Scientists discover why mental disorders so often overlap

The Trouble With Mental Health Diagnosis

I always have reservations about any kind of diagnosis in mental health. Not because people do not struggle. They clearly do. But because mental health diagnosis is still built far more on reported symptoms, observed behaviour, checklists, and clinical judgement than on objective testing. The NHS describes a mental health assessment as a conversation, not a test or exam. Depression is mainly assessed by questions and questionnaires, and even for conditions like bipolar disorder, NIMH says there are no blood tests or brain scans that can diagnose it. Major reviews still say psychiatry lacks robust, reliable, valid biomarkers for most disorders.

That does not mean diagnosis is worthless. It does mean we should be honest about what it is. Systems like DSM-5-TR and ICD-11 were created to give clinicians a shared language and to improve consistency. They are classification systems. They describe patterns and thresholds that professionals are asked to evaluate. Even the World Health Organization frames ICD-11 as a tool to support more accurate and reliable identification in clinical settings, not as a lab-based proof of a distinct biological disease in the way people often imagine. WHO also now includes culture-related guidance and more dimensional approaches in some areas, which says a lot on its own: even the official systems recognise that people do not always fit into neat boxes.

This is where my concern really sits. Different diagnoses can share similar symptoms. People can meet criteria for more than one disorder at the same time. NIMH notes that different mental disorders may have overlapping symptoms, and that DSM diagnosis is often all-or-none: you either cross the threshold or you do not. Research on symptom profiles keeps raising the same problem. Two people can carry the same label and look very different, while two people with different labels can look surprisingly similar. That makes diagnosis feel less like hard science and more like an organised judgement call.

That also helps explain why opinions can differ from one mental health professional to another. The NHS explicitly says people can ask for a second opinion if they are unsure about a diagnosis. And even the DSM-5 field trials showed a mixed picture: some diagnoses had good to very good reliability, while others fell into questionable or unacceptable ranges. So yes, there is an attempt to make diagnosis more consistent, but the consistency is uneven, and that matters. It tells us these categories are not fixed truths waiting to be discovered under a microscope. They are clinical constructions shaped by thresholds, interpretation, context, and professional judgement.

Then there is the human part, which matters most. People are complex. Trauma, grief, poverty, culture, neurodivergence, relationships, physical illness, personality, and life history all shape how distress shows up. WHO’s own guidance now builds in cultural context because presentations differ across backgrounds. So when we talk about diagnosis, we should do it with a bit more humility. A label may sometimes be useful. It may open doors to support, language, and treatment. But it is still only one way of describing distress. It is not a clean scientific measurement of a person.

My own view is simple. I do not think mental health diagnosis sits comfortably inside the kind of science people often assume is behind it. At best, it is a framework. Sometimes helpful. Sometimes crude. Sometimes necessary. But still a framework. And when we forget that, we risk treating opinion as fact and categories as truth, when real people are always more complicated than the label put on them.

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