One of the largest public mental health service agencies in my local area asks the question, "What is mental illness?" on their website.  In answer they state, "Mental illness is a biologically based disease, much like diabetes or cancer," and,"most researchers agree it involves a chemical imbalance in certain parts of the brain."  Frequently when we encounter a declarative statement made by a perceived authority, we accept it and integrate that information into our way of thinking about things. But is this statement accurate?  What is its basis, and what is the evidence behind the statement?  We are told that "most researchers" agree - is that true?  How can we know?

Let's look more closely at the public talking points about "mental illness" as championed by the two most powerful institutions in mental health today:  The American Psychiatric Association and the Pharmaceutical industry. And then let's contrast these statements with statements that can actually be supported by a coherent body of empirical research.
Claim: Mental Disorders are brain diseases cause by neurotransmitter dysregulation, genetic anomalies, and defects in brain structure and function.
Evidence: scientists have not identified a biological cause of, or even a reliable biomarker for, any mental disorder.
Claim: Psychotropic medications work by correcting the neurotransmitter imbalances that cause mental illness.
Evidence: there is no credible evidence that mental disorders are caused by chemical imbalances, or that medicines work by correcting such imbalances.
Claim:  Advances in neuroscience have ushered in an era of safer and more effective phamracological treatments.
Evidence: modern psychiatric drugs are generally no more safe or effective than those discovered by accident a half-century ago.
Claim: biological psychiatry has made great progress in reducing the societal burden of mental disorder.
Evidence: mental disorders have become more chronic and severe, and the number of people disabled by their symptoms has steadily risen in recent decades.
Claim:  educating the public that mental disorders are biologically-based medical diseases reduces stigma.
Evidence: despite the public's increasing endorsement of biological causes and treatments, stigma has not improved and shows signs of worsening.
Claim:  increased investment in neuroscience research will lead to diagnostic biological tests and curative pharmacological treatments.
Evidence: the pharmaceutical industry has dramatically scaled back efforts to develop new psychiatric drugs due to the lack of promising molecular targets for mental disorders and the frequent failure of new compounds to demonstrate superiority to placebo.
The above summary comes from an article by Brett J. Deacon published in the Journal of Clinical Psychology in 2013.   The article is titled, The Biomedical Model of Mental Disorder: A Critical Analysis of its Validity, Utility, and Effects on Psychotherapy Research.  At my personal blog, Madness and Civilization, you will find a heading called "Critical Research" that includes a reference list with links to thousands of pages of peer-reviewed research and articles spanning over five decades.

There is in fact no conclusive evidence to support the claim that mental illness is a biological disease like diabetes or cancer.  As of 2014, there is not one single medical test for any of the over two hundred diagnoses listed in the bible of Psychiatry and mental Health, the Diagnostic and Statistical Manual of Mental Disorders (DSM.)  This, despite over a half-century and billions of dollars spent in the pursuit of finding a root biological cause to cognitive and emotional distress.  There is no objective criteria for reliably "diagnosing" any mental disorder.  Every diagnostic criteria specified in the DSM is a subjective assessment made by an individual clinician without any reliable objective measurement.  No one can tell you that you "have" Bipolar Disorder or Schizophrenia, only that your own subjective expression of your experiences meets certain categorical definitions of the label in the opinion of some clinician and some time.

Where does this leave us?  It leaves us with the need to question whether the phrase "mental illness" makes any sense at all.  Stephen Morgan writes that, "mental illness itself - the idea that a mind is ill - is actually a categorical error, like saying the sky is ill or the color green is healthy."  And yet people can and do experience very extreme thoughts and feelings all the time.  These intense experiences can be immensely distressing, and even dangerous - either to the person or to other people.  Certainly this sort of distress is a very real, very painful human experience.  As so we often casually refer to these experiences as "mental illness."  If and when we do this, I believe we have an obligation to acknowledge that we have no empirical evidence that any sort of biologically based mental illness exists.  The term mental illness is, at best, a metaphor.

One way to define the kinds of experiences that get wrapped up in the metaphor of mental illness is like this:  unusual or extreme thinking and feeling states.   That's all we are really talking about - states of thinking and feeling that are judged to be unusual by societal standards, or considered to have extreme negative impact on either the individual experiencing these states or on those around the person.  Unusual thinking and feeling states can vary from minimally impacting to very dangerous.  Nothing about acknowledging the lack of empirical evidence for a biological definition of "mental illness" takes away from the serious problems extreme thinking and feeling states can sometimes create.

But the mental health system's insistence that mental illness is a literal brain disease has had disastrous implications for how support is offered.  The overemphasis on psychotropic medications as the first and primary action coupled with the evidence-absent insistence that people will never recover and should take psychotropic drugs for the rest of their life has led to an explosion of disability, increasing cognitive and emotional distress, and severe adverse health effects.  The insistence that mental illness is a disease has led to increasingly coercive "treatment" of the "mentally ill" including forced drugging, involuntary incarceration, the striping of civil rights, and more.  None of this has lead to a decrease in the number of people enrolled in social security disability due to a "mental illness."  In fact, the number of people on disability increases each and every year.  Overall, the United States has some of the worst mental health outcomes in the entire world.

We are doing something terribly, tragically wrong.

An alternative to the literalization of "mental illness" is an approach that expresses and appropriate humility about the limits of what we know about the brain, the mind, and the human experience.  Instead of looking to diagnosis a "mental illness," therapists can look to understand an individuals thinking and feeling states that may cause them distress or cause them to be at risk among others. We have every reason to see these states as simply part of a spectrum of human response to our experiences.  We can consider the possibility that any "well" person, given the right set of circumstances and experiences, can and will experience unusual or extreme thinking and feeling states. Likewise, because a person experiencing such states is not "sick" in any literal sense, we can also maintain that anyone can recover from thinking and feeling states that are distressing to them.  People can and people do all the time.

We can also make an educated guess (based largely on common sense) that factors which contribute to unusual or extreme thinking and feeling states are a combination of biological processes occurring through the whole body (not just the brain,) psychological factors of a persons internal processing, coping and meaning-making, and social factors of history, culture and context.  This extremely reasonable assumption has major implications for anyone interested in helping others navigate the dynamic and complex waters of thinking and feeling.

For more discussion of the subject of the mental illness myth and metaphor, please see my article: An Open Letter to Persons Self-Identifying as Mentally Ill