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Precision Psychiatry: Psychiatry’s Search for Personalized Treatment

Health Psychology
Elif Çakar Author: Elif Çakar
9 minreading time
Precision Psychiatry: Psychiatry’s Search for Personalized Treatment

When a drug is found to be “effective on average” in a clinical trial, does that mean it will work for you? The same outpatient clinic, the same day, two different patients. Both say they have felt “exhausted” in recent months, and both receive the same diagnosis: major depression. One describes no longer taking pleasure in anything and finding no reason to get out of bed in the morning. The other describes being unable to sleep at night, feeling constantly on edge, and struggling even with the slightest tension. On paper, yes, the same illness, the same diagnosis. But are they really the same? A perspective published in Nature Reviews Drug Discovery in August 2026 reopened one of psychiatry’s most fundamental assumptions: do people who receive the same diagnosis really share the same biology?

Precision psychiatry takes exactly this question seriously. The aim is not to give everyone a separate diagnostic label, but to test whether people within the same diagnostic group may be experiencing similar symptoms through different mechanisms. To this end, measures ranging from EEG to behavioral tasks, and from brain imaging to blood samples, are being used. In other words, if, in addition to symptoms, we also look at person-specific biological and behavioral markers when making a diagnosis, we may be able to better predict which treatment will benefit whom most. Each of these measures looks at a different layer of depression. Because EEG can capture the brain’s electrical response to a stimulus at the millisecond level, it can show, for example, how the brain reacts while processing a reward or a threatening image. Behavioral tasks aim to objectively measure processes such as reward learning, attention, and threat appraisal; they look not only at what a person says they feel, but also at what they do. Functional brain imaging can show how particular brain networks work, while peripheral samples such as blood can offer markers that may be related to disease processes or drug effects. In this way, an experience described in words in a clinical interview can be placed alongside a measurable mechanistic profile.

But the main difficulty that tempers the excitement begins here. Most of these studies show average differences between groups: for example, reward responses are, on average, weaker in a group with depression. Yet an average difference is not enough to say which group a single person belongs to or which treatment they will benefit from. There is a large gap between a statistically significant group difference and a reliable prediction for an individual. For a biomarker to enter the clinic, it must be replicated in different samples, give consistent results when measured again in the same person and, most importantly, actually improve treatment decisions.

Another distinction that should not be overlooked here is the difference between biomarkers that predict the course of an illness and those that predict treatment response. A biological indicator may point to the possibility that a person’s symptoms will worsen over time or that the illness is likely to recur. But this information alone does not explain which treatment would be more effective for that person. The first group is defined as prognostic and the second as predictive biomarkers. Here the distinction between the two concepts becomes important. Prognostic biomarkers provide information about how the illness will progress in the future, whereas predictive biomarkers help anticipate how a person might respond to a particular treatment. In other words, the first focuses on the future of the illness, the second on the likely effect of treatment in that person. For precision psychiatry, what matters most is being able to determine not only how the illness will progress, but which of the different treatment options will benefit the person most.

One of the areas where precision psychiatry comes closest to clinical practice is pharmacogenetics. This approach examines how a person’s genetic characteristics may affect how the drugs they use are metabolized in the body and how much exposure to the drug they have. In particular, differences in genes encoding enzymes involved in drug metabolism, such as CYP2D6 and CYP2C19, can change the rate at which some antidepressants are processed in the body. As a result, two people taking the same dose of a drug may have different drug levels and, consequently, different risks of side effects.

For example, some variations in the CYP2C19 gene can markedly increase or decrease the blood levels of drugs such as citalopram and escitalopram. This difference is not something to be underestimated in everyday clinical practice. In one person, the drug may be processed faster than expected and fail to reach adequate levels in the blood, while in another it may be processed slowly and accumulate. The first person may conclude that “the drug didn’t work,” while the second may experience side effects that are hard to tolerate. Guidelines published by international expert groups offer dose adjustments or alternative drug recommendations for certain gene variants. In other words, the promise of precision psychiatry does not remain on paper here; it reaches the prescription desk.

But one thing needs to be said plainly: pharmacogenetics predicts not whether a drug will do you good, but how your body will process it. These two are not the same thing. Carrying a drug at an ideal level in the blood does not mean that depression will respond to it. Indeed, the findings of studies examining whether pharmacogenetic-test-guided treatment improves depression outcomes are not consistent. Some show a limited benefit, while others show no significant difference. In other words, even the most advanced example of precision psychiatry in the clinic is, today, less a revolution than a cautious aid.

To understand the reasons for this, we need to widen the picture a little. Although depression looks like a single illness, many different processes may lie beneath the same label. The two patients we described at the start are exactly such an example. Moreover, genetics is only one part of the picture: sleep, stress, comorbid conditions, other medications, even whether the drug is taken regularly can change the outcome. There are obstacles on the research side as well. Samples are often small, findings are hard to replicate across studies, and most studies are conducted in particular populations. Yet the frequencies of gene variants can differ between communities. An approach developed in one population may not be applicable to another with the same reliability. Before it becomes “tailor-made for everyone,” precision psychiatry has to pass the test of being “fair for everyone.”

Even if the technical obstacles are overcome, a more fundamental question remains: can what is measurable replace what is meaningful? Biomarkers are valuable, but they do not take the place of a person’s story. Why someone feels “exhausted” (their losses, relationships, work, sleep, and the way they see themselves) cannot be read from a blood value or an EEG wave. In the best-case scenario, precision psychiatry does not eliminate the clinical interview; it adds a new layer of data to it. What a person tells and what is measured are placed side by side, and the decision is made by reading the two together. In the worst-case scenario, there is a risk of repeating an old mistake in a new form: reducing a person to a biological profile instead of to a diagnostic label.

So what is needed for precision psychiatry to pass this test? First, findings replicated in large and diverse samples. Then, a measurement that not only produces differences between groups but also gives consistent results in a single person. Most importantly, a demonstration that treatment decisions made with these measurements genuinely improve patients’ conditions. A single test will not carry this load. Complementary models will be needed, in which EEG, behavioral tasks, genetics, and clinical information are used together. This means time, data, and patience. Setting expectations correctly is also the work of science: we must keep asking “what does this give me?” of every new test that comes with the promise of “personalized treatment.”

This debate has a quiet gain as well. An antidepressant’s failure to work should not be read as the patient resisting or “not trying hard enough.” That two people respond differently to the same drug reminds us that biology itself is diverse. Even if precision psychiatry does not give everyone a definitive answer today, the fact that it has begun to acknowledge this diversity makes it possible to put curiosity in place of guilt in the treatment process.

Let us return to the beginning, to the two patients in the clinic. Most likely we will keep giving both the same diagnosis and starting them on a similar drug. One cannot take pleasure in anything; the other cannot sleep a wink at night. Precision psychiatry is trying to show, systematically, that the stories of these two people do not fit under a single label. Not yet a prophecy, but a direction. Perhaps the real question is not “which biomarker?” but when we will be ready to see the person who remains behind the average. When that day comes, even the best measurement will not replace listening; it will only show us more clearly what we should be listening for. And perhaps by then the question “why didn’t this drug work?” will have given way to a more human one: “What would be good for this person?”

Kaynakça

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Elif Çakar Elif Çakar
Elif Çakar has an academic background rooted in philosophy and psychology and is currently pursuing graduate studies in Management and Organizational Psychology at Marmara University. Her interdisciplinary approach to human behavior draws on perspectives ranging from individual experience and psychological processes to organizational structures and broader social contexts. Her professional experience spans human resources, talent management, and organizational processes across diverse corporate environments. Working at the intersection of theory and practice has shaped her interest in understanding individuals not merely as participants in professional life, but as complex subjects shaped by relationships, values, choices, and the social environments they inhabit. Çakar approaches psychology and philosophy not as separate disciplines, but as complementary ways of engaging with the complexity of human experience. Her intellectual perspective is also informed by the ethical and human-centered philosophy of İoanna Kuçuradi, whose approach has contributed to her understanding of the individual within broader philosophical and social contexts. This perspective informs her writing, where seemingly ordinary experiences often become starting points for deeper psychological and philosophical inquiry. Alongside her academic and professional work, Çakar continues to write and produce content on psychology. Her areas of interest extend from organizational and occupational psychology to interpersonal relationships, social psychology, and neuropsychology. Rather than reducing human behavior to a single explanatory framework, she explores the interplay between individual experience, social context, cognitive processes, and emotional life. For Çakar, psychology is not simply a body of knowledge to be transmitted, but an evolving field through which human experience, relationships, and the world we inhabit can be continuously reconsidered.