What Is PMS?Symptoms, Causes and What the Research Says

If the week before your period feels like a different version of you shows up, with a shorter fuse, a bigger appetite, sore breasts and a body that holds water, you already know what PMS is. What is less obvious is where the line sits between ordinary premenstrual change and something worth talking to a clinician about, and which of the many things people suggest for PMS have actually been tested.

This article covers how PMS is defined, how common it is, what is thought to cause it, how it differs from the more severe premenstrual dysphoric disorder (PMDD), and what the clinical research says about calcium, vitamin B6, exercise, cognitive behavioral therapy and antidepressants. It is educational, not personal medical advice.

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How Doctors Define PMS

The American College of Obstetricians and Gynecologists (ACOG) describes PMS as physical or mood changes in the days before menstruation that happen month after month and affect a woman's normal life. The timing is what makes it PMS rather than something else.

To make the diagnosis, ACOG says an ob-gyn looks for symptoms that:

• are present in the 5 days before a period, for at least three menstrual cycles in a row,
• end within 4 days after the period starts, and
• interfere with some normal activities.

Because the pattern matters more than any single symptom, ACOG recommends writing down and rating your symptoms every day for at least 2 to 3 months, along with the dates of your periods. The NHS gives similar advice: keep a diary for at least two cycles and bring it to your appointment.

The diary also helps rule out conditions that overlap with PMS. ACOG notes that depression and anxiety are the most common of these, and that about half of women seeking care for PMS have one of them. The difference is that depression and anxiety tend to be present all month and get worse before a period, whereas true PMS clears once bleeding begins. For what is happening hormonally in that window, see our guide to the luteal phase.

How Common PMS Is

The answer depends on how strictly you define it. The Office on Women's Health at the US Department of Health and Human Services reports that over 90% of women say they get some premenstrual symptoms, and that as many as three in four say they have had PMS symptoms at some point in their lives. For most, the symptoms are mild.

Research using formal criteria gives a lower figure. A 2014 systematic review and meta-analysis in the Journal of Clinical and Diagnostic Research pooled 17 studies and estimated the worldwide prevalence of PMS at 47.8%, with a wide confidence interval (32.6% to 62.9%). Estimates ranged from 12% in France to 98% in Iran, a spread the authors attribute partly to different diagnostic tools and small samples. So "about half" is a reasonable summary, with the caveat that the number moves a lot depending on who is asking and how.

Common Symptoms of PMS

ACOG groups PMS symptoms into emotional and physical. The lists are long, and nobody has all of them.

Emotional and behavioral symptoms

• Low mood, crying spells, irritability or angry outbursts
• Anxiety, confusion or poor concentration
• Social withdrawal
• Insomnia, or sleeping and napping more than usual
• Changes in sexual desire

Physical symptoms

• Appetite changes and food cravings, often for sweet or salty foods
• Breast tenderness
• Bloating, fluid retention and short-term weight gain
• Headache
• Swelling of the hands or feet
• Aches, pains and fatigue
• Skin breakouts and gastrointestinal upset

The NHS adds that symptoms can change from cycle to cycle, which is one more reason a diary is more reliable than memory. ACOG also notes that some other conditions, including migraine, asthma, allergies and seizure disorders, can flare in the days before a period even when they are not caused by it.

If cramping pain during the period itself is your main complaint, that is usually dysmenorrhea rather than PMS. We cover it separately in why period cramps happen and what the evidence says helps.

What Causes PMS

The honest answer is that nobody knows exactly. PMS symptoms appear in the luteal phase, the roughly two weeks between ovulation and the start of the period, when progesterone rises and then, if there is no pregnancy, both progesterone and estrogen fall. The symptoms track those hormonal changes closely enough that the hormones are clearly involved.

What the research suggests, though, is that women with PMS do not have abnormal hormone levels. Instead, they seem to respond differently to normal levels. The NHS describes PMDD, the severe form, as linked to being very sensitive to changes in hormones, and to differences in inherited genes. Brain chemistry is part of the story too: the fact that antidepressants acting on serotonin reduce premenstrual symptoms (see below) points to serotonin signaling as one of the pathways involved, which may also explain the carbohydrate cravings and sleep changes many women notice.

Older ideas that PMS is caused by stress or personality do not hold up. The Office on Women's Health is explicit that stress and emotional problems do not cause PMS, though they can make it harder to cope with. For the hormones behind each phase, read the four phases of the menstrual cycle.

PMS or PMDD?

Premenstrual dysphoric disorder is the severe end of the premenstrual spectrum. ACOG describes it as PMS whose symptoms are severe enough to cause problems with work or personal relationships. The mood symptoms dominate: intense irritability or anger, mood swings, hopelessness, anxiety and difficulty concentrating, with the same strict timing as PMS.

PMDD became a full diagnostic category in the DSM-5, the manual psychiatrists use, in 2013. The 2012 American Journal of Psychiatry paper that made the case for that change estimated PMDD affects 2% to 5% of premenopausal women. The Office on Women's Health puts it at less than 5%. In other words, PMS is common and PMDD is not, but PMDD is far from rare.

The distinction matters because PMDD responds to specific care, including SSRIs and cognitive behavioral therapy, and because it can include suicidal thoughts. The NHS advice is unambiguous: if you have PMDD symptoms and are feeling suicidal, get emergency help. In the US, you can call or text 988 to reach the Suicide and Crisis Lifeline.

What the Research Says Helps

A great deal is sold for PMS. ACOG's own view is blunt: most products advertised for PMS have either not been tested or have not been proved to work. Here is what has actually been studied, with the quality of the evidence stated plainly.

Calcium

The best single trial in this field is a 1998 randomized, double-blind, placebo-controlled study in the American Journal of Obstetrics and Gynecology. Across 12 US centers, 497 women with moderate to severe PMS took either 1,200 mg of elemental calcium a day (as calcium carbonate) or a placebo for three cycles. By the third cycle, total symptom scores had fallen 48% from baseline in the calcium group versus 30% on placebo, and all four symptom clusters (negative mood, water retention, food cravings and pain) improved significantly.

Two caveats. The placebo response was large, so the gap between the groups is smaller than the 48% headline suggests, and the trial has not been repeated at the same scale since. A 2020 systematic review in the International Journal of Preventive Medicine found that most of the 14 studies it gathered pointed the same way, with lower blood calcium in women with PMS and improvement with calcium supplementation, but called for larger dose-response trials before drawing a firm conclusion. ACOG lists 1,200 mg of calcium a day as an option, and suggests calcium-rich foods such as yogurt and leafy greens.

Vitamin B6

A 1999 systematic review in the BMJ pooled nine placebo-controlled trials of vitamin B6 (pyridoxine) covering 940 women. The odds of improvement in overall premenstrual symptoms were roughly twice as high on B6 as on placebo (odds ratio 2.32 after removing one outlying trial, 1.57 with it included), and depressive symptoms improved too.

The authors were candid that most of the trials were of low quality and that no dose-response relationship was found. Their conclusion was that doses up to 100 mg a day are likely to help and that there is no reason to take more. That upper limit matters: high doses of B6 over long periods can cause nerve damage, so this is one to discuss with a clinician rather than buying the largest bottle.

Exercise

Regular aerobic exercise is recommended by ACOG, the NHS and the Office on Women's Health. The trial evidence is encouraging but weaker than the recommendations imply. A 2020 systematic review and meta-analysis in BJGP Open identified 15 randomized trials (717 women) of exercise programs lasting at least eight weeks. In the seven trials that could be pooled, women who exercised reported substantially lower global PMS symptom scores than controls (standardized mean difference −1.08). The authors flagged a high risk of bias in 13 of the 15 trials and very different results between studies. Their verdict: exercise may be effective for PMS, but some uncertainty remains.

ACOG's practical suggestion is at least 30 minutes of brisk walking, running, cycling or swimming on most days, done all month rather than only when symptoms arrive.

Cognitive behavioral therapy

CBT is a structured talking therapy that targets patterns of thought and behavior. A 2009 meta-analysis in Psychotherapy and Psychosomatics pooled nine randomized trials of psychological approaches to PMS, five of which tested CBT. Low-quality evidence suggested CBT reduced premenstrual anxiety and depression (effect sizes around −0.55 to −0.58) and the interference of symptoms with daily life, with roughly one woman in five benefiting who otherwise would not have. Simply monitoring symptoms had weaker support, and education alone did not appear to help.

The NHS lists CBT among the options a GP may suggest when lifestyle changes have not been enough. Its appeal is that the benefits appear to last after the sessions end, which is not true of most medications.

SSRI antidepressants

Selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine and sertraline are the most studied prescription option for moderate to severe PMS and PMDD. The 2024 Cochrane review included 34 randomized trials and concluded, with moderate-certainty evidence, that SSRIs probably reduce overall self-rated premenstrual symptoms (standardized mean difference −0.57 across 12 studies and 1,742 women). Taking them continuously worked somewhat better than taking them only in the luteal phase.

The same review was careful about harms. SSRIs roughly tripled the odds of nausea and about doubled the odds of insomnia, sexual dysfunction, dizziness and dry mouth, and 68% of the included trials were funded by drug companies. ACOG notes antidepressants can be taken for two weeks before symptoms begin or throughout the cycle, and that hormonal birth control may lessen physical symptoms without necessarily helping mood. Both are decisions to make with a prescriber.

The Evidence at a Glance

Everyday Habits and Traditional Approaches

Beyond the studied interventions, the mainstream advice is consistent and low-risk. ACOG suggests a diet rich in complex carbohydrates (whole grains, beans, lentils), calcium-rich foods, less salt, sugar and caffeine, and smaller, more frequent meals. The NHS adds regular sleep, less alcohol, not smoking, and stress-reducing practices such as yoga or meditation. None of these has strong trial evidence on its own; they are sensible habits that cost nothing.

Many cultures have long-standing ways of eating and drinking in the week before a period. In Chinese households, warm foods and teas built around ginger, red dates, longan and goji are traditionally taken around the cycle, and the premenstrual week is regarded as a time to keep the body warm and avoid cold or raw foods. Those practices come from a framework of blood and qi rather than hormones; the tradition also has formal recipes for the days before a period, chiefly Jia Wei Xiao Yao San for irritability and bloating and Wen Jing Tang where cramps and cold dominate, and the 2009 Cochrane review found too few good trials to judge them. The clinical evidence for the everyday foods is thinner still, but they are a gentle, food-based way of marking the week. We explain the tradition in how Traditional Chinese Medicine views the menstrual cycle and the ingredients in foods and teas traditionally taken around your period.

Whatever you try, the symptom diary is the tool that tells you whether it is working. Two or three cycles of daily notes will show you more than any single good or bad month.

When to Talk to a Clinician

Mild premenstrual symptoms that you can manage with habits and over-the-counter options do not need an appointment. The guidance from ACOG, the NHS and the Office on Women's Health converges on a few situations where you should book one:

• Your symptoms interfere with work, relationships or daily life, or lifestyle changes have not helped.
• Low mood, anxiety or irritability are present most of the month rather than only before your period. This may be depression or anxiety rather than PMS, and it responds to different care.
• You have severe mood symptoms, hopelessness or thoughts of harming yourself. This may be PMDD. If you feel suicidal, call or text 988 in the US, call 999 in the UK, or go to your nearest emergency department.
• You are considering vitamin B6 above 50 mg a day (the UK safe upper level), calcium alongside other medications, or any prescription option.
• Symptoms begin for the first time in your 40s, when perimenopause can mimic or amplify PMS.

Bring your diary. A clinician can confirm the pattern, check for thyroid problems or other overlapping conditions, and talk through the options above in the context of your own health.

Frequently Asked Questions

How many days before a period does PMS start?

PMS symptoms typically begin in the 5 days before a period and end within 4 days after bleeding starts. Some women notice changes up to two weeks before, from around ovulation, but for a diagnosis of PMS, ACOG looks for symptoms in the five days before a period across at least three consecutive cycles.

What is the difference between PMS and PMDD?

PMDD is a severe form of PMS in which mood symptoms such as intense irritability, anger, hopelessness or anxiety are strong enough to disrupt work and relationships. It affects an estimated 2% to 5% of premenopausal women, compared with roughly half who report PMS, and it is a recognized psychiatric diagnosis that responds to SSRIs and cognitive behavioral therapy.

Does calcium help with PMS?

The strongest evidence for any nutrient in PMS is for calcium. In a 1998 randomized trial of 497 women, 1,200 mg of elemental calcium a day cut total symptom scores by 48% over three cycles, compared with 30% on placebo. The placebo effect was large and the trial has not been repeated at that scale, so the benefit is probably real but modest.

References

1. American College of Obstetricians and Gynecologists. Premenstrual Syndrome (PMS). Frequently Asked Questions. ACOG

2. Office on Women's Health, US Department of Health and Human Services. Premenstrual syndrome (PMS). womenshealth.gov

3. National Health Service. PMS (premenstrual syndrome). Reviewed June 2024. NHS

4. Direkvand-Moghadam, A. et al. (2014). Epidemiology of Premenstrual Syndrome (PMS): A Systematic Review and Meta-Analysis Study. Journal of Clinical and Diagnostic Research, 8(2), 106 to 109. PubMed

5. Epperson, C.N. et al. (2012). Premenstrual dysphoric disorder: evidence for a new category for DSM-5. American Journal of Psychiatry, 169(5), 465 to 475. PubMed

6. Thys-Jacobs, S. et al. (1998). Calcium carbonate and the premenstrual syndrome: effects on premenstrual and menstrual symptoms. American Journal of Obstetrics and Gynecology, 179(2), 444 to 452. PubMed

7. Arab, A. et al. (2020). Beneficial Role of Calcium in Premenstrual Syndrome: A Systematic Review of Current Literature. International Journal of Preventive Medicine, 11, 156. PMC

8. Wyatt, K.M. et al. (1999). Efficacy of vitamin B-6 in the treatment of premenstrual syndrome: systematic review. BMJ, 318(7195), 1375 to 1381. PMC

9. Pearce, E. et al. (2020). Exercise for premenstrual syndrome: a systematic review and meta-analysis of randomised controlled trials. BJGP Open, 4(3), bjgpopen20X101032. BJGP Open

10. Busse, J.W. et al. (2009). Psychological intervention for premenstrual syndrome: a meta-analysis of randomized controlled trials. Psychotherapy and Psychosomatics, 78(1), 6 to 15. PubMed

11. Jespersen, C. et al. (2024). Selective serotonin reuptake inhibitors for premenstrual syndrome and premenstrual dysphoric disorder. Cochrane Database of Systematic Reviews, 8, CD001396. PubMed