a loved one.