I’ve spent years studying PMS. Everything you’ve been told is wrong. This is the truth about why women’s behaviour changes before their period – and how you can really control it

It’s seen as being as much a part of being female as having breasts and two X chromosomes.

I’m talking about pre–menstrual syndrome (PMS), the toxic blend of physical, psychological and behavioural changes that can strike in the last two weeks of a woman’s menstrual cycle, just before her period – known as the luteal phase.

Usually, PMS heralds women feeling dreadful: irritable; anxious; tired; and assaulted by food cravings.

As part of my research, as a psychologist specialising in women’s hormones, I asked women about the last fortnight of their cycle. Two summed it up pithily: ‘inner scream’ and ‘everyone hates me’.

If men felt the way we do two weeks of the month, scientists would be working around the clock to solve their suffering. But for us it’s assumed as normal, simply our fate as women.

It’s estimated 75 to 90 per cent of reproductive–age women have PMS.

But it doesn’t make sense, from an evolutionary point of view, that it is just something we’re born with. Inherited traits that make people feel awful in their peak reproductive years usually get eliminated from the population over time, because they impinge on our ability to reproduce and survive.

It makes even less sense when you consider that the hormone at the heart of this, progesterone – vital for pregnancy and which rises in the second half of your cycle, while the other female sex hormone, oestrogen, drops – is supposed to make us feel good. Progesterone prompts the release of the neurosteroid allopregnanolone (also knon as allo), which has calming effects.

The more time I spent digging into the literature while working in my research lab at Texas Christian University in Fort Worth, the clearer it became that no one had answers for this contradiction.

Decoding the PMS mystery for my new book has been revelatory in how I view the female body.

Because it turns out that from our calorie consumption to how we view intimacy, there are scientific reasons for how we feel in the second half of our menstrual cycle – such good reasons that I don’t believe we should see PMS as a ‘syndrome’ at all.

It only feels like a syndrome because we do not respond appropriately to it with rest, good–quality nutrition and improved self–care.

Yet our changing needs in the last two weeks of our cycle have been ignored by science and medicine. This has led to the perception that PMS is almost akin to an illness. It should be viewed as the other half of our natural female state – when the body prepares for pregnancy.

Indeed, I was astonished to find there have been more than 200 ‘symptoms’ of PMS noted in the research literature. For example, among the symptoms of PMS are clumsiness, rashes and an increased sensitivity to pain.

The term PMS – first described as a medical problem back in 1931 – is nothing more than a lazy diagnostic catch–all.

Understanding this and taking steps to look after ourselves accordingly means our mood swings can be lessened, our energy raised and overall wellbeing enhanced.

Hormones aren’t ‘out of control’

Generally speaking, female hormones aren’t fickle or ‘out of control’, despite how certain men – even some women! – may perceive them.

You could almost set your watch to how regularly and distinctly different the luteal phase is to the first two (the follicular phase, when the body prepares for ovulation).

In the luteal phase, progesterone dominates. This is the forgotten female sex hormone – there are nearly three times as many research papers published on the effects of oestrogen compared to progesterone. This despite the luteal phase having more hormonal activity than the follicular.

Just before ovulation, oestrogen levels surge, increasing by 900 per cent. But this has nothing on the luteal phase, when progesterone levels rise by 2,400 per cent, before decreasing by the same magnitude if your period arrives. This is a lot of rapid hormonal change – which can lead to symptoms such as mood swings and bloating.

Yet most of us only hear about oestrogen. This bias has undoubtedly slowed the progress of research as our understanding of how women’s bodies respond to everything – from medication to anaesthesia – is incomplete (more of which later).

But you might fear a partner’s betrayal…

When progesterone surges, women often feel tired and unmotivated. Our body promotes these feelings on purpose, shifting us away from energy–hungry external pursuits (attraction! sex!) in preparation for the very internal, very costly pursuit of pregnancy. By prompting the release of the calming neurosteroid allo, progesterone makes our body less energetic and sleepier.

Allo also stimulates our brain’s receptors for the chemical messenger gamma–aminobutyric acid (GABA): this slows the brain and makes it less reactive.

This less gregarious state is perfect – potentially – for the earliest days of pregnancy. For some, however, this hormonal shift can register as low–key sadness.

Progesterone also increases our brain’s ability to detect possible sources of harm when we’re potentially most vulnerable to them – i.e. when preparing for pregnancy. This includes signs of threat to our relationship.

Research published in the journal Hormones and Behaviour in 2018 found that women in romantic relationships exhibit heightened abandonment fears in the luteal phase (which makes sense: the cost of having a partner leave when pregnant is high).

This is why it might not feel like a big deal if our partner stays late at work in the first two weeks of our cycle – but sets off alarm bells during weeks three and four.

One woman told me that during her luteal phase she interpreted the smallest slights, such as her partner not loading the dishwasher correctly, as harbingers of relationship doom.

Research published in the journal Evolution and Human Behaviour in 2014 showed that when progesterone is high, women are more likely to perceive negative emotions in people with neutral expressions than when progesterone is low.

These changes are guided by how our brain responds to progesterone. It increases the reactivity of the amygdala (our brain’s small, almond–shaped security system), lowering the bar on how threatening something has to appear before alarm bells ring.

Feed me now!

Many of us struggle with food cravings in our luteal phase – and really are hungrier at this time.

As a woman’s biology prepares for the demanding task of creating another person, our nutritional needs change.

Our heart rate, respiration rate and energy use while resting all increase in the luteal phase compared to the follicular – meaning we can burn up to 11 per cent more calories.

Yet we still follow nutritional ‘rules’, such as our usual calorie limit (i.e. 2,000 calories a day). You actually need an extra 140 to 175 calories daily to off–set the metabolic cost of this phase, the equivalent of about two boiled eggs or a small bowl of porridge with low–fat milk (more protein is also needed in the luteal phase to replenish essential amino acids which are depleted by high progesterone).

Secondly, progesterone increases appetite by decreasing insulin sensitivity, making our cells less responsive to glucose. This leads to blood–sugar fluctuations – and food cravings.

Yet women aren’t taught that it’s biologically normal to feel hungrier in their luteal phase – that it’s not just a lack of self control. It’s no coincidence that 2013 research in the Journal of Abnormal Psychology found that food craving, binge eating, disordered eating and emotional eating all peak in the luteal phase as we don’t give our bodies the nourishment they need.

Trusting our hunger is good for hormonal health. Fasting, calorie restriction and intense exercise without increasing calories, while fine for men, can wreak havoc on female sex hormones – and our sense of having PMS.

Sparks might not fly

You may feel there are fewer bedroom fireworks in your luteal phase. But while women are less sexually ‘turn–on–able’ at this time, rising progesterone changes the nature of our sexual motivations, from desire to needing to connect deeply to our partner – in case a baby is on the horizon.

In one study by the University of New Mexico, for instance, researchers followed 50 heterosexual couples and looked at changes in desire over the cycle based on how invested each partner was in the relationship.

They correctly predicted women who felt their partners were less invested would experience relatively high sexual desire and initiate sex at a high rate even as they moved into the luteal phase (when, as we’ve seen, women may be more anxious and more likely to have sex to keep the man involved).

Why health problems worsen

Many health conditions – including migraines, eczema, chronic fatigue syndrome, bladder pain, epilepsy, IBS, lupus, MS and diabetes – can become worse in the luteal phase, a little–known effect called premenstrual exacerbation (PME). When women aren’t told about this, it can create unnecessary anxiety.

For example, almost half of asthmatic women report worsening symptoms in the luteal phase.

Although the mechanisms responsible for these illnesses obviously differ, the impact is the same – worsening symptoms.

With asthma, for example, premenstrual worsening is the result of increased respiratory drive in the luteal phase, increasing breathlessness and worsening symptoms. But for women with IBS, worsening symptoms are the result of slowing gut motility.

I advise patients to track symptoms across their cycle so they know when they’re vulnerable to flare–ups, and to bring peace of mind that it’ll pass.

This sense of worsening health in the luteal phase is heightened by progesterone, making pain less tolerable.

It does this by changing the activities of brain chemical messengers known as neuropeptides involved in pain transmission.

This makes sense, as pain is something we experience to keep our body safe and, as far as evolution is concerned, there’s no better time to make sure your body is protected from harm than when pregnant or preparing to be.

There’s evidence that we respond differently to medication in the luteal phase, too.

Progesterone increases blood pressure, which can affect the rate prescription drugs are diffused throughout the body. This can change how long it takes to start working, how long it stays in circulation and its effectiveness.

For example, theophylline – used to manage asthma and COPD – is metabolised more slowly in the luteal phase, producing longer–lasting effects during the last two weeks of your cycle, according to a 2019 study published in Translational and Clinical Pharmacology.

Research from 2006 in the journal PACE also found progesterone’s natural sedative effects mean women’s anaesthesia needs may be reduced in the luteal phase.

And because progesterone dampens the inflammatory response needed for effective wound healing, it may suppress the ability to recover from surgery.

Yet there is very little research into all this. Almost no one is bothering to ask whether women’s hormones matter when it comes to drugs and other treatments because it’s so much easier to assume that they don’t.

Time to tame your ‘PMS’

To help your body during the luteal phase, you need to nurture it with unprocessed foods, exercise and plenty of sunlight. When your body is under so much hormonal pressure, self–care is imperative.

Some supplements can help (although always consult your GP first). Chasteberry, a centuries–old herb used to help women with reproductive health, was found to support symptoms of PMS in a 2019 study published in the journal Complementary Therapies in Medicine (as an anti–inflammatory, it may help hormone balance).

Magnesium supports progesterone production – I take a supplement, but magnesium–rich foods include most seeds, almonds, cashews, spinach, black beans, soy, brown rice, avocado and salmon. A review of studies in 2022 in the Journal of Obstetrics and Gynaecology Research found omega–3 supplements help women’s PMS–type moods, too (possibly by supporting serotonin production).

Tribulus terrestris, a plant used in Chinese traditional medicine to support sexual health, now has decent research – including from randomised, placebo–controlled trials – that indicates it may boost female sexual desire at times of hormonal change.

Adapted from The Period Brain by Dr Sarah E. Hill (Vermilion, £16.99). © Sarah Hill 2025. To order a copy for £15.29 (offer valid to 01/11/25; UK P&P free on orders over £25) go to mailshop.co.uk/books or call 020 3176 2937.