Letrozole experiences for PCOS and fertility

Letrozole (brand name Femara) is an aromatase inhibitor that is now first choice in many Dutch clinics for inducing ovulation in PCOS. You usually take 2.5 mg a day for 5 days, starting on cycle day 3. Letrozole experiences are strikingly often about what does not happen: fewer hot flushes and less trouble than expected.

That the drug is officially a breast cancer medicine puts many women off when they read the leaflet. Understandable, and it is exactly why this piece explains how completely different the dose and duration are here.

What is letrozole and how does it work for fertility?

Letrozole inhibits aromatase, the enzyme that converts androgens into oestrogen. Your oestrogen level therefore drops temporarily. Your pituitary notices and releases more FSH, and that FSH grows a follicle in your ovary until ovulation follows.

The end result resembles clomiphene, but the route differs fundamentally. Clomiphene blocks oestrogen receptors for weeks, including in your womb lining. Letrozole lowers oestrogen briefly and leaves your body fast, with a half-life of about two days.

Your oestrogen level therefore recovers in time to build the lining. That is the main theoretical reason letrozole works out better in PCOS, and it lines up with what the studies show.

Letrozole or clomiphene: what does the research say?

The comparison between the two is one of the best studied questions in fertility medicine. The headline is that letrozole leads to a live birth more often in PCOS, with fewer multiple pregnancies.

Those percentages come from the trial by Legro and colleagues in the New England Journal of Medicine (PMID 25006718), which randomised 750 women with PCOS. A 2022 Cochrane review of aromatase inhibitors in PCOS pointed the same way (PMID 36165742), as did an earlier meta-analysis (PMID 26479460).

Letrozole dose and schedule

The schedule closely resembles clomiphene: 5 days of tablets, starting around cycle day 3. If you respond insufficiently, the dose is raised in a following cycle. Your doctor tracks follicle growth by ultrasound.

Usual steps are 2.5 mg, then 5 mg, then 7.5 mg a day, each for 5 days in a row. If you have no spontaneous period, your doctor induces one first. These doses come from Dutch hospital protocols and the Farmacotherapeutisch Kompas.

Important: the doses and duration in breast cancer are entirely different, namely 2.5 mg a day for years. For ovulation induction you take it 5 days per cycle. The leaflet does not make that comparison for you, and that causes needless alarm.

Letrozole experiences: what do users report?

What stands out most in the stories is how uneventful many women find it. Women who used clomiphene before almost always name the same difference: fewer hot flushes and a clearer head.

What comes back positively:

• Noticeably fewer hot flushes than with clomiphene
• Fewer mood swings, more often described as manageable
• Cervical mucus keeps feeling more normal
• Often ovulation already at the lowest dose

What women find difficult:

• Tiredness on the days they take it
• Headache, usually mild
• Dizziness or a light-headed feeling
• Tender ovaries around ovulation
• Worry about the leaflet, which is about breast cancer

Picture two women of 30 with PCOS switching from clomiphene to letrozole. One ovulates at 2.5 mg and mainly notices the hot flushes are gone. The other only ovulates at 5 mg, with a progesterone of 42 nmol/l around day 21 confirming it. The same drug, two doses, ovulation in both.

Side effects of letrozole

The side effects reported most during a brief course are tiredness, headache, hot flushes and dizziness. They are usually mild and confined to the days of the course and just after, because the drug is broken down quickly.

Compared with clomiphene, women report fewer hot flushes on average, though this difference is not always as large in studies as it is in the stories. Joint complaints and bone thinning, which matter with long-term use in oncology, are not a relevant theme at 5 days per cycle.

Contact your doctor about persistent abdominal pain, a rapidly swelling abdomen or breathlessness, as these can point to ovarian overstimulation. That is rare with tablets, but not impossible.

Letrozole and pregnancy: is it safe?

This is the question nearly every woman asks, and rightly so. You take the drug in the cycle you hope to conceive in, so you want to know whether it can affect the embryo.

The short half-life is the reassuring part here: letrozole is largely out of your body before any fertilisation happens. In the large comparative trials, no higher rate of congenital abnormalities was seen in the letrozole group than in the clomiphene group (PMID 25006718).

Even so: you stop as soon as a pregnancy is confirmed, and you do not continue it during pregnancy. Always discuss your own situation with the doctor prescribing it. To understand what happens in those first weeks, read about hCG levels in early pregnancy.

Which values are tracked?

As with clomiphene the ultrasound leads, with blood values filling in. Progesterone around day 21, or about 7 days after the presumed ovulation, confirms whether ovulation really happened.

Beforehand, doctors often look at AMH for your ovarian reserve, at LH and FSH for the signalling, and at TSH, prolactin and insulin sensitivity to rule out other causes. With PCOS, insulin belongs firmly in that list.

You can have your AMH tested for an impression of your ovarian reserve, with an assessment by a BIG-registered doctor. Our guides to PCOS testing: which hormones and blood values and confirming ovulation with a blood test explain which values are useful when.

Alternatives and additions

Letrozole rarely stands alone. In PCOS it often works better alongside attention to insulin sensitivity and weight, because those two directly influence ovulation.

• Clomiphene, still a good option and the only licensed drug for this indication
• Gonadotrophin injections when tablets do not work well enough
• Metformin, sometimes added with clear insulin resistance
• Lifestyle and nutrition, see nutrition with PCOS and insulin resistance in women

What strikes us: women often get the prescription but not the explanation about insulin sensitivity. Yet that is the part you can influence yourself, alongside the course. See also our broader guide to PCOS diagnosis and modern management.

Frequently asked questions

How quickly do you conceive on letrozole?

Most pregnancies happen within the first three to six ovulatory cycles. In the NEJM trial the live birth rate after a maximum of five treatment cycles was 27.5 percent. If it does not happen, discuss with your doctor whether another route makes more sense.

What are the side effects of letrozole in PCOS?

Tiredness, headache, hot flushes and dizziness are reported most, usually mild and limited to the course days. Women who used clomiphene before often experience the hot flushes as milder. Serious complaints are rare on this short schedule.

Which day do you start letrozole?

Usually on cycle day 3, taking it for 5 days in a row. Some protocols choose day 2 or day 5 as the starting point. Follow the schedule your own clinic uses, because the scan appointments are set around it.

Why does the leaflet mention breast cancer?

Letrozole is licensed to treat breast cancer after menopause, and the leaflet describes that use. For fertility it is used off-label at a completely different dose and duration. That context is missing from the leaflet, which understandably alarms people.

Do you get twins from letrozole?

The chance of a multiple pregnancy exists but is lower than with clomiphene, often a few percent. Follicle monitoring by ultrasound helps show how many follicles are maturing before ovulation arrives.

Letrozole is a good example of a drug that became the standard in fertility care by way of an entirely different condition. Do not let the leaflet put you off, but do ask your doctor directly about the number of follicles on the scan before you sit out the wait. That one conversation says more about your cycle than any average from a study.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

• Farmacotherapeutisch Kompas. Letrozole. Accessed 2026.
• Thuisarts.nl. I have polycystic ovary syndrome (PCOS) and want to become pregnant. Accessed 2026.
• Legro RS, et al. Letrozole versus clomiphene for infertility in the polycystic ovary syndrome. New England Journal of Medicine, 2014. PMID 25006718.
• Franik S, et al. Aromatase inhibitors (letrozole) for ovulation induction in infertile women with polycystic ovary syndrome. Cochrane Database of Systematic Reviews, 2022. PMID 36165742.
• Roque M, et al. Letrozole versus clomiphene citrate in polycystic ovary syndrome: systematic review and meta-analysis. Gynecological Endocrinology, 2015. PMID 26479460.