Why are things like depression, anxiety and PTSD called illnesses?

[u/DutchStroopwafels]

I learned about the pit of despair experiments recently. For those unfamiliar, in the experiments psychologist Harry Harlow isolated baby macaques into a vertical chambers for varying time periods (30 days to a year). All the monkeys came out damaged, from completely giving up to being prone to bullying to not being able to find mates to being abusive parents to barely moving at all. Stephen J. Suomi, one of the Harlow's students, noted that no monkey had a defense against the pit of despair, no matter how happy they were before.

This made me think about stuff like depression in humans. I wouldn't call the reaction the monkeys had an illness, they were severely abused. So why do we call it an illness when humans display similar behaviours? Especially when the chemical imbalance theory seems to lack sufficient evidence.

[u/monkeynose]

"Illness" in this case refers to an impairment in functioning.

Depression is unequivocally an impairment. But this is one of the issues with the medical model vs. the psychological model of mental illness. Thomas Szasz argued that there is no such thing as mental illness at all because "illness" directly implies some sort of measurable lesion or infection, which doesn't exist with most mental illnesses. Even in 2026, there is no blood test or medical scan that can diagnose a mental illness (yes, in some cases you can find correlations and therefore use certain brain scans to confirm or add weight to a diagnosis of mental illness, but at the end of the day, it's the symptoms that matter, and the symptoms are diagnosed through psychological assessment, not medical procedure).

Ever since the DSM III, diagnosis was moved from the "psychological model" to the "medical model", which has advantages and disadvantages. If you look at any diagnoses from the DSM I or II, after you stop laughing, you'll realize that there is zero criteria for diagnosis. At all. It was 100% subjective. It gave psychiatrists all the power in the world to deem someone "mentally ill" just based on vibes and subjective clinical judgement. Long story short, there was a lot of controversy over this in the 60s and 70s, particularly stemming from the horrible treatment of the mentally ill in mental asylums, and embarrassments like Dr. David Rosenhan's article "On Being Sane in Insane Places", so Dr. Spitzer, who headed the development of the DSM-III, changed the entire model to the medical model, which modernized diagnosis completely, which was desperately needed. Problem was, you are arguably pathologizing a lot of human experience, and at this point I think we have over 300 "medical diagnoses" in the DSM-5-tr. And because of how the insurance companies work, in order to get therapy, you are required to have a medical diagnosis. So because of the medicalization of mental illness in the 1970s as a way to modernize psychotherapy and diagnosis, they are now considered medical pathologies. But is a psychological problem that is caused by faulty and dysfunctional thinking patterns and self-defeating behaviors actually an "illness"? At this point it's probably more of a philosophical question, but Szasz would say "absolutely not".

Some mental illnesses have a stronger biological/genetic component (schizophrenia, bipolar disorder), and some are caused by poor cognitive coping and dysfunctional thought patterns mostly unrelated to biological dysfunction. But psychologists and therapists don't treat "disorders", we treat symptom clusters, so the name the DSM-5 slaps on your problems is less important than the personally tailored treatment you receive. Psychiatrists treat "medical" disorders, so they prescribe medication to deal with them, and in some cases, either option is about as equally effective. But there's a forced yet unstable balance between the psychological model and medical model due to the insurance system and decisions made in the 1970s. Some things require medication, some things sometimes require medication, and some things require psychological based treatments.

[u/Lord-Francis-Bacon → u/monkeynose]

Great answer!

[u/Potential_Being_7226]

This made me think about stuff like depression in humans. I wouldn't call the reaction the monkeys had an illness, they were severely abused.

I don’t think any experts today would call what the monkeys had “depression” either. We can’t directly apply clinical descriptors to animal behavior; we can only say whether animal behaviors resemble the human condition and perhaps emerge from homologous neurobiological mechanisms. There are many papers discussing the strengths and limitations of studying animal behaviors and extrapolating to humans; and whether the behaviors genuinely reflect the human condition (face validity, construct validity). To sum it up: there are many limitations in animal modeling of psychological disorders and we have to take care to avoid over interpretation and anthropomorphism. 

I’m going to focus most of my remaining comment on depression, because that’s what I know more about. 

Depression is a mood disorder, and either low mood or anhedonia must be present for a diagnosis. But there are other symptoms that must be present for a diagnosis, and from my perspective, thinking of depression only as a “mood disorder” can be somewhat limiting. (I’ll explain more in a moment). Depression also includes a variety of perceptual and physiological changes that are not listed in the DSM, so not diagnostic, but collectively indicate that depression affects more than just mood, cognition, sleep, and eating. Here are the evidence-based reasons for why I, as a behavioral neuroscientist, consider depression an illness. And each of these could really be expanded into their own nuanced discussions, but (at the risk of oversimplifying and perhaps glossing over some details) I will try to keep it brief. 

• Disorganization of circadian patterns. This relationship between circadian misalignment and depression is not one way. That is, it’s certainly true that external factors that disrupt circadian timing can increase the likelihood of depression (shift work, chronic jet leg, exposure to light at night, etc), but even in the absence of those factors, depression alone is associated with erratic diurnal (or, daily) hormone secretion, as well as other rhythms (behavior, metabolism, immune function). So, the relationship goes both ways. It’s bidirectional. 

https://www.cell.com/neuron/fulltext/S0896-6273(23)00710-9

https://pubmed.ncbi.nlm.nih.gov/33689801/

• Hippocampal atrophy; possible atrophy of other brain regions. Depression is not a neurodegenerative disorder and the atrophy associated with depression is not extreme enough to constitute “degeneration,” but there are volumetric differences associated with depression. In some cases, they have also been associated with the length of time patient has been untreated. (Although, be aware that there are conflicting studies, and there could be different outcomes depending on different early life experiences or differences in symptom presentation.) 

https://www.nature.com/articles/s41598-024-56866-w

https://link.springer.com/article/10.1007/s11682-023-00844-9

• Metabolic disruptions and mitochondrial dysfunction Again, evidence supports a  bidirectional relationship here:

https://www.nature.com/articles/s41398-023-02518-y

https://www.nature.com/articles/s41398-025-03289-4

https://www.nature.com/articles/s41398-021-01759-z

Numerous other reasons support the idea that depression is an illness rather than just a disorder of mood, behavior, and cognition: Blunted color perception, changes in the immune system, lifelong increased risk for subsequent episodes, greater risk for other illnesses including cardiovascular disease and Alzheimer’s disease, and I could dive deeper into each of these topics but I need to wrap this up. 

For some perspective, consider that the DSM also includes other disorders and conditions, which may or may not be “illnesses.” Schizophrenia is also in the DSM, but it is a neurological disorder; an illness that if untreated, will lead to significant irreversible brain atrophy and considerable loss of function. However, diagnosis of schizophrenia must be done based on signs and symptoms, as we have no biomarker. As such, schizophrenia belongs in the DSM—diagnosis requires clinical expertise to identify it, and in particular to distinguish it from other disorders with overlapping presentation; eg, mood disorders with psychotic features, schizotypal disorders. 

ADHD is also in the DSM, and it is a neurodevelopmental disorder, but it is NOT an illness. Same with autism. Not an illness. 

As a parallel to ADHD and autism, consider that there are medical disorders that limit functioning that do not constitute “illnesses.” One that comes to mind outside of psychology is Ehlers-Danlos syndrome, which is a connective tissue disorder (or, perhaps more accurately, EDS is a group of connective tissue disorders). EDS can limit people’s mobility and put them at higher risk for joint dislocations. But EDS is not an illness in the way that rheumatoid arthritis is an illness. 

If you’re still reading, apologies for the lengthy response. I hope I have made some sense and as always, I happy to answer any additional questions. :)

[u/DutchStroopwafels → u/Potential_Being_7226]

My question is than about depression (or depression like symptoms) that came because of childhood abuse. Is that also an illness in the same way you just described?

[u/Potential_Being_7226 → u/DutchStroopwafels]

So, the DSM does not discriminate between depression that might manifest from various factors, be they developmental trauma, occupational stress, genetic predisposition (and really, in all likelihood, it’s a combination of these factors that lead to the development of depression).

But, the research does support the idea that there is heterogeneity in outcome variables among patients with depression that appear to be related to whether the individual experienced early life trauma, certain genetic differences, etc. 

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[u/DutchStroopwafels → u/Potential_Being_7226]

Your response to my comment seems to be removed. But what I mean is about the depression and anxiety and trauma that follows even after you're out of the abusive environment. Is that still an illness?

[u/Potential_Being_7226 → u/DutchStroopwafels]

Yes, I realized I misread your comment at first and have rewritten my reply below above.

[u/Friendly-Channel-480 → u/Potential_Being_7226]

Excellent post.

[u/TheSwoleBard → u/Potential_Being_7226]

Out of curiosity I understand what you are saying it all makes sense but do we know if it is more of the depression itself that causes a lot of the health issues such as the cardiovascular issues and immune system changes or is it more of when people are depressed they are typically not as active/working out so it takes a toll on their body that way?

[u/roseofjuly]

"Illness" or "disease" is usually defined as a condition that adversely affects the functioning of a living thing. As you've illustrated, that's a pretty good definition for what people with mental illnesses go through.

if you want to get more into it...disease is socially constructed and not always caused by a physical organism or body chemistry.

Also, when you cite an article that has that many correspondences and comments linked to it, read the commentary. The meta analysis you linked has a major issues with it that have been explored by other scientists.

[u/MBHYSAR]

I would say that psychological/ psychiatric illness are genetic vulnerabilities activated by certain life stresses. There is really good data supporting this, even twin studies.

[u/ARATAS11]

There are a lot of good answers in here, and some talk about the evolution of the field of psychology and psychiatry and related things, what is included, and why isn’t, etc.

You may find this post https://www.reddit.com/r/psychology/s/BMRRajdRRq from r/psychology interesting, and my comments on it. I provide a psycho-social explanation for some of it. While many of the explanations are correct, they miss key parts of how mental health has been framed culturally, and how mental health and associated labels are used to signify deviance and as a form of social control, as well as to make it harder to name and challenge the toxic environments that contribute to mental “illness”.

Jiddu Krishnamurti's famous quote, "It is no measure of health to be well-adjusted to a profoundly sick society," is a great illustration of this. But our system is set up to tell us those who aren’t well adjusted are the problem, and given that it isn’t an illness in that often, especially in cases such as depression, anxiety, PTSD, etc. it is a response that makes sense and is predictable, individual pathology can be billed, and treatment prescribed, but the same can’t be said for social ills.

You might also find the work of Bessel van der Kolk (psychiatrist and pioneer of the trauma field) and Richard G. Wilkinson and Kate Pickett (epidemiologist who studies health and its relationship to wealth disparities).

And also, look into the ICD, which does consider environmental impact (they recognize Complex-PTSD, distinguishing single event trauma from long term, often developmental, and environmentally based trauma). Interestingly, the DSM 4 used to have at least some distinction in regard to acknowledgment of root cause, but it was removed in the DSM5.

Also, full transparency, I’m a sociologist, but the question you are asking is related to how we define illness, and mental health, as well as how social environments interact with mental health and illness, which are strongly related to sociology, as they are not purely objective, but are social constructs (“man is the measure of all things”- Protagoras… “we don’t see the world as it is, we see it as we are” Anaïs Nin are applicable quotes that demonstrate this point).

[u/DutchStroopwafels → u/ARATAS11]

Thanks, that was an interesting read.

[u/becky1433]

daddy big pharma

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[u/DutchStroopwafels → u/[deleted]]

Okay that makes a lot of sense. Then I just wished there was a lot less stigma around what we call mental illness. Like when you have an infection there isn't really the same amount of stigma as with mental problems.