PCOS Explained: Why Periods Stop, What Insulin Has to Do With It, and How Ovulation Is Restored

Periods that arrive whenever they feel like it. Hair appearing where it was not invited. Weight that will not shift however carefully you eat. And an appointment that ends with someone suggesting you lose a bit of weight and come back in six months.

That consultation happens thousands of times a week, and it misses what is actually going on — which is a hormone loop that can be interrupted, often with fairly ordinary measures.

📋 What actually has to be true

Diagnosis needs two of these three, with the other causes excluded.

🧪 What must be ruled out first

This section exists because these conditions look identical from the outside and two of them respond to a single tablet.

That third row — high prolactin — is the one worth pressing for, because it is common, frequently missed, and treated with a tablet that works well. The giveaway is breast discharge, which women often do not mention because it seems unrelated to a periods problem.

And the last row deserves attention of a different kind: symptoms appearing suddenly and progressing over months, rather than creeping in since the teens, is not the usual pattern here and needs assessing promptly.

🧬 Why insulin is the engine

Here is the loop that explains why the symptoms travel together, and why they are treatable.

Most women with this condition have insulin resistance — cells respond poorly to insulin, so the pancreas produces more of it to compensate. Importantly, this happens in lean women too, which is why "just lose weight" is both unhelpful and sometimes irrelevant.

High circulating insulin then does two things at once:

• 🏭 It tells the ovary to produce more testosterone. Insulin acts directly on the hormone-producing cells of the ovary
• 📉 It tells the liver to make less SHBG — the protein that binds testosterone and keeps it inactive. Less binding protein means more free testosterone, even when the total looks normal

The result is more active androgen, which stalls follicles partway through maturation. They do not grow to the point of releasing an egg, so they sit at the edge of the ovary — which is exactly what the scan is showing.

No ovulation means no progesterone, because progesterone is made by the structure left behind after an egg is released. That has two consequences: periods become unpredictable or stop, and the womb lining is exposed to oestrogen with nothing to balance it.

Which is why reducing insulin resistance — by any route — tends to improve all of it at once.

🩸 Why absent periods are a medical problem, not just an inconvenience

⚖️ What moves the needle without a prescription

The lifestyle advice here is unusually specific, and the target is smaller than people expect.

• 📉 Five to ten percent of body weight. That alone restores ovulation in a meaningful share of women who are carrying extra weight. Around five kilograms for someone at ninety. Not a transformation — a shift
• 🏃 150 minutes of moderate activity a week, plus resistance work twice weekly. Muscle is where glucose goes, so building it improves insulin sensitivity directly
• 🍚 Fewer refined carbohydrates and sugary drinks. There is no special PCOS diet; what helps is anything that lowers the insulin spike after meals. Mediterranean-style eating has the best evidence
• 🚶 Walk after meals, and break up long periods of sitting
• 😴 Sleep. Short sleep worsens insulin resistance, and sleep apnoea is considerably more common in this group than generally realised — see our guide to sleep apnoea
• 🚬 Stopping smoking, which worsens insulin resistance on top of everything else

One honest note on the weight advice: this condition makes weight harder to lose, which makes being told to lose it particularly grating. The mechanism is real, the effort required is genuinely greater, and a modest result here is worth more than the same result would be in someone without it.

💊 The treatments, sorted by what you want from them

There is no single treatment, because there is no single complaint. What is used depends entirely on the goal.

🥚 Clomiphene, in practical detail

Clofert (Clomiphene) is the long-established way of restarting ovulation. It works by blocking oestrogen receptors in the brain, so the brain reads oestrogen as low and increases the signal telling the ovary to mature a follicle.

• 📅 Taken for five days early in the cycle, commonly starting on day two to five of a bleed. If there is no bleed to start from, one is usually brought on first with a progestogen
• 📈 Usually 50 mg daily to begin, increased in later cycles if nothing happened
• 🥚 Ovulation follows in roughly seven or eight women out of ten. Pregnancy rates are lower than that, because ovulating is necessary rather than sufficient
• 🔍 It needs checking, not assuming. A progesterone blood test about a week before the expected period confirms whether ovulation actually occurred. Without that check, months can pass on a dose that is not working
• 🔢 Use is limited to about six ovulatory cycles, after which a different approach is considered rather than continuing

What to expect from it: hot flushes, mood swings and bloating are common and settle after the five days. Its anti-oestrogen effect can also thin the womb lining and dry cervical mucus, which occasionally works against the very thing it is prescribed for — one reason letrozole has largely overtaken it where both are available.

🔵 Where metformin fits

Glucophage (Metformin) attacks the loop at its source by improving insulin sensitivity. Lower insulin means less ovarian androgen and more SHBG, which is the whole mechanism running in reverse.

In practice it tends to deliver:

• 🔄 More regular cycles in a reasonable proportion of women, sometimes enough to restore ovulation on its own
• 📉 Improved metabolic numbers — which matters given the diabetes risk discussed below
• ⚖️ Modest weight change at most. It is not a weight loss drug and expecting that leads to disappointment

Effects build over three to six months rather than weeks. The gut side effects that make people abandon it are largely avoidable by starting at 500 mg once daily with the evening meal and climbing slowly.

🫀 What this means over decades

The reason this deserves attention beyond the immediate symptoms.

• 🩸 Type 2 diabetes risk is substantially raised, and it arrives earlier. Worth an HbA1c or glucose test at diagnosis and periodically after — see our guide to prediabetes and how to reverse it
• 🤰 Gestational diabetes and pregnancy complications are commoner, so pregnancies are monitored more closely
• 🔬 Endometrial changes from long stretches without a bleed, as above
• 🫁 Sleep apnoea, which is both commoner and more often missed in women
• 🫀 Fatty liver, which travels with insulin resistance
• ❤️ Cardiovascular risk factors — blood pressure and lipids are worth checking
• 🧠 Depression and anxiety occur at considerably higher rates here, and that is a feature of the condition rather than a personal failing. It deserves treating in its own right

None of these is inevitable, and the same measures that help the periods help all of them, which is the useful part.

📞 When to seek help

Worth an appointment:

• Fewer than eight periods a year, or gaps longer than three months
• Told you have PCOS without blood tests for thyroid and prolactin — ask for them by name
• Diagnosed on an ultrasound alone, particularly as a teenager
• Milk or clear discharge from the breast when not breastfeeding
• Hair growth or voice change appearing rapidly over months, which is not the usual pattern
• Trying to conceive for a year, or six months if over 35
• On clomiphene with no progesterone check to confirm it worked
• Bleeding between periods, after sex, or unusually heavy
• No glucose or lipid testing since diagnosis
• Snoring with daytime sleepiness
• Low mood or anxiety, which is common here and treatable
• Taking spironolactone and planning a pregnancy

❓ Frequently asked questions

📑 Sources and editorial

• International evidence-based guideline for the assessment and management of polycystic ovary syndrome, including diagnostic criteria, the role of ultrasound and its exclusion within the years following menarche
• Rotterdam consensus criteria requiring two of three features: ovulatory dysfunction, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology
• Guidance on exclusion of thyroid dysfunction, hyperprolactinaemia and non-classical congenital adrenal hyperplasia before diagnosis, and on features warranting assessment for Cushing syndrome or androgen-secreting tumours
• Literature on insulin resistance in polycystic ovary syndrome, including its occurrence in lean individuals, stimulation of ovarian androgen production and suppression of sex hormone binding globulin
• Evidence on lifestyle intervention and the restoration of ovulatory function with five to ten percent weight reduction
• Guidance on endometrial protection in chronic anovulation, recommended frequency of withdrawal bleeding, and endometrial hyperplasia and carcinoma risk
• Prescribing information for medroxyprogesterone acetate, including withdrawal bleed induction and endometrial protection regimens
• Comparative trial evidence for letrozole versus clomiphene citrate for ovulation induction in polycystic ovary syndrome, including live birth outcomes
• Prescribing information for clomifene citrate, including dosing, cycle timing, ovulation and pregnancy rates, multiple pregnancy risk, visual disturbance, antioestrogenic effects on endometrium and cervical mucus, and the recommended limit on treatment cycles
• Guidance on mid-luteal progesterone measurement to confirm ovulation, and on ovarian hyperstimulation syndrome recognition
• Evidence on metformin in polycystic ovary syndrome for menstrual regularity and metabolic outcomes
• Prescribing information and guidance for spironolactone in hirsutism, including antiandrogenic effects, contraception requirement, teratogenic potential and hyperkalaemia risk
• Prescribing information for cabergoline in hyperprolactinaemia
• Evidence on long-term cardiometabolic outcomes in polycystic ovary syndrome, including type 2 diabetes, gestational diabetes, obstructive sleep apnoea, hepatic steatosis and cardiovascular risk factors, and on the prevalence of depression and anxiety
• Related reading: prediabetes and how to reverse it, metformin side effects and how to avoid them, restoring the menstrual cycle, obstructive sleep apnoea
• Related products: Clofert (Clomiphene), Provera (Medroxyprogesterone), Glucophage (Metformin), Aldactone (Spironolactone), womens health category
• RXshop Editorial Team — reviewed by Anita Sharma, MD, FACOG — Obstetrician-Gynecologist