So, Is It Your Hormones?

How hormones affect your brain and mood, why hormonal changes can feel surprisingly psychological, and what the science actually tells us.

19 minute read  ·  4,324 words

There are days when you seem to have considerably less patience for everyone. Or concentrating feels strangely difficult. Or you are unusually tearful, irritable, anxious, hungry, tired, restless, flat, or somehow all of these things at once.

Sometimes there is an obvious reason. You slept badly. Something happened at work. You have been under pressure for weeks. You are ill. Your relationship is difficult at the moment. Life is, occasionally, just being life.

And sometimes someone says the sentence that is supposed to explain everything:

Which raises a rather inconvenient question. What does that actually mean?

Hormones are often talked about as if they are tiny messengers carrying simple instructions around the body. Estrogen makes you feel good. Progesterone makes you sleepy. Cortisol makes you stressed. Testosterone makes you confident. Everything becomes very tidy, very quickly. The actual biology is considerably less tidy.

Hormones can influence the brain, including systems involved in mood, attention, memory, motivation, stress and sleep. But they do this through complicated interactions with receptors, neurotransmitters, other hormones, brain circuits, previous experience and the environment the brain happens to be operating in.

And the same hormonal change can be barely noticeable in one person and profoundly important in another. That last part turns out to be one of the most interesting things about hormones.

The brain is not separate from the rest of the endocrine system.

Imagine someone telling you that a particular chemical in your body has changed. You might reasonably expect something fairly obvious to happen. A chemical changes, therefore something changes. The difficulty is that the brain does not work like a row of light switches.

Hormones influence the brain by interacting with receptors and signalling systems that are distributed across different regions and circuits. EstradiolEstradiolThe main form of estrogen in the body during the reproductive years. When people say estrogen, estradiol is usually the hormone they mean., for example, interacts with estrogen receptors in the nervous system and can influence neurotransmitter systems including serotonin, dopamine and glutamate. These systems are involved in an enormous range of functions, including mood, motivation, learning, memory and reward.

This is one reason the phrase “hormones affect your mood” is technically true but scientifically rather unsatisfying. It is a little like saying that electricity affects your house. Yes. But which room? Through which circuit? Doing what? And under what circumstances?

The effects of hormones are not simply about whether a hormone is present or absent. They depend on the hormone, the receptor it interacts with, the tissues involved, the timing and pattern of exposure, and what else is happening in the system.

Estradiol is particularly interesting because it is not simply something the reproductive system sends to the brain from a distance. It acts as a neuroactive steroidneuroactive steroidA steroid, made in the body or in the brain itself, that changes how nerve cells behave. Many act quickly on receptors at the surface of the cell., and research has linked it to changes in several neurotransmitter systems and neural processes. Much of the mechanistic evidence comes from animal and laboratory studies, however, and translating those findings into everyday human psychological experience requires caution.

That distinction is worth keeping. There is a long road between:

Hormone level is not the same thing as hormone effect.

This is where the story becomes much more interesting. Suppose two people experience the same hormonal change. You might expect them to have broadly the same response. They don’t necessarily.

One person notices very little. Another becomes noticeably more irritable or anxious. Someone else mainly notices sleep changes. Another person notices nothing until they look back at several months of symptoms and realise there is a pattern.

This is not particularly mysterious once you stop thinking of hormones as instructions and start thinking of them as signals being interpreted by a biological system.

Receptors can differ. Neural circuits can differ. Previous exposure matters. Other hormones matter. Stress matters. Sleep matters. Genetics matter. The timing and speed of a hormonal change can matter too. The brain is constantly adapting to its environment, and hormones are part of that environment.

One of the clearest examples comes from premenstrual dysphoric disorder, or PMDD.

PMDD is characterised by recurring mood symptoms, including irritability, depressed mood, anxiety and emotional labilityemotional labilityMoods that shift quickly and strongly, often more than the situation seems to call for, such as sudden tearfulness or irritability., that are closely tied to the luteal phaseluteal phaseThe second half of the menstrual cycle, from ovulation to the next period, when progesterone rises. The first half, before ovulation, is the follicular phase. of the menstrual cycle. What makes it particularly useful for understanding hormones is that the problem does not appear to be simply an abnormal amount of ovarian hormone circulating in the blood. Research increasingly points toward an altered sensitivity to normal hormonal fluctuations.

In other words, the question changes from:

That is a much more sophisticated question. It also explains something that can otherwise seem strange. If ordinary hormonal fluctuations were inherently mood-damaging, we would expect most people to have severe psychological reactions to them. They don’t.

The existence of conditions such as PMDD tells us that individual sensitivity matters enormously.

The internet has made the menstrual cycle sound remarkably efficient.

Apparently, there is a follicular phase for productivity, an ovulation phase for confidence, a luteal phase for introspection and a menstrual phase for retreating into a blanket while refusing all administrative responsibilities. It is an appealing story. It is also much neater than the evidence.

One of the most useful recent studies here is a 2025 meta-analysismeta-analysisA study of studies. It pools the results of many separate studies of one question, which gives a steadier answer than any single study can. of menstrual-cycle effects on cognitive performance. The researchers examined 102 articles involving 3,943 participants and 730 comparisons across attention, executive functioningexecutive functioningThe mental skills used to plan, focus, switch between tasks, hold things in mind and hold back an impulse., intelligence, creativity, motor function, spatial ability and verbal ability. They found no robust systematic evidence that objective cognitive performance reliably changes across menstrual-cycle phases.

That is worth paying attention to because it pushes back against a familiar idea: Your cycle does not appear to switch your cognitive abilities on and off.

You do not become objectively less intelligent because your period is approaching. There is no evidence that the brain reliably follows a monthly timetable in which executive function disappears on Thursday and returns approximately three days later. Fortunately. It would make scheduling meetings considerably more complicated.

But there is an important distinction here. A lack of robust evidence for systematic changes in objective cognitive performance does not mean people are imagining every change they notice. Cognition is only one part of experience.

These things are not contradictory.

The experience of “brain fog” is more complicated than a cognitive test

When someone says: “I can’t think properly,” they may be describing several different things.

A standard cognitive test captures only some of that.

This distinction becomes particularly important during menopause, where subjective cognitive complaints can be substantial even when objective cognitive performance does not map neatly onto them. A 2025 systematic review and meta-analysis examining 24 studies and 5,629 participants found that subjective and objective measures of cognition do not necessarily correspond closely during the menopausal transition.

That is not an argument for dismissing subjective experience. Quite the opposite. It is a reminder that “cognition” is not one thing.

One of progesterone’s metabolites has an unusual relationship with the brain.

Progesterone tends to get described as the “calming” hormone. That is another example of a complicated biological process being turned into a personality adjective.

One reason progesterone is particularly interesting is that the brain does not simply receive progesterone as progesterone. The body metabolises it into other neuroactive steroids, including allopregnanolone.

Allopregnanolone interacts with GABA-A receptors, which are part of one of the brain’s major inhibitory signalling systems. GABA generally reduces neuronal excitability, helping regulate how strongly neural circuits respond. Allopregnanolone can enhance GABA-A receptor activity, which is one reason it has attracted so much attention in research on anxiety, stress, sleep and mood.

And this is where things get wonderfully inconvenient. A substance that can have calming effects does not necessarily make every person feel calm.

In susceptible individuals, changes in allopregnanolone can be associated with anxiety, irritability and other negative mood symptoms. Research into PMDD suggests that altered sensitivity to changing allopregnanolone levels and GABA-A receptor function may contribute to symptoms.

So the same general signalling system that can help regulate neural inhibition can, under different circumstances, become part of a very unpleasant experience. This is one reason PMDD is such a useful case study.

That is a very different story. It is also much closer to what neuroscience actually looks like.

The brain is responding to change, not simply to a number

One of the striking ideas in this field is that change itself can matter. A hormone can be present at a level the brain has encountered many times before, but the transition into or out of that level can still be biologically meaningful.

Think about temperature. Twenty degrees Celsius is not inherently stressful. But going from five degrees to twenty feels very different from going from thirty degrees to twenty. The number is the same. The transition is not.

Hormonal systems are obviously much more complicated than room temperature, but the analogy captures something important. Biological systems respond not only to absolute levels but also to changing conditions and adaptation over time. This may be one reason that hormonal transitions can feel particularly noticeable.

And it brings us to another system that is constantly paying attention to change: the stress system.

Sometimes “hormonal” and “psychological” are describing the same system from different directions.

Imagine that you have slept badly for three nights. You are already more irritable. Then something mildly annoying happens. On an ordinary day, you might shrug. Today, you are disproportionately furious about the way someone has loaded the dishwasher.

The dishwasher did not suddenly become psychologically significant. Your internal conditions changed. Hormones can be part of those conditions.

The reproductive hormone system and the stress system communicate with one another through overlapping biological pathways. Research examining menstrual-cycle effects on the stress response has found some evidence of cycle-related differences in cortisolcortisolA hormone released by the adrenal glands as part of the body stress response. It helps mobilise energy and follows a daily rhythm, highest in the morning. reactivity, although the effects are small and the evidence base remains limited. One 2023 systematic review and meta-analysis of longitudinal studies found slightly higher cortisol responses to acute stressors during the luteal phase compared with the follicular phase.

This is not enough to say:

That would be much too simple. The study itself highlights the need for better research, and individual differences are substantial.

But the broader idea is important. The stress system does not operate in isolation. Neither does the reproductive system. And neither operates independently of sleep, immune activity, metabolism, pain or the brain’s interpretation of what is happening.

This is why trying to divide experience neatly into “physical” and “psychological” can become misleading.

Which part caused the feeling? There may not be one answer.

This is also why context matters

Suppose two people experience the same premenstrual hormonal changes. One is sleeping well, has relatively little stress, feels secure in their relationships and has no significant physical symptoms. The other is sleeping four hours a night, is already anxious, is experiencing chronic pain and is dealing with a difficult situation at work.

It would be strange to expect the same internal experience. The hormones are not operating on an empty brain. They are entering an already complicated system.

This is perhaps the most useful way to think about hormonal effects:

Puberty, postpartum, perimenopauseperimenopauseThe years of transition before the final period, when cycles become irregular and hormone levels fluctuate. Menopause itself is dated to twelve months after the last period. and menopause are not just changes in hormone levels.

Some periods of life involve relatively large changes in reproductive hormones over a comparatively short period. Puberty is one. Pregnancy and the postpartum period are another. Perimenopause is another. These transitions can make the relationship between hormones and psychological experience much easier to notice.

After pregnancy, the biological environment changes very quickly

During pregnancy, reproductive hormones reach very high levels. After delivery, the hormonal environment changes dramatically.

It is tempting to turn this into a simple explanation for postpartum depression:

But postpartum depression does not work like that. A recent 2026 review describes postpartum depression as involving interacting endocrine, stress-system, neurotransmitter and immune mechanisms rather than hormonal withdrawal alone.

There is also sleep deprivation.

And the extraordinary experience of suddenly being responsible for a person who has absolutely no respect for your preferred sleep schedule.

The hormones matter. They are not the whole story. That distinction is important because biological explanations should not erase psychological or social ones.

Then there is perimenopause

This is where many people first encounter the phrase “brain fog.” It can sound vague until you experience it.

You are still capable of doing the work. You simply feel less cognitively fluent while doing it.

And unlike some of the more exaggerated claims about menstrual-cycle cognition, there is growing evidence that the menopausal transition can be associated with meaningful changes in cognitive experience.

A 2026 systematic review and meta-analysis of 26 studies involving 9,428 participants found poorer cognitive outcomes in perimenopausal compared with premenopausal groups, although the finding depended importantly on how reproductive stages were classified. The researchers also found differences between subjective reports and objective performance depending on the comparison being made.

A 2025 review similarly notes that brain fog, mood changes and sleep disruption are common complaints during the menopausal transition.

Sleep deserves particular attention here. Menopausal sleep disturbance is common, and reproductive hormone changes, vasomotor symptomsvasomotor symptomsHot flashes and night sweats. Sudden waves of heat caused by changes in how the body controls blood flow and temperature. and other biological and psychological factors can all contribute. Poor sleep, in turn, can affect attention, memory, emotional regulation and mood.

So when someone says: “My hormones have ruined my concentration,” the answer may be more complicated than either agreeing or disagreeing.

Hormonal changes may be contributing directly. They may also be changing sleep. They may be contributing to hot flashes or night-time waking. Those changes may then affect attention and emotional regulation. And stress about feeling cognitively different may add another layer.

The brain does not label each factor separately. It simply experiences the result.

Sometimes. But that answer is much less useful than it sounds.

Hormones are involved in the brain. They influence signalling systems, neural circuits and physiological states that matter for mood, cognition, stress and sleep. There is good evidence for that.

There is also good evidence that hormonal changes can affect people very differently. And that is where the phrase “it’s just your hormones” starts to fall apart. Because “your hormones” are not an explanation in themselves.

They are a biological system interacting with another biological system, which is interacting with your history, your environment, your sleep, your relationships, your stress level, your health and the meaning your brain is making of what is happening.

Sometimes the hormonal component is obvious. PMDD provides one of the clearest examples. The hormonal fluctuations themselves are ordinary, but the response to those fluctuations can be profoundly different in a susceptible person.

Sometimes the effect is much harder to separate. Perimenopausal brain fog may involve hormonal changes, sleep disruption, vasomotor symptoms, mood, stress and several biological processes happening at the same time.

And sometimes the answer really isn’t hormones. You may be exhausted because you are exhausted. You may be anxious because something genuinely difficult is happening. You may be struggling to concentrate because you have been under sustained cognitive load. You may be irritable because somebody has been annoying you for three weeks and your nervous system has finally filed the appropriate paperwork.

A hormonal explanation should add information. It should not replace curiosity.

There is another reason to be careful with hormonal explanations

Hormones have become a very attractive explanation for almost everything. They are invisible, powerful and complicated enough to sound convincing. This makes them perfect for internet certainty. But biological plausibility is not the same thing as proof.

For example, estradiol has many effects on neural systems, but that does not mean that taking estrogen will automatically improve mood or cognition. When researchers have examined menopausal hormone therapy and cognition in randomized trials, the overall picture has been mixed. A 2024 meta-analysis of 34 randomized controlled trials involving more than 27,000 participants found no overall effect of menopausal hormone therapy on cognitive domain scores, while some effects varied according to treatment formulation and timing.

This is a good example of how science should work. We can have a compelling biological mechanism. And then we still have to ask: What happens in actual humans?

Sometimes the answer is impressive. Sometimes it is modest. And sometimes the evidence simply isn’t settled yet.

What this means for you

Perhaps the most useful question is not:

That question leaves room for the rest of the system.

Those patterns are worth paying attention to. Not because every pattern proves a hormonal cause. But because timing is information.

If something repeatedly happens at the same point in a physiological cycle, that is useful information to bring to a qualified healthcare professional. A symptom diary can sometimes be particularly helpful because memory is not very good at reconstructing patterns after the fact.

And if mood symptoms are severe, persistent, frightening or interfering substantially with your life, “it’s probably hormones” should not be the end of the investigation. It should be the beginning of a better one.

There is something slightly reassuring about the complexity here. We tend to imagine that being psychologically stable means feeling essentially the same all the time. It doesn’t.

Your brain is a living system. It is constantly responding to sleep, light, food, illness, stress, relationships, memories, expectations, physical sensations and changes in the body’s internal chemistry.

Hormones are part of that conversation. And sometimes they can help explain why something that feels disproportionate on Tuesday feels entirely manageable again on Friday.

But they do not erase your psychology. They do not determine your personality. And they certainly do not mean that every difficult feeling can be dismissed with three words:

The more interesting truth is that biology and psychology were never really separate conversations in the first place.

Your brain is part of your body. Your body is constantly communicating with your brain.

And hormones are some of the messengers carrying information between the two.