PCOS — polycystic ovary syndrome (a hormonal condition in which the ovaries produce an excess of androgens, the group of hormones often described as male sex hormones, and fail to release eggs regularly) — is the most common endocrine (hormone-related) disorder in women of reproductive age. It affects between 10 and 13% of women worldwide.[2]
Despite its name, polycystic ovary syndrome does not necessarily mean a woman has cysts on her ovaries. The term "polycystic ovarian morphology" (PCOM — see Key Terms) refers to a specific appearance on ultrasound — many small, immature follicles (fluid-filled sacs that each contain an egg) arranged around the edge of the ovary. Some women with PCOS have this appearance; others do not.
How PCOS is diagnosed — the Rotterdam criteria
PCOS is diagnosed using the Rotterdam criteria (a diagnostic framework agreed by international experts in 2003, used worldwide today). To receive a diagnosis, a woman must have at least two of the following three features:
- Oligo-ovulation or anovulation — infrequent or absent ovulation (release of an egg), typically presenting as irregular, infrequent, or absent periods
- Clinical or biochemical hyperandrogenism — evidence of excess androgen activity, either from symptoms such as hirsutism (excess hair growth in a male-pattern distribution — on the face, chest, or abdomen), acne, or scalp hair thinning; or from blood tests showing elevated androgen levels
- Polycystic ovarian morphology (PCOM) — the characteristic appearance of the ovaries on ultrasound, with 20 or more small follicles visible in one or both ovaries
Other conditions that can mimic PCOS must be excluded before diagnosis, including thyroid disorders, elevated prolactin (a hormone produced by the pituitary gland — a small gland at the base of the brain — that can suppress ovulation when elevated), and congenital adrenal hyperplasia (a rare inherited condition affecting the adrenal glands).
What is happening in PCOS?
The underlying mechanisms of PCOS are not fully understood, and research is ongoing. What is established is that PCOS involves disrupted signalling in the hypothalamic-pituitary-ovarian axis (HPO axis — the hormonal communication pathway between the brain and the ovaries that controls the menstrual cycle and ovulation). This disruption leads to elevated LH (luteinising hormone — a hormone that triggers ovulation, produced by the pituitary gland), which stimulates the ovaries to produce excess androgens. Eggs in the follicles do not mature fully or are not released.
Insulin resistance (see Key Terms) plays a central role in many women with PCOS. When the body's cells do not respond normally to insulin (the hormone that regulates blood sugar), the pancreas produces more insulin to compensate. This excess insulin further stimulates the ovaries to produce androgens, compounding the hormonal disruption. Insulin resistance in PCOS is not caused by weight — it occurs across the full range of body sizes and is part of the underlying biology of the condition.
PCOS and body weight: PCOS occurs in women of all body types. Around 20% of women with PCOS are of normal weight — what is sometimes described as "lean PCOS." Weight gain in PCOS is often a consequence of the underlying hormonal and metabolic disruption, not its cause. This distinction matters clinically: assuming PCOS is caused by weight can delay diagnosis in lean women and misframe management.
PCOS (Polycystic Ovary Syndrome)
A hormonal condition in which the ovaries produce excess androgens and ovulation is disrupted. One of the most common endocrine disorders in reproductive-age women.
Rotterdam Criteria
The internationally agreed diagnostic framework for PCOS. A diagnosis requires at least two of three features: irregular ovulation, hyperandrogenism, and polycystic ovarian morphology on ultrasound.
Androgens / Hyperandrogenism
Androgens are a group of hormones — including testosterone, DHEA-S, and androstenedione — present in all women but elevated in PCOS. Hyperandrogenism means excess androgen activity, producing symptoms such as acne, hirsutism, and scalp hair thinning.
Anovulation
The failure to release a mature egg (ovulate) during a menstrual cycle. In PCOS, anovulation is the main mechanism behind irregular periods and reduced fertility.
Insulin Resistance
A state in which the body's cells do not respond normally to insulin, requiring the pancreas to produce more to maintain blood sugar levels. In PCOS, excess insulin stimulates the ovaries to produce more androgens. Present in the majority of women with PCOS, regardless of weight.
Polycystic Ovarian Morphology (PCOM)
A specific ultrasound appearance of the ovaries — 20 or more small, immature follicles arranged around the edge of the ovary. One of the three Rotterdam criteria, but not required for diagnosis, and present in some women without PCOS.
AMH (Anti-Müllerian Hormone)
A hormone produced by ovarian follicles, used as a marker of the number of remaining eggs (ovarian reserve). AMH is often elevated in PCOS, reflecting the large number of immature follicles, and is increasingly used as a diagnostic marker.
Hirsutism
Excess hair growth in areas where hair is typically found in men — the face, chin, chest, and abdomen — caused by elevated androgens. One of the most common clinical features of PCOS.
Metformin (Glucophage)
A medication originally developed for type 2 diabetes that improves insulin sensitivity. Used in PCOS to address insulin resistance, reduce androgen levels, and support menstrual regularity. Recommended by international guidelines for PCOS metabolic management.
Letrozole (Femara)
An aromatase inhibitor (a medication that reduces oestrogen production, prompting the body to release more FSH and stimulate ovulation) used as the first-line treatment for ovulation induction in women with PCOS who are trying to conceive.
Inositol
A naturally occurring compound found in foods including fruits and grains, sold as a dietary supplement for PCOS. Myo-inositol and D-chiro-inositol are the forms most commonly marketed. Inositol is not a licensed medicine; evidence for its effects in PCOS is limited and it is not included in international clinical guidelines as a recommended treatment.
Anovulatory Infertility
Difficulty conceiving caused by failure to ovulate regularly. PCOS is the most common cause of anovulatory infertility, making it one of the leading reasons women are referred to fertility services.
1 in 10
women of reproductive age are estimated to have PCOS — making it one of the most common hormonal conditions seen in UK primary care.
[1]
No. 1
PCOS is the most common cause of anovulatory infertility — the most frequent preventable reason women are referred to fertility services.
[1]
~20%
of women with PCOS are of normal body weight — "lean PCOS." The hormonal disruption in PCOS occurs across all body types and is not caused by weight.
[2]
Life-long
PCOS is a life-long condition with consequences beyond the reproductive years — including significantly elevated long-term risks of type 2 diabetes, cardiovascular disease, and endometrial cancer.
[2]
Reproductive consequences
The most immediate impact of PCOS for many women is disrupted menstrual cycles — periods that are infrequent (fewer than eight per year), unpredictable, or absent altogether. Because ovulation is irregular or absent, conception can be more difficult. PCOS is the most common cause of anovulatory infertility worldwide.[1] However, infertility in PCOS is not absolute — the majority of women with PCOS who want to conceive are able to do so, often with appropriate management.
Metabolic consequences — insulin resistance and diabetes risk
Insulin resistance is present in the majority of women with PCOS, regardless of weight.[2] Over time, persistent insulin resistance increases the risk of developing impaired glucose tolerance (a state in which blood sugar is higher than normal but not yet at the level of type 2 diabetes) and type 2 diabetes. Women with PCOS are at significantly elevated risk of developing type 2 diabetes compared with women without the condition — a risk that exists regardless of BMI (body mass index — a ratio of weight to height used as a proxy measure of body fatness).[1]
Androgenic symptoms and quality of life
Elevated androgens produce symptoms that directly affect quality of life and self-image: hirsutism (excess hair growth — see Key Terms), acne, scalp hair thinning (androgenic alopecia — hair loss driven by androgen activity), and oily skin. These symptoms are often longstanding by the time a diagnosis is made, and many women describe years of managing them without understanding their hormonal cause.
Cardiovascular risk
The metabolic features of PCOS — insulin resistance, elevated androgens, and the obesity associated with some presentations — carry implications for cardiovascular health. Women with PCOS have higher rates of hypertension (raised blood pressure), dyslipidaemia (abnormal cholesterol and lipid levels), and the constellation of metabolic risk factors that increase the risk of heart disease. The 2023 International PCOS Guideline recommends cardiovascular risk assessment as part of PCOS management.[2]
Endometrial cancer risk
Because ovulation is infrequent or absent in PCOS, the lining of the womb (the endometrium — the inner layer of the uterus that is shed during menstruation) is not shed regularly. Without regular shedding, the endometrium can thicken over time — a process called endometrial hyperplasia (abnormal thickening of the womb lining) — which increases the risk of endometrial cancer. Managing menstrual regularity in PCOS is therefore not only about symptoms, but also about reducing this long-term risk.
Psychological impact
PCOS is associated with significantly higher rates of anxiety and depression compared with the general population.[2] The reasons are multiple: the visible symptoms (hirsutism, acne, weight changes), the fertility implications, the diagnostic delay that many women experience, and the condition's impact on self-image and relationships. Psychological wellbeing is a recognised dimension of PCOS management in international guidelines — not an afterthought.
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Diagnosis in practice
Diagnosis of PCOS is clinical — based on history and examination, supported by blood tests and ultrasound. The Rotterdam criteria (see Key Terms) require two of three features. In practice, a GP will typically ask about menstrual cycle pattern, symptoms of excess androgens (such as hirsutism, acne, or scalp hair loss), and any fertility concerns.
Blood tests used in the assessment of PCOS may include: testosterone (the main androgen measured clinically), LH and FSH (luteinising hormone and follicle-stimulating hormone — the pituitary hormones that drive the menstrual cycle), SHBG (sex hormone-binding globulin — a protein that binds androgens; low SHBG means more free androgen is active in the body), fasting blood glucose and/or HbA1c (glycated haemoglobin — a blood test that reflects average blood sugar over the previous two to three months) to assess metabolic status, and AMH (see Key Terms) where this is available. Thyroid function tests (measuring thyroid-stimulating hormone — TSH) and prolactin are checked to exclude other causes of the same symptom pattern.
Pelvic ultrasound (a scan of the pelvis using sound waves, typically performed via the abdomen or internally using a vaginal probe — a small, smooth device inserted gently into the vagina to obtain clearer images of the ovaries) is used to look for polycystic ovarian morphology. Ultrasound findings alone are not sufficient to diagnose PCOS — the criteria require two of the three Rotterdam features.
Note on hormonal contraception: Women using hormonal contraception — including the combined pill, progestogen-only pill, implant, injection, or hormonal IUS (intrauterine system — a small, T-shaped device inserted into the womb that releases a low dose of progestogen) — may have suppressed androgen levels and altered menstrual patterns that make PCOS harder to assess. Diagnosis in this context requires clinical judgement and, where appropriate, a period of time off hormonal contraception before definitive assessment.
Managing symptoms — the main approaches
First-line · Metabolic foundation
Lifestyle modification
For women with PCOS who are overweight, even modest weight loss — as little as 5–10% of body weight — has been shown to improve menstrual regularity, ovulation, androgen levels, and insulin sensitivity.
[2] Regular physical activity benefits insulin resistance independently of weight. These are recommended first-line approaches in international guidelines, not optional add-ons.
Hormonal treatment · Menstrual regulation
Combined oral contraceptive pill
The combined oral contraceptive pill (containing oestrogen and a progestogen — a synthetic or body-identical form of progesterone) regulates the menstrual cycle, reduces androgen production, and treats androgenic symptoms including hirsutism and acne. It is the most widely used pharmacological treatment for PCOS in women who do not want to conceive. It also protects the endometrium (womb lining) from the thickening that can occur with anovulatory cycles.
[2]
Metabolic treatment · Insulin resistance
Metformin (Glucophage)
Metformin (Glucophage) is a medication that improves the body's sensitivity to insulin. In PCOS, it reduces insulin levels, which in turn can lower androgen production and improve menstrual regularity. It is recommended by international guidelines for women with PCOS who have evidence of metabolic dysfunction — particularly impaired glucose tolerance or type 2 diabetes — and may be used alongside the combined pill or as an alternative where the pill is not suitable.
[2]
For fertility · Ovulation induction
Letrozole (Femara) or clomiphene (Clomid)
For women with PCOS who are trying to conceive and not ovulating regularly, ovulation induction (the use of medication to trigger the release of an egg) is a key part of fertility management. Letrozole (Femara — an aromatase inhibitor, see Key Terms) is now recommended as first-line treatment, having been shown to produce higher live birth rates than clomiphene (Clomid — a selective oestrogen receptor modulator that stimulates the pituitary to release FSH and trigger ovulation) in a landmark randomised trial.
[3]
Treating androgenic symptoms
Hirsutism, acne, and scalp hair thinning — driven by elevated androgens — are managed through a combination of hormonal and cosmetic approaches. The combined pill containing a progestogen with anti-androgenic properties (such as cyproterone acetate or drospirenone) is often preferred. Spironolactone (a diuretic — a medication that increases urine production — that also blocks androgen receptors) may be used in addition to hormonal contraception for women with significant hirsutism. Topical treatments, laser hair removal, and dermatological interventions are used alongside hormonal management. NICE has guidance on access to laser treatment for hirsutism for some women with PCOS.
Longer-term monitoring
Because of the long-term metabolic risks associated with PCOS, the 2023 International Evidence-based Guideline recommends regular monitoring of blood glucose and cardiovascular risk factors. This is particularly important in women who are overweight, have a family history of type 2 diabetes, or have additional metabolic risk factors. The frequency of monitoring is an individualised clinical decision.[2]
Three areas of evidence are particularly important for understanding PCOS management: the effectiveness of ovulation induction for fertility, the impact of lifestyle modification on hormonal and metabolic outcomes, and the scale of underdiagnosis in UK primary care.
Key finding
27.5%
live birth rate with letrozole
vs 19.1% with clomiphene — letrozole produces significantly higher live birth rates in women with PCOS trying to conceive
Legro RS et al · NEJM · 2014 · n=750 women with PCOS · randomised double-blind trial · 5 treatment cycles
Letrozole is superior to clomiphene for ovulation induction in PCOS
New England Journal of Medicine · 2014 · 371(2):119–129 · DOI: 10.1056/NEJMoa1313517
This landmark randomised controlled trial (a study where participants are randomly assigned to one of two treatments, to give an unbiased comparison) enrolled 750 women with PCOS and anovulatory infertility, assigning them to either letrozole (Femara — an aromatase inhibitor) or clomiphene (Clomid — a selective oestrogen receptor modulator) for up to five treatment cycles. The primary outcome was cumulative live birth rate. Women receiving letrozole had a live birth rate of 27.5% compared with 19.1% for clomiphene — a statistically significant difference (rate ratio 1.44). Ovulation rates were also higher with letrozole (61.7% per cycle vs 48.3% for clomiphene). There were no significant differences in congenital anomalies. This trial shifted international guideline recommendations: letrozole is now recommended as first-line ovulation induction in PCOS, replacing clomiphene as the standard of care.
Key finding
5–10%
weight loss
improves menstrual regularity, ovulation, androgen levels, and insulin resistance in overweight women with PCOS — recommended first-line in international guidelines
Teede HJ et al · 2023 Int'l Evidence-based PCOS Guideline · Human Reproduction · systematic review of lifestyle RCTs
Modest weight loss produces clinically meaningful improvements across multiple PCOS outcomes
Human Reproduction · 2023 · 38(9):1655–1679 · DOI: 10.1093/humrep/dead156 · PMID 37580314
The 2023 International Evidence-based Guideline for the Assessment and Management of PCOS (a guideline developed by an international network of specialist societies including ESHRE — the European Society of Human Reproduction and Embryology — and ASRM — the American Society for Reproductive Medicine — based on systematic review of the full body of clinical evidence) concludes that a modest weight loss of 5–10% of body weight produces significant clinical improvements across the spectrum of PCOS features in overweight women. These improvements include restoration of more regular menstrual cycles and ovulation, reduction in androgen levels, improvement in insulin sensitivity, and benefit to psychological outcomes. Lifestyle modification — combining dietary change and physical activity — is recommended as a first-line intervention before pharmacological treatment is considered. In women of normal weight with PCOS, regular exercise is recommended for metabolic and psychological benefit even when weight loss is not a goal.
Key finding
~2%
diagnosed in UK primary care
vs 10–13% expected prevalence — suggesting the large majority of UK women with PCOS remain unrecognised in primary care
Ding T et al · BMJ Open · 2016 · UK primary care data 2004–2014 · 7,233 women with confirmed PCOS diagnosis
PCOS is massively underdiagnosed in UK primary care — most women with the condition are not identified
BMJ Open · 2016 · DOI: 10.1136/bmjopen-2016-012461
This retrospective cohort study (a study that analyses existing medical records over time) examined UK primary care data from 2004 to 2014, identifying 7,233 women with a confirmed PCOS diagnosis and 7,057 with records suggesting probable PCOS. The recorded prevalence of PCOS in UK primary care in 2014 was approximately 2% — far below the internationally estimated true prevalence of 10–13%. This gap represents a large number of women living with an unrecognised condition and therefore not receiving appropriate management for its reproductive, metabolic, and psychological consequences. The study also showed significant variation in prescribing after diagnosis: only 15.2% of women with PCOS received a combined oral contraceptive prescription within 24 months of diagnosis, and only 10.2% received metformin. This suggests that even among diagnosed women, evidence-based management is inconsistently applied.
A note on the evidence base: Unlike many conditions, PCOS does not yet have a published NICE guideline — the NICE guideline for PCOS is in development and expected in November 2026. The authoritative international reference is the 2023 International Evidence-based Guideline for the Assessment and Management of PCOS, developed jointly by leading reproductive and endocrine societies worldwide. This is the guideline used by clinicians across the UK in the interim.
🔑 Putting it all together
PCOS is one of the most common hormonal conditions affecting women — and one of the most frequently misunderstood, both in the clinic and online. It is not a fertility problem that resolves once a woman has children. It is not caused by weight. It cannot be cured by diet or lifestyle, though both can meaningfully improve its features. And the treatments that have been demonised online — the combined pill and metformin — are, in fact, among the most evidence-based tools available for managing it.
The diagnostic delay many women experience — often years of symptoms before a name is given to what is happening — is a genuine failure of the system, not a reflection of the women themselves. PCOS is underdiagnosed, undertreated, and underresearched, particularly in the UK. The research evidence that exists is clear: modest lifestyle change helps, letrozole outperforms clomiphene for fertility, and metformin is safe and effective for metabolic management.
Every woman with PCOS is navigating a condition that affects multiple systems and extends across her whole life. Understanding what is known — and separating it from what the internet has invented — is the starting point. The detailed, individualised conversation about treatment belongs with a GP or healthcare professional.
About the author — Dr Paul spent over twenty years as an NHS GP before retiring in 2019. helf.school exists to give every person access to clear, honest, evidence-based health education.
Read more about Dr Paul →
References
1
NHS. Polycystic ovary syndrome (PCOS) — Overview. NHS website. Reviewed 2023.
2
Teede HJ, Tay CT, Laven JJE, Dokras A, Moran LJ, Piltonen TT, Costello MF, Boivin J, Redman LM, Boyle JA, Norman RJ, Mousa A, Joham AE; on behalf of the International PCOS Network. Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Human Reproduction. 2023;38(9):1655–1679. DOI: 10.1093/humrep/dead156. PMID: 37580314.
3
Legro RS, Brzyski RG, Diamond MP, Coutifaris C, Schlaff WD, Casson P, et al; NICHD Reproductive Medicine Network. Letrozole versus clomiphene for infertility in the polycystic ovary syndrome. New England Journal of Medicine. 2014;371(2):119–129. DOI: 10.1056/NEJMoa1313517.
4
Ding T, Baio G, Hardiman PJ, Petersen I, Sammon C. Diagnosis and management of polycystic ovary syndrome in the UK (2004–2014): a retrospective cohort study. BMJ Open. 2016;6(7):e012461. DOI: 10.1136/bmjopen-2016-012461.