What is PCOS?

PCOS, or polycystic ovary syndrome, is a long-term hormone condition that the NHS says "can affect hair growth, periods, fertility and mood". The 2023 International Evidence-based Guideline puts it at 10% to 13% of women of reproductive age, and the 2026 consensus paper in The Lancet says it affects one in eight women, with up to 70% of those affected undiagnosed.

Despite the name, PCOS is not a disease of ovarian cysts. The Lancet paper notes that although arrested follicle development is common, "pathological ovarian cysts are not increased". It is driven by hormones: raised androgens such as testosterone, insulin resistance, and changed brain signals to the ovaries.

For fertility, see trying to conceive with PCOS.

What is PCOS called now?

In May 2026 the condition was renamed polyendocrine metabolic ovarian syndrome (PMOS), and the NHS website has already switched. Monash University, which led the global consensus, says the clinical features, diagnostic criteria and management "remain unchanged", and both names will be used for three years. Why PCOS was renamed PMOS explains the change; this page says PCOS, the more familiar term.

What are the symptoms of PCOS?

The NHS lists the main symptoms as:

irregular periods or long gaps between periods
excess hair growth on the face or body (hirsutism), or hair loss
weight gain or difficulty losing weight
difficulty getting pregnant
depression or anxiety
oily skin and acne
feeling very tired
thick, dark patches of skin on the neck or armpits (acanthosis nigricans)

Symptoms usually start at puberty and can be mild, severe or absent, the NHS says, and they can have other causes. In the US, the American College of Obstetricians and Gynecologists (ACOG) says hirsutism affects more than 7 in 10 women with PCOS.

What causes PCOS?

The cause is not known. The NHS says it may be to do with hormones such as insulin and testosterone not working properly, and that you are more likely to have it if a close relative does or if you are from an Asian background. The Lancet paper puts insulin resistance at 85% of those affected, including 75% of those with a BMI of 25 or under. High androgen levels can stop the ovaries releasing an egg each month, ACOG explains. Higher weight makes the condition more severe, but the international guideline notes there is no consistent evidence that women with PCOS eat or exercise differently from women without it.

How is PCOS diagnosed?

Adults are diagnosed when two of three features are present, once other causes are ruled out. These are the 2003 Rotterdam criteria, refined by the 2018 and 2023 international guidelines; NICE Clinical Knowledge Summaries (CKS) use the same approach for UK GPs.

Criterion	What counts in adults	How it is checked
Irregular cycles or ovulation problems	Cycles shorter than 21 days or longer than 35 days, or fewer than 8 cycles a year (from 3 years after your first period)	Your period history
High androgens	Signs such as hirsutism or acne, or raised testosterone on a blood test	Examination and blood tests
Polycystic ovarian morphology	20 or more follicles in at least one ovary, or a raised anti-Müllerian hormone (AMH) level instead of a scan	Transvaginal ultrasound or an AMH blood test

If you have both irregular cycles and high androgens, the 2023 guideline says no scan or AMH test is needed. NICE CKS notes that polycystic-looking ovaries are not required, and do not establish the diagnosis on their own. The guideline says AMH should not be used as the only test for diagnosis (see what AMH tests can tell you). Teenagers need both irregular cycles and high androgens, with no scan or AMH, because acne and irregular cycles can be normal in the years after periods start.

Which blood tests check for PCOS?

Blood tests measure androgens and rule out look-alike conditions: the guideline's algorithm lists thyroid function (TSH), prolactin, 17-hydroxyprogesterone and FSH. The guideline calls routine insulin resistance tests inaccurate and does not currently recommend them. The combined pill makes androgen results hard to read; if testing is essential, the guideline says it is stopped for at least 3 months, using other contraception meanwhile.

What does PCOS mean for your long-term health?

The international guideline recommends a lifelong health plan, with these checks:

Risk	What the evidence says	Check the guideline recommends
Type 2 diabetes	Raised regardless of age and BMI; NICE CKS reports impaired glucose tolerance and type 2 diabetes at 3 to 5 times the usual rate, varying by region	Glucose check at diagnosis, then every 1 to 3 years depending on other risk factors
Heart and circulation	Higher odds of cardiovascular disease (1.68), heart attack (2.50) and stroke (1.71) (Lancet 2026), though overall risk before menopause is low	Cholesterol profile at diagnosis; blood pressure every year
Womb (endometrial) cancer	"Markedly higher" risk of womb-lining thickening and cancer, though the overall chance is low	No routine screening
Depression and anxiety	A 3.8-fold higher risk of depressive symptoms and 5.6-fold of anxiety symptoms, in a meta-analysis cited by NICE CKS	Screening for both in all adults
Sleep apnoea	More common, independent of BMI	Ask about snoring, waking unrefreshed and daytime sleepiness

NICE CKS links gaps of more than 3 months between periods to womb-lining thickening and later cancer, so mention it if yours are that far apart.

PCOS and pregnancy

The guideline treats PCOS as a high-risk condition in pregnancy. NICE CKS lists higher rates of gestational diabetes, pre-eclampsia, miscarriage and preterm birth. The guideline recommends considering a glucose tolerance test when planning pregnancy and offering one to everyone with PCOS at 24 to 28 weeks: see gestational diabetes.

How is PCOS treated?

There is no cure, so treatment targets the symptoms that matter to you. In outline, from the guideline and the NHS:

Healthy lifestyle for everyone, with benefits even without weight loss. Clinicians should ask permission before weighing you. See weight and fertility.
Irregular periods and excess hair: the combined pill is first-line. The NHS also lists the progestogen-only pill or a hormonal coil (IUS).
Metabolic health: metformin, mainly for metabolic features. Weight-loss medicines and surgery may be considered under general population guidelines.
Hair and skin: laser, creams, and anti-androgens if other treatment has not worked after at least 6 months; these need reliable contraception because they can affect a male baby's development.
Mental health: psychological therapy for depression, anxiety or eating disorders.
Fertility: for women who are not ovulating and have no other fertility problem, letrozole is the first-line medicine; see ovulation induction.

When to see a GP

The NHS advises seeing a GP if you think you might have PCOS, or if symptoms are affecting your everyday life, work or relationships; in the US, see your doctor or an ob-gyn. Bring your recent period dates (irregular periods explains what counts), notes on hair, skin and family history, and whether you use hormonal contraception.

Frequently asked questions

What is PCOS in medical terms?

PCOS is an endocrine (hormone) disorder diagnosed when two of three features are present: ovulatory dysfunction, hyperandrogenism, and polycystic ovarian morphology on ultrasound or a raised AMH level, after other causes are excluded. The 2026 Lancet consensus describes it as a multisystem condition with metabolic, reproductive, psychological and skin features.

What is the ICD-10 code for PCOS?

In the World Health Organization's ICD-10 classification, PCOS is coded E28.2, "Polycystic ovarian syndrome", under ovarian dysfunction. The new name has not yet been added: the Lancet consensus paper says formal engagement with the World Health Organization to bring PMOS into the classification is under way.

Is there a PCOS diet?

No single diet is proven best. The 2023 international guideline found no specific eating or exercise plan with benefits over others in PCOS, and recommends healthy eating and physical activity for everyone with the condition, whether or not they lose weight. It says inositol may be considered but has limited clinical benefits.

Does metformin help PCOS?

It can help metabolic features. The 2023 international guideline says metformin should be considered in adults with a BMI of 25 or over for weight, insulin resistance, glucose and cholesterol, and may be considered below that on limited evidence. It rates metformin above inositol for excess hair and waist size, with more stomach side effects.

What Is PCOS? Symptoms, Diagnosis and Long-Term Health