Adults
What sustained pressure does to the brain
Dr Tom Pennybacker, Consultant Psychiatrist and Medical Driector, The Chelsea Psychology Clinic
What prolonged stress does to the brain is, in many respects, more complex and more interesting than the public conversation tends to allow. The research points to measurable changes in brain structure and function: in how memories are formed, in how emotional responses are regulated, in how clearly and steadily a person is able to think. These are not abstract findings. They help explain something that many people notice but find difficult to account for, a quality of thinking that feels less settled than usual, a flattening of emotional range, and a sense that the brain is working harder for less.
This article aims to help those experiencing prolonged stress understand what might be happening.
The system was built for something different
The brain’s stress response is, at its core, a survival mechanism. When something registers as threatening, the hypothalamic-pituitary-adrenal axis (the HPA axis, in shorthand) activates, cortisol rises, and the body shifts into a state of heightened readiness. For something time-limited, this works rather well. Acute stress can, in fact, sharpen certain cognitive functions temporarily, including working memory and attentional focus.
The difficulty arises when that activation is sustained for long periods. When prolonged stress does not resolve, the HPA axis remains in a state of dysregulation. Cortisol levels stay elevated beyond what the system can tolerate well, and the brain begins to respond to that load in ways that are now reasonably well documented.
What changes, and how
The hippocampus, the region most closely involved in forming and consolidating memories, appears to be particularly sensitive to prolonged cortisol exposure. Research has found that sustained stress can reduce hippocampal volume over time, with associated difficulties in forming new memories, retaining information, and maintaining cognitive flexibility. This is likely part of what people are describing when they say their thinking has become less clear, or that they are struggling to retain things they would ordinarily hold without effort.
The prefrontal cortex, which handles planning, considered decision-making, and the regulation of emotional response, also shows functional changes under sustained stress. Its activity diminishes. Meanwhile, the amygdala, which processes threat and emotional reactivity, tends to become more dominant and less well-regulated by the prefrontal cortex. The practical consequence of this shift, for many people, is that responses become more reactive and less considered. Small things carry a weight they did not used to. The felt capacity to step back and think clearly can become less readily available.
There is also research suggesting that chronic stress disrupts white matter, the brain’s communication infrastructure, in ways that may affect the timing and efficiency of signalling between regions. This is a newer area of investigation and it would be overstating it to treat the findings as fully settled. But it sits within a broader picture suggesting that sustained pressure does not only affect how we feel. It affects, gradually and measurably, how the brain is organised. There is evidence that chronic stress may rewire the brain in ways that extend well beyond mood, and that understanding is still developing.
The connection to depression and anxiety
One of the things I find myself explaining in consultations fairly often is why a period of prolonged pressure and the onset of a depressive episode are not always as separable as people assume them to be.
The evidence here is reasonably robust. Sustained elevation of cortisol appears to suppress neurogenesis in the hippocampus, the ongoing production of new cells thought to play a role in mood regulation and cognitive flexibility. The neurotransmitter systems involved in mood and motivation, dopamine, serotonin, norepinephrine, are also disrupted by chronic stress in ways that map closely onto what clinicians recognise as depressive and anxiety presentations. The effects of prolonged stress on mental health are, in this sense, not simply emotional. They are neurobiological.
What this means, in practical terms, is that the line between ‘I am under a great deal of stress’ and ‘I am beginning to develop a clinical disorder’ is not always a clear one. Both things can be present at once. Understanding that the brain is being affected physiologically is not about medicalising ordinary difficulty. It is about having a more accurate picture of what might need attention, and when.
What this does not mean
It is worth being careful here, because this kind of information can tip in unhelpful directions.
Not everyone under sustained pressure will develop a psychiatric disorder. The brain is considerably more resilient than a reading of the research alone might suggest. Many of the changes described above appear to be at least partly reversible, particularly when the underlying conditions change and when someone receives appropriate support. The honest answer, as with most things in psychiatry, is that it depends: on duration, on severity, on what else is present, on what resources a person has around them.
What the evidence does argue against, fairly persuasively, is the idea that prolonged stress is simply something to manage through willpower. The brain under that kind of sustained load is not merely an inconvenienced brain. Something is happening in it and whilst we should not catastrophise it, we should take it seriously.
When a conversation might be useful
There is no clean threshold here, and I would be cautious about anyone who offered one.
What I tend to look for in a clinical conversation is duration and change. If someone’s thinking, emotional steadiness, or capacity to function has felt noticeably different for several weeks, and particularly if this extends to sleep, concentration, or a flattening of the things that ordinarily bring some pleasure or engagement, that is usually a signal that something more than ordinary stress is present and worth exploring properly.
The most useful question is often not ‘how stressed am I?’ It is closer to: ‘how different do I feel from the version of myself that existed before this started?’ That gap, if it is consistent and it persists, is usually what brings someone into the clinic.
I want to ensure that people know these are things that can be managed. So if things feel more pressing or you are finding it difficult to cope, speaking to someone is always a reasonable first step.
If you are concerned about the impact of prolonged stress on your mental health, our psychiatrists are available for assessment at the Chelsea Psychology Clinic’s Chelsea and Harley Street clinics, or online. You can get in touch here.
Dr Tom Pennybacker
18 June 2026
Dr Tom Pennybacker is a founder and medical director of The Chelsea Psychology Clinic. He qualified as a medical doctor in 1999, initially working in physical health before specialising in psychiatry. He went on to complete in-depth training in psychotherapy at the Tavistock Clinic, developing specialist expertise in combining psychological interventions with medication. Dr Pennybacker’s career has taken him through clinical leadership roles in the NHS, where he led a team delivering complex psychiatric and psychological care to individuals with severe mental disorders, and into private practice, providing assessment and treatment for a wide range of mental health difficulties.
