Hormones and the cycle

PMS

Also called: premenstrual syndrome, premenstrual symptoms

PMS (premenstrual syndrome) is the cluster of physical and emotional symptoms that show up in the 5 to 7 days before a period and resolve once bleeding starts. About 75 percent of menstruating women experience some PMS. Severe forms (PMDD) affect 3-8 percent and need different treatment. The bloating, cramps, mood and food craving symptoms have hormonal roots, progesterone falling sharply at the end of the luteal phase.

What's actually happening

In the second half of the menstrual cycle (the luteal phase), progesterone is high. As the period approaches, both progesterone and oestrogen drop sharply. The brain, gut and skin all respond to these hormonal shifts. Some people are more sensitive to the drops than others. Genetics, gut microbiome, stress, sleep and inflammation all influence sensitivity.

Common symptoms

  • Bloating and water retention.
  • Breast tenderness.
  • Cramps in the lower abdomen and back.
  • Mood swings, irritability, sadness.
  • Food cravings (especially salt and sugar).
  • Headaches or migraines.
  • Fatigue or insomnia.
  • Constipation, then often loose stools at the start of bleeding.
  • Acne flares 7 days before the period.
  • Symptoms peak 1 to 3 days before bleeding and ease within 1-2 days of the period starting.

Why the gut is involved

Progesterone slows gut motility, so transit time can lengthen by 1-2 days in the luteal phase. This causes the late-cycle bloat and constipation. Once the period starts, prostaglandins released by the uterus also affect the bowel, causing the loose stools many women get on day 1. Cycle-related gut symptoms account for a large fraction of what women interpret as 'IBS', patterns become much clearer with 2-3 months of cycle plus symptom tracking.

What helps

  1. Track 2-3 cycles to see your pattern. Most women are surprised how predictable it is.
  2. Lower-sodium evenings in the last week of the cycle. Cuts water bloat noticeably.
  3. Magnesium glycinate 200-400 mg in the evening. Best evidence for PMS of any supplement.
  4. Vitamin B6 50-100 mg daily. Modest but real effect on mood symptoms.
  5. 30 minutes daily aerobic exercise across the cycle reduces overall PMS severity.
  6. Caffeine and alcohol felt more strongly in the luteal phase. Cut back the last 7 days for sleep and mood.
  7. Combined hormonal contraception (pill, ring, patch) reduces PMS for many women by suppressing ovulation.
  8. SSRIs (fluoxetine, sertraline) for severe PMS or PMDD. Used continuously or just in the luteal phase. Effective in trials.
  9. CBT focused on cycle awareness can reduce the distress without changing the physical symptoms.

When to see a doctor

  • Symptoms severely disrupt work or relationships every cycle (likely PMDD).
  • Suicidal thoughts or self-harm urges in the luteal phase.
  • Cycle-related symptoms that don't resolve with the period (could be endometriosis or other gynae condition).
  • New severe PMS in your 40s, could be perimenopause.

Common questions

What's the difference between PMS and PMDD?
PMDD (premenstrual dysphoric disorder) is the severe end. It requires 5+ specific symptoms for most cycles in the past year, including marked depression, anxiety or irritability that significantly disrupts function. About 3-8 percent of menstruators have PMDD. Treatment is often SSRIs and/or hormonal options under specialist care.
Can diet really help PMS?
Yes, modestly. Lower sodium reduces water retention. Higher magnesium helps cramps and sleep. Higher fibre keeps the late-cycle constipation in check. Reducing alcohol and caffeine in the last week often improves mood and sleep more than expected. None of these are a cure, but the cumulative effect is meaningful.
Why is my PMS worse some months than others?
Stress, sleep debt, illness, and life events all amplify PMS. Cycles after travel, exam weeks, or after antibiotics tend to be worse. The pattern is the cycle; the amplification is your context.
Do supplements like Vitex / agnus castus work?
Some evidence for moderate PMS, especially breast tenderness. Trials are mixed but several show benefit over placebo. Not first-line, but reasonable to try if conventional measures aren't enough. Don't combine with hormonal contraception or fertility treatment without checking with a doctor.

Sources