Irregular periods: causes, PCOS, thyroid and what helps

Author: Jessica Lloyd
Senior Vulvovaginal Specialist Naturopath | BHSc(N) | ISSVD, ISSWSH, BSSM, ATMS

Last reviewed: July 7, 2026

Irregular periods (oligomenorrhoea) means your cycle regularly runs shorter than 21 days or longer than 35 days from the start of one period to the start of the next, or that periods come and go unpredictably, or go missing altogether. Most of the time, an irregular cycle is a sign that ovulation is happening only infrequently, and the two go hand in hand.

It is common. In one large community study of women of childbearing age, about 12 per cent had oligomenorrhoea¹. Common does not mean it should be ignored, though. An irregular cycle is your body flagging that something upstream, usually hormonal, is not quite right, and it is worth working out why rather than waiting it out.

The ‘menstrual cycle’ is counted medically from Day 1 of your period to Day 1 of your next period, though in some countries people say ‘cycle’ when they mean the bleed itself.

Symptoms of irregular periods

Very light pink or brown discharge, but no real period
Cramping and pain, but no bleeding arrives
You have stopped the pill, but your period has not come back
You are not pregnant
You had a pregnancy, but your periods did not return
You had COVID, and your periods did not return

When irregular periods are normal

When periods first start (menarche), it is usual for them to be irregular for a year or so while the cycle finds its rhythm.

In perimenopause, periods can be irregular for a few years, with heavier bleeding and sometimes two periods in a month.

When there is no period at all for three months in a row, that is called amenorrhoea, which is worth having looked at.

Causes of irregular periods

Ovulation is a delicate, well-choreographed sequence, and quite a few things can knock it off course. Thyroid function, stress levels, nutrient status and how much exercise you are doing all feed into it². When ovulation stumbles, the cycle behind it becomes irregular. Here are the usual suspects.

Excess androgens and PCOS

Testosterone and other androgens can interfere with ovulation and throw the cycle out. One of the most common reasons for an irregular cycle is polycystic ovarian syndrome (PCOS), where higher androgens and insulin resistance often travel together.

High prolactin

Hyperprolactinaemia (high prolactin) can cause irregular or skipped periods, low libido, tender breasts, headaches, acne, facial hair growth and vaginal dryness³.

High prolactin is sometimes confused with PCOS. Possible causes include thyroid problems, a benign pituitary growth, high oestrogen, some medicines (SSRI antidepressants, proton pump inhibitors for reflux, antipsychotics), under-eating, alcohol and stress.

Low thyroid (hypothyroidism)

When the thyroid is underactive and not making enough thyroid hormone, ovulation suffers and progesterone drops off, which shows up as an irregular cycle⁴.

A standard thyroid screen does not always tell the whole story, so it is worth seeing a practitioner for fuller testing rather than relying on a single TSH result.

Stress, under-eating and heavy exercise

Your body will quietly pause ovulation if it senses there is not enough fuel to run a pregnancy. Ongoing stress, undereating, rapid weight loss or a heavy training load can each switch the reproductive signal down, a pattern known as functional hypothalamic amenorrhoea⁵.

It is not a fault in your body, it is a sensible safety response, and it usually settles once the energy balance and stress load are addressed.

Weight and insulin

Carrying extra weight, particularly around the middle, is linked with irregular cycles too⁶. Body fat is hormonally active and can shift oestrogen and insulin signalling, which feeds back into ovulation. This overlaps a lot with PCOS.

Toxin and chemical exposure

Herbicides, pesticides, heavy metals, food preservatives, colours and additives, solvents, flame retardants and pollution can interfere with hormone signalling, and some of these endocrine-disrupting chemicals are associated with disrupted ovulation and irregular cycles⁷. Some people tolerate a higher chemical load than others before symptoms show up.

Gut health and the microbiome

The gut is more involved in hormones than it looks. A set of gut bacteria, the estrobolome, helps regulate how much oestrogen is recycled back into circulation versus cleared out⁸. An imbalanced gut microbiome can also affect nutrient uptake and drive inflammation, so keeping digestion happy is a genuine part of sorting out an irregular cycle.

Getting to the bottom of it

The first job is to work out why the cycle has become irregular and to rule out anything that needs medical attention. A doctor may examine you, take a swab to check for infection, and refer you to a gynaecologist if needed. (We do not do physical or internal exams ourselves, so that part is best done by your GP, a women’s-health clinic or a gynaecologist.)

Medical investigations can include blood tests, pelvic scans and ultrasounds, and occasionally a laparoscopy or hysteroscopy to look inside the pelvis. A doctor may offer the oral contraceptive pill or other medications to manage symptoms.

See your doctor sooner rather than later if you have periods more than three months apart, bleeding between periods or after sex, very heavy bleeding, sudden new irregularity, or you are trying to conceive.

A natural and root-cause approach

Alongside ruling out the serious stuff, the more useful long-term question is what is driving the irregularity in the first place. An integrative or naturopathic practitioner works from that angle, taking a full health history including your menstrual pattern, family history and genetics⁹, and looking for the contributing factors rather than only managing the bleed.

Depending on what turns up, support might include changes to diet and lifestyle, steadying blood sugar and insulin, easing the stress load, restoring thyroid function, improving the quality of the vaginal and gut microbiome, reducing chemical exposures where practical, and shoring up any nutrient gaps. Herbal medicine also has a long track record for irregular and absent periods, and a reasonable evidence base behind it¹⁰, though it is best done with a practitioner, and a missed period should always have pregnancy ruled out first.

If you want to see what your vaginal microbiome is actually doing, a comprehensive vaginal microbiome test is a good starting point, and you are welcome to book an appointment to work through the underlying picture.

Frequently asked questions

How many days between periods counts as irregular?

A cycle that is regularly shorter than 21 days or longer than 35 days, counted from the first day of one period to the first day of the next, is considered irregular. A cycle that swings widely from month to month, for example 20 days then 40 days, counts too.

Are irregular periods normal after stopping the pill?

It can take a few months for your own cycle to re-establish after stopping hormonal contraception. If your periods have not returned to a regular pattern after about three months, or have not come back at all, it is worth getting checked, as the pill can mask an underlying issue like PCOS or a thyroid problem.

Can stress cause irregular periods?

Yes. Ongoing stress, along with under-eating or heavy exercise, can turn down the reproductive signal from the brain and delay or stop ovulation. This is a recognised cause of irregular and missing periods, and it usually improves once the stress and energy balance are addressed.

Do irregular periods mean I cannot get pregnant?

Not necessarily, but irregular cycles usually mean ovulation is happening less often or less predictably, which can make conceiving harder and timing trickier. If you are trying to conceive, it is worth investigating the cause early rather than waiting, since many of the drivers are treatable.

This article is general information and not a substitute for personalised medical advice. If you are worried about your symptoms, or your periods are very irregular, absent or accompanied by other changes, please see an experienced practitioner.