Why scientists say mental illnesses may share common roots

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For decades, psychiatry has treated conditions like depression, bipolar disorder and schizophrenia as distinct illnesses, each with its own labels, treatment plans and drug combinations. A major new genetics study suggests those boundaries may be far blurrier than once thought.

Published this month in Nature, the research analysed psychiatric and genetic data from more than six million people worldwide. Its central finding is striking: many common mental health conditions appear to share the same underlying genetic drivers, suggesting they may stem from related biological processes rather than entirely separate causes, the New York Times reported.

The findings could eventually reshape how mental illness is diagnosed, and how patients are treated.

A shared genetic foundation

The researchers examined data from over one million people diagnosed with one of 14 psychiatric disorders, along with genetic records from more than five million people without such diagnoses. Instead of finding sharply distinct genetic signatures for each condition, they found extensive overlap.

Based on shared genetic patterns, the disorders clustered into five broad groups. These included internalising conditions such as depression, anxiety and post-traumatic stress disorder; neurodevelopmental conditions like autism and attention-deficit hyperactivity disorder; substance use disorders; compulsive conditions such as obsessive-compulsive disorder and anorexia; and a fifth group that included bipolar disorder and schizophrenia.

Bipolar disorder and schizophrenia, in particular, were found to share roughly 70 percent of their genetic risk factors.

What this means for treatment

The findings help explain why some medications work across multiple diagnoses. Antidepressants, for example, are often effective not only for depression but also for anxiety and PTSD. Rather than treating symptoms in isolation, the research suggests that targeting shared biological pathways could lead to more effective therapies.

Researchers also argue that a biologically informed approach could reduce the burden many patients carry when they receive multiple overlapping diagnoses, each requiring different medications.

One of the study’s authors compared the current system to diagnosing a patient with separate illnesses for a cough, sore throat and runny nose instead of recognising a single underlying infection.

Genes, brains and biology

The study identified 238 genetic variants linked across the 14 disorders. Many of these variants regulate brain functions, particularly those affecting how neurons transmit signals.

One hotspot on chromosome 11 stood out for its role in increasing risk across eight different conditions. That region includes DRD2, a gene that regulates dopamine and is the main target of many antipsychotic drugs. Dopamine plays a central role in mood, motivation, reward and cognition.

Limits and caution

Despite the scale of the study, researchers stress that genes are only part of the story. Life experiences, stress, trauma and environment still play crucial roles in shaping mental health.

Experts also note that most existing genetic data comes from people of European ancestry, limiting how widely the findings can be applied. Efforts are underway to expand genetic databases to include more diverse populations.

Some clinicians caution that while the study points toward shared biology, it does not mean all patients with the same diagnosis are biologically identical. This may explain why psychiatric medications often work for some patients but not others.

Will psychiatry change?

The findings arrive as preparations begin for future editions of the Diagnostic and Statistical Manual of Mental Disorders, the classification system used by doctors, researchers and insurers worldwide.

While experts agree the study strengthens the case for biologically informed psychiatry, few expect rapid changes. Diagnostic systems tend to evolve slowly, and genetic testing is not yet practical for everyday clinical use.

Still, many researchers see the study as a turning point. It suggests that psychiatry may be moving away from rigid labels toward a model that better reflects how the brain actually works.

As one senior psychiatrist put it, the next decade could bring more change to mental health care than the past century combined.