PCOS & Irregular Periods

Kasi Subbiah
3 days ago
11 min read

PCOS, Irregular Periods and Endometrial Protection: What Actually Keeps the Womb Lining Safe?

A patient-friendly, evidence-based guide

Long gaps between periods are common in polycystic ovary syndrome (PCOS). They can seem like a minor inconvenience - or even a welcome saving on period products. Unfortunately, the womb lining does not always interpret a quiet calendar as a holiday.

In 2026, the NHS began using the new name polyendocrine metabolic ovarian syndrome (PMOS). This article retains PCOS for continuity with the rest of this treatment series; both names refer to the same condition.

When ovulation happens infrequently, the endometrium (the lining inside the womb) may be exposed to oestrogen without the regular progesterone signal that normally organises and sheds it. Over time, that can lead to erratic bleeding and, in some people, excessive thickening called endometrial hyperplasia.

The reassuring part is that this risk is usually manageable. Treatment does not have to produce a textbook 28-day cycle, and you do not necessarily need to bleed every month. The real goal is to make sure the lining is either shed at suitable intervals or kept thin continuously.

The short version: if PCOS is causing gaps of around three months or longer between spontaneous periods, or very few periods each year, discuss endometrial protection with a clinician. A combined hormonal contraceptive, planned courses of progestogen, a suitable progestogen-only method or a hormonal intrauterine system may be used. The best option depends on contraception, bleeding preferences, medical history and pregnancy plans.

Why periods become irregular in PCOS

A usual ovulatory cycle has two broad hormonal acts.

1. Before ovulation, oestrogen helps the endometrium grow in preparation for a possible pregnancy.

2. After ovulation, the emptied follicle becomes the corpus luteum and produces progesterone. Progesterone changes the lining from "keep growing" mode into a more organised, stable state. If pregnancy does not occur, progesterone falls and a period follows.

PCOS can disrupt follicle development and ovulation. If no egg is released, no normal corpus luteum forms and the expected progesterone phase may be missing. Oestrogen exposure can continue, but the lining does not receive its usual timing and tidying signal. The result may be a long gap with no bleeding, followed by spotting, prolonged bleeding or a period that arrives with the subtlety of an uninvited marching band.

This is called anovulatory bleeding. It is not simply a late version of an otherwise normal cycle.

What does "endometrial protection" mean?

Endometrial protection means reducing prolonged, unopposed stimulation of the womb lining. Clinically, this can be achieved in two ways:

· Periodic shedding: a prescribed course of progestogen is followed by a withdrawal bleed.

· Continuous suppression: hormonal contraception keeps the endometrium thin, whether or not a monthly bleed occurs.

This distinction matters. A person using a hormonal coil may have no periods because the lining is thin and quiet - which is protective. A person having no periods because they are persistently anovulatory and using no protective treatment is in a different biological situation. Same empty calendar; very different endometrium.

How worried should I be about endometrial cancer?

The 2023 International Evidence-based PCOS Guideline states that premenopausal women with PCOS have a markedly higher relative risk of endometrial hyperplasia and endometrial cancer. However, it also stresses that the overall chance of endometrial cancer remains low, so routine screening of everyone with PCOS is not recommended.

A 2023 meta-analysis of ten observational studies reported approximately fourfold higher odds of endometrial cancer in people with PCOS than in controls. That figure needs context: observational studies cannot completely separate PCOS from related factors such as body weight, diabetes and years without ovulation, and an increase from a low baseline risk can still mean a low absolute risk for an individual.

Risk deserves more attention when PCOS is accompanied by:

· long-standing untreated amenorrhoea (no periods);

· higher body weight;

· type 2 diabetes;

· persistent abnormal bleeding; or

· a persistently thickened endometrium found during an appropriate investigation.

The sensible response is prevention and symptom-led assessment, not an annual ultrasound "just in case". An ultrasound can suggest a thick lining, but endometrial hyperplasia is diagnosed with a biopsy, not by scan thickness alone.

When should treatment be discussed?

There is no single calendar rule that fits every age, medication and clinical situation. In an adult, the international guideline defines an irregular cycle as longer than 35 days, fewer than eight cycles per year, or any cycle longer than 90 days. In day-to-day practice, a gap approaching three months without a spontaneous bleed is a useful prompt to contact your clinician rather than waiting indefinitely.

Seek advice earlier if pregnancy is possible, the bleeding pattern has changed, bleeding is unusually heavy, or you have additional risk factors. Adolescents need age-appropriate assessment because irregular cycles can be normal in the first years after periods begin.

Before assuming PCOS is responsible, a clinician may consider:

· a pregnancy test;

· thyroid dysfunction or a raised prolactin;

· medication effects;

· perimenopause, depending on age;

· fibroids, polyps, cervical causes or other gynaecological conditions; and

· whether anaemia testing, ultrasound, hysteroscopy or endometrial sampling is appropriate.

PCOS is common, but it does not own every irregular bleed.

Treatment options at a glance

Option	What it does	Contraception	Bleeding Pattern	Suits someone who...
Combined pill, patch or ring	Supplies oestrogen plus progestogen; suppresses ovulation and keeps the lining controlled	Yes	Usually predictable withdrawal bleeding, or fewer/no bleeds with an extended regimen	wants contraception, cycle control and possibly help with acne or excess hair
Cyclic oral progestogen	Gives the lining a planned progesterone signal, usually followed by a withdrawal bleed	No	A bleed usually follows each course; timing and flow can vary	does not need contraception or cannot/would rather not use oestrogen
Progestogen-only pill or implant	Provides ongoing progestogen exposure and contraception	Yes	Bleeding may be absent, frequent or unpredictable	wants oestrogen-free contraception and accepts less predictable bleeding
Hormonal intrauterine system (IUS)	Releases levonorgestrel mainly inside the womb, strongly thinning the lining	Yes	Spotting is common initially; periods often become much lighter or stop	wants highly effective, low-maintenance contraception and strong local endometrial suppression
Progestogen injection	Suppresses ovulation and thins the lining	Yes	Irregular bleeding initially; no bleeding is common over time	values a three-monthly method after discussing weight, bone and fertility-return considerations

No table can screen for migraine aura, clotting history, blood pressure, breast cancer history, liver disease, unexplained bleeding or personal preferences. Method choice still requires an individual review.

1. Combined hormonal contraception

The combined oral contraceptive pill (COCP) is a first-line pharmacological option in international PCOS guidance for irregular cycles and/or hirsutism. The same broad principle applies to suitable combined patches and vaginal rings, although most PCOS-specific evidence concerns the pill.

Combined methods:

· provide reliable contraception when used correctly;

· prevent endometrial build-up by supplying progestogen and suppressing the natural cycle;

· usually make bleeding more predictable;

· may reduce acne and excess facial or body hair over time; and

· can be used in standard monthly cycles or, for many people, in tailored/extended regimens with fewer hormone-free intervals.

The bleed during a pill-free interval is a withdrawal bleed, not proof that ovulation occurred and not a monthly detox. There is no medical need to recreate a natural period every four weeks when a combined method is being used safely.

Who may need a different option?

Oestrogen-containing contraception is unsuitable for some people. Important examples include current or previous blood clots, certain clotting disorders, migraine with aura, some cardiovascular conditions, uncontrolled hypertension, and particular combinations of age and smoking. Other factors also matter, so eligibility should be checked against current UK contraceptive guidance rather than a social-media checklist.

The PCOS guideline does not identify one universally superior pill. It advises using general population contraceptive guidance, considering lower effective oestrogen doses, side effects and each person's metabolic and cardiovascular profile. Preparations containing 35 micrograms of ethinylestradiol plus cyproterone acetate are generally second-line because of thromboembolic risk.

2. Cyclic oral progestogen: protection without daily contraception

If contraception is not required, or oestrogen is not suitable, a clinician may prescribe a short course of an oral progestogen at planned intervals. Commonly used medicines include medroxyprogesterone acetate or norethisterone, although the drug, dose, number of days and interval must be prescribed individually.

After the tablets stop, the hormone level falls and a withdrawal bleed usually follows. The course does not "flush toxins" from the womb, restart the ovaries or prove that the next cycle will ovulate. Its job is more specific: it exposes the endometrium to progestogen and prompts an organised shed.

Advantages include avoiding oestrogen and taking tablets only intermittently. Limitations include:

· it is not contraception;

· the bleed may be heavy or inconvenient, particularly after a long gap;

· temporary bloating, breast tenderness, headache or mood effects may occur; and

· remembering each course requires a plan - calendars are excellent at birthdays and slightly less glamorous medical admin.

Do not start a withdrawal course without considering pregnancy if conception is possible. If no bleed occurs after a prescribed course, contact the prescriber rather than repeatedly self-treating.

3. The hormonal coil (levonorgestrel intrauterine system)

The hormonal IUS sits inside the womb and releases a small amount of levonorgestrel locally. It is one of the most effective contraceptive methods and produces strong endometrial suppression. Depending on the product and purpose, it may work for several years.

This is often an excellent option when the priorities are:

· dependable contraception;

· minimal daily effort;

· lighter periods or treatment of heavy bleeding; and

· continuous protection of the womb lining.

Irregular spotting is common in the first months. Later, periods may become very light or stop. Blood is not building up behind the coil: the progestogen keeps the lining thin, so there may simply be little to shed.

Insertion can be uncomfortable or painful. Pain-relief options, previous experiences, trauma-informed care and the option to pause should be discussed rather than treated as footnotes. An IUS will not directly treat PCOS-related excess hair and may not improve acne.

4. Other progestogen-only contraceptives

The progestogen-only pill, implant and injection can provide contraception while opposing or suppressing endometrial growth. However, PCOS-specific evidence is more limited, and bleeding patterns are less predictable than with many combined pills.

The international guideline says progestogen-only oral contraceptives may be considered for endometrial protection, based mainly on evidence from the general population. That honest wording matters: a recommendation can be clinically sensible even when dedicated PCOS trials are scarce.

With the pill or implant, irregular spotting is common. The injection may eventually stop bleeding, but it deserves a fuller discussion because some users experience weight gain, bone mineral density falls during use, and return of fertility can be delayed after the last injection. These are not automatic reasons to avoid it; they are reasons to choose it deliberately.

Do metformin, weight loss or Mounjaro protect the lining?

They may improve the biology driving irregular cycles, but they should not be mistaken for guaranteed endometrial protection.

Metformin can improve metabolic health and may make periods more regular in some people. The PCOS guideline allows it to be considered for irregular cycles when the combined pill is not accepted, tolerated or suitable. However, if long gaps continue, do not assume metformin is quietly doing the same job as a progestogen.

Lifestyle support and weight management, when relevant and approached without stigma, may improve insulin resistance and ovulation. The guideline includes weight management among preventive strategies for endometrial risk. Benefits can occur even without weight loss, and protection should never be withheld while someone works on metabolic goals.

Tirzepatide (Mounjaro) and GLP-1-based weight treatments may lead to weight loss and sometimes more regular ovulation as metabolic health improves. Tirzepatide is not an endometrial-protection medicine, and a more regular-looking calendar does not guarantee that every cycle is ovulatory. If gaps remain prolonged, use a specific protection plan.

Improved ovulation can also mean improved fertility. Anyone who could become pregnant needs contraception and medication-specific preconception advice. Tirzepatide can reduce the reliability of oral contraception during dose initiation and for four weeks after each dose increase; current product guidance should be followed, including use of a barrier method or a non-oral contraceptive during those windows.

What if I am trying to become pregnant?

Cycle suppression and fertility treatment have different jobs. If pregnancy is the goal, a combined pill, implant, injection or hormonal coil prevents conception while being used. Cyclic progestogen can protect the endometrium and create a withdrawal bleed, but it does not make the ovary release an egg.

For anovulatory infertility due to PCOS, the international guideline recommends letrozole as first-line pharmacological ovulation induction when there are no other infertility factors. Assessment may also include semen analysis, consideration of tubal testing, metabolic health, folate, blood pressure and a pregnancy-safe medication review.

There is no need to spend a year politely waiting for cycles that are clearly very infrequent before asking for help. A fertility plan can address ovulation while still protecting the endometrium between treatment cycles.

Do I need a monthly bleed?

Usually, no. What matters is the hormonal environment of the lining.

· On an effective hormonal IUS or suitable continuous hormonal contraception, no bleeding can be entirely expected because the lining remains thin.

· With untreated anovulation, no bleeding may mean the lining has had prolonged oestrogen exposure without regular progestogen.

· A monthly withdrawal bleed on the pill does not provide additional "cleansing" compared with an appropriately prescribed extended regimen.

This is why advice such as "you must bleed every month" is both catchy and biologically incomplete.

When bleeding needs prompt assessment

Arrange a clinical review if you have:

· bleeding between periods that persists or recurs;

· bleeding after sex;

· a new or substantially changed bleeding pattern;

· prolonged or very heavy bleeding;

· bleeding after a long period of amenorrhoea;

· symptoms of anaemia, such as breathlessness, marked fatigue, palpitations or dizziness; or

· any bleeding after menopause.

Seek urgent help for very heavy bleeding - for example, soaking through pads or tampons repeatedly - especially with faintness, severe weakness, chest pain, shortness of breath, severe pelvic pain or possible pregnancy. Ectopic pregnancy and significant blood loss need urgent exclusion.

A practical decision pathway

Step 1: Check the immediate questions

Could you be pregnant? How long has it been since the last spontaneous period? Is bleeding unusually heavy, painful, post-coital or between periods? Are there symptoms of anaemia?

Step 2: Decide whether contraception is wanted

This quickly separates two broad pathways. If contraception is wanted, consider combined or progestogen-only methods according to medical eligibility. If not, planned cyclic progestogen may be the simplest direct option.

Step 3: Decide what bleeding pattern you would prefer

Some people value a predictable withdrawal bleed. Others would happily unsubscribe from periods altogether. Both preferences are legitimate; method-specific safety matters more than menstrual virtue.

Step 4: Review medical eligibility and wider PCOS goals

Discuss migraine, blood pressure, smoking, clotting history, cardiovascular and metabolic risks, breast and liver conditions, mood, acne or excess hair, previous bleeding experiences and medication interactions.

Step 5: Agree a review point

Know what should happen if bleeding remains troublesome, no withdrawal bleed occurs, side effects persist or pregnancy plans change. A treatment plan is better when it includes an exit ramp.

Questions to take to your appointment

· Based on my bleeding pattern, do I need endometrial protection now?

· Do I need any investigation before starting treatment?

· Is oestrogen-containing contraception safe for me?

· Would cyclic progestogen or a hormonal IUS better match my priorities?

· If I choose cyclic progestogen, exactly when should I take it and when should I contact you if I do not bleed?

· Which symptoms should trigger ultrasound, hysteroscopy or biopsy?

· How will this plan change if I want pregnancy?

· Could my metabolic or weight medication make contraception less reliable?

The bottom line

In PCOS, irregular periods are not only a scheduling issue. Infrequent ovulation can mean the endometrium misses its usual progesterone signal, allowing prolonged and disorganised growth. PCOS increases the relative risk of endometrial hyperplasia and cancer, but the absolute cancer risk remains low and routine screening is not recommended for everyone.

Protection can be achieved by a regular prescribed progestogen withdrawal or by continuous hormonal suppression. The combined pill, cyclic oral progestogen, progestogen-only contraception and hormonal IUS each have different advantages. The best choice is the one that safely fits your need for contraception, preferred bleeding pattern, health history and pregnancy plans.

Most importantly, treatment is not about forcing the body to perform a monthly ceremony. It is about giving the womb lining a clear, reliable hormonal plan.