Why does depression so often arrive with anxiety? Why do trauma symptoms, substance use, and mood problems so frequently become tangled together? For many patients, receiving more than one psychiatric diagnosis can feel confusing and discouraging, leaving them to question if the first diagnosis was wrong or if they’re getting worse. But a large new study suggests another possibility: many psychiatric disorders overlap because some of their biological roots overlap, too.
In research published in Nature, the Psychiatric Genomics Consortium’s Cross-Disorder Working Group analyzed genetic data from more than 1 million people with a childhood- or adult-onset psychiatric disorder and about 5 million people without a diagnosis. The researchers examined 14 conditions and found that the diagnoses cluster into broader, partly overlapping families:
- Internalizing disorders: major depression, anxiety disorders, and post-traumatic stress disorder (PTSD).
- Schizophrenia and bipolar disorder.
- Compulsive disorders: obsessive-compulsive disorder (OCD), anorexia nervosa, and, to a lesser extent, Tourette syndrome.
- Substance use disorders: alcohol use disorder, nicotine dependence, opioid use disorder, and cannabis use disorder.
- Neurodevelopmental disorders: autism spectrum disorder, attention-deficit/hyperactivity disorder (ADHD) and, to a lesser extent, Tourette syndrome.
Some of the overlaps were striking. Major depression, anxiety disorders, and PTSD shared an estimated 90 percent of their genetic risk, while schizophrenia and bipolar disorder shared about 66 percent of their genetic markers.
The findings support what many clinicians already see in practice. Depression and anxiety often share processes such as rumination, avoidance, sleep disruption, threat sensitivity, and emotion regulation difficulties. PTSD can include depression, hypervigilance, irritability, and substance use as attempts to manage unbearable arousal. ADHD may coexist with anxiety or substance use, not because a person is careless or weak, but because attention, impulse control, reward sensitivity, and stress regulation all intersect.
Genetics, however, is not destiny. A genetic association does not mean a person is fated to develop a disorder. Environment, trauma exposure, relationships, discrimination, poverty, culture, sleep, physical health, and access to care all shape Mental health. The study tells us something important about population-level risk; it does not reduce any individual to their DNA.
The study also hints at future treatment possibilities. Disorders that clustered together genetically showed similarities in when certain genes were active during development and which brain cell types were implicated. For instance, internalizing disorders were linked more strongly with genes expressed in oligodendrocytes, while schizophrenia and bipolar disorder were more strongly tied to genes expressed in excitatory neurons. These findings are early, but they may guide future efforts to develop or repurpose treatments for conditions that commonly appear together.
For patients, the immediate takeaway is more human than technical: having multiple diagnoses is not a personal failure, and it does not mean your symptoms are “all over the place.” Comorbidity is common because the mind and brain do not organize themselves according to the chapters of a diagnostic manual.
For clinicians, the study reinforces the value of treating across categories. A patient with depression and anxiety may benefit from approaches that target shared processes rather than treating each diagnosis as a separate island.
But the research offers a useful shift in perspective. Mental disorders may be named separately, yet they often travel together because they share vulnerabilities. Understanding those shared roots may help reduce stigma, improve care, and remind us that people are more complex than any single label.
