Biology is coming to psychiatry’s diagnostic manual, even as reliable biomarkers remain rare. The “bible” of clinical psychiatry—the DSM, short for the Diagnostic and Statistical Manual of Mental Disorders—is one of the most popular psychiatry reference books around the world. Clinicians use it to diagnose patients and scientists use it to guide research. Despite its wide impact, the DSM has never integrated biology in its diagnoses of mental illness. This omission was largely because the underlying biology of mental illness was too preliminary to be included in such a widely used clinical manual.

The most recent version of the DSM—the DSM-5, released in 2013—has attracted significant criticism from clinicians and researchers, including on how its lack of objective biological measures risks medicalizing human suffering and reducing the validity of psychiatric diagnoses. The American Psychiatric Association announced that it will release the next edition of the DSM in the coming years, and one of its major plans is to modernize the manual by introducing biology. I was a member of the DSM’s strategic committee between May 2024 and August 2026 and contributed to the subcommittee tasked with integrating neurobiology into the manual.

Researchers’ understanding of the biology of mental disorders is still slowly evolving. So my DSM colleagues and I decided to take a more nuanced approach to incorporate neurobiology into the diagnosis of psychiatric conditions. What are biomarkers? Biological factors are mechanisms that may be involved in the development of a disease but have not yet crystallized into something that can be quantifiably measured in the lab. These factors can be physiological, genetic, or biochemical. In contrast, biological markers—called biomarkers for short—are characteristics that can be objectively measured and used to evaluate a biological process, including how well someone is responding to a particular treatment.

Biomarkers can be collected through blood tests, imaging scans, and other methods that reveal factors associated with a specific disease. Biomarkers are widely used in medicine. For example, hemoglobin A1C levels are used to diagnose and monitor diabetes, cholesterol levels to determine cardiovascular risk, and CT scans to measure the size of a tumor. Why aren’t there biomarkers for mental illness? There are currently no scientifically valid biomarkers for any psychiatric condition, with the exception of certain proteins used to diagnose Alzheimer’s disease.