How each cycle works, and what the evidence really says
By Dr. Neha Yadav, Infertility Specialist and IVF Expert, Salt Lake, Kolkata
When you are trying to conceive, irregular periods or difficulty ovulating can make the journey confusing. Your fertility specialist may recommend an ovulation-induction tablet such as letrozole or clomiphene to help an egg mature and release.
But which tablet is better?
The answer depends on the reason for your fertility difficulties. In women with polycystic ovary syndrome (PCOS) and irregular ovulation, letrozole is generally preferred as the first-line option. For unexplained infertility treated with intrauterine insemination (IUI), the evidence does not show that letrozole is always better than clomiphene.
Understanding the difference can help you have a more informed discussion with your fertility specialist.
Key Takeaways
Letrozole is the preferred first-line ovulation-induction tablet for many women with PCOS and irregular ovulation.
In a major PCOS trial, the live-birth rate was 27.5% with letrozole and 19.1% with clomiphene.
In unexplained infertility treated with IUI, clomiphene performed as well as or better than letrozole in the figures reported by the source material.
Both medicines can have side effects and may increase the possibility of multiple pregnancy.
Ultrasound monitoring and an individual treatment plan are important. Never take either medicine without medical guidance.
How Do Letrozole and Clomiphene Work?
Both medicines are used to encourage ovulation, but they work differently.
Letrozole
Letrozole briefly reduces oestrogen production. In response, the brain increases the hormonal signals that stimulate follicle development, including follicle-stimulating hormone (FSH).
It is commonly preferred for ovulation induction in women with PCOS who are not ovulating regularly.
If you have PCOS and irregular periods, you may also find our guide on irregular periods and their possible effects on fertility useful.
Clomiphene
Clomiphene works by blocking oestrogen receptors in the brain. This encourages the hormonal signals involved in follicle development and ovulation.
It remains an option in selected fertility-treatment plans. The best choice depends on the diagnosis and the type of treatment being considered.
Letrozole vs Clomiphene: A Comparison
The following figures are reported in the source document. They describe study outcomes, not an individual's guaranteed chance of pregnancy.
| Comparison | Letrozole | Clomiphene |
|---|---|---|
| Live birth in the cited PCOS trial | 27.5% | 19.1% |
| Ovulation per cycle in PCOS | 61.7% | 48.3% |
| Twin pregnancy in the cited PCOS trial | 3.4% | 7.4% |
| Live birth per cycle in unexplained infertility | 18.7% | 23.3% |
| Side effects highlighted in the source | More dizziness and fatigue; fewer hot flushes | More hot flushes |
The reported difference in twin rates was not statistically significant. The source also notes that a 2023 meta-analysis of 29 trials found live-birth rates of 33% with letrozole compared with 22% with clomiphene in PCOS.
These results support letrozole's role in PCOS-related ovulation problems. However, they do not mean that letrozole is the better choice for every fertility diagnosis.
Which Tablet Is Better for PCOS?
For women with PCOS who have irregular or absent ovulation and no other identified infertility factor, letrozole is generally the preferred first-line tablet according to the guidance cited in the source material.
PCOS can affect hormonal balance and the regular release of eggs. Ovulation-induction treatment aims to help a follicle mature and release an egg.
The choice and dose of medicine depend on your clinical history, previous treatment response and monitoring results.
Read more about trying to conceive naturally with PCOS to understand other aspects of fertility planning.
What About Unexplained Infertility?
Unexplained infertility is diagnosed when standard fertility investigations do not identify a clear cause, despite pregnancy not occurring.
In this situation, the evidence is different from that for PCOS. The figures reported in the source document show a live-birth rate per cycle of 18.7% with letrozole and 23.3% with clomiphene.
Therefore, the fact that letrozole is preferred for many women with PCOS does not automatically make it superior in unexplained infertility.
Treatment decisions should account for age, duration of infertility, previous treatment and whether IUI is appropriate.
For a broader overview, read our guide to unexplained infertility and the next steps when tests are normal.
What Happens During an Ovulation-Induction Cycle?
The exact schedule varies according to your treatment plan. A typical monitored cycle may follow these steps:
Early in the cycle: The doctor prescribes the selected tablet for a specified number of days, often beginning between cycle days 2 and 5.
Follicle monitoring: An ultrasound, often around days 10–14, assesses follicle development and the uterine lining. The timing depends on your response.
Ovulation timing: Your doctor advises when to have intercourse or undergo IUI. A trigger injection may sometimes be used.
Follow-up: The doctor may recommend progesterone testing or a pregnancy test at the appropriate time.
Review: If pregnancy does not occur after several ovulatory cycles, your doctor may reassess the dose, diagnosis or treatment approach.
Not everyone ovulates during the first treatment cycle. Some patients need a dose adjustment or a different plan.
If IUI is part of your treatment, read our step-by-step guide to the IUI process.
Do Letrozole and Clomiphene Have Side Effects?
Yes. Both medicines can cause side effects, and individual experiences vary.
According to the source document:
Letrozole was associated with more dizziness and fatigue in the cited comparison.
Clomiphene was associated with more hot flushes.
Both medicines require appropriate clinical supervision.
Multiple pregnancy, including twins, is a potential risk during ovulation-induction treatment.
Your doctor should explain the expected benefits, potential risks and monitoring schedule before treatment begins.
Myth vs Fact
Myth 1: Letrozole is a cancer medicine, so it cannot be used for fertility treatment.
Fact: Letrozole was originally developed for other medical uses, and its use for ovulation induction is off-label. The source document describes evidence supporting its use in PCOS, while noting that further research on some outcomes is needed. Your fertility specialist can explain whether it is appropriate for you.
Myth 2: The newest or most popular tablet is always better.
Fact: Treatment depends on the diagnosis. Letrozole is generally preferred for PCOS-related ovulation problems, but clomiphene remains a reasonable option in selected cases of unexplained infertility.
Myth 3: Ovulation tablets do not require monitoring.
Fact: Monitoring may be needed to assess follicle development and help manage the risks associated with treatment, including multiple pregnancy.
Myth 4: If the first cycle does not work, the treatment has failed.
Fact: Ovulation and pregnancy do not occur in every cycle. Your doctor may review the response, adjust the plan or discuss other options depending on your individual circumstances.
Which Ovulation Tablet Is Right for You?
Your fertility specialist may consider the following factors:
PCOS with irregular ovulation: Letrozole is generally preferred when there are no other factors changing the treatment plan.
Unexplained infertility: Letrozole or clomiphene may be considered, depending on the treatment approach and your clinical history.
Older age or tubal factors: Tablets alone may not address the underlying issue.
Male-factor infertility: Your partner's assessment, including semen analysis, may affect which treatment is appropriate.
Previous unsuccessful cycles: Your doctor may recommend reviewing the diagnosis, treatment response and next steps.
There is no single tablet or treatment schedule that is right for everyone.
Checklist Before Starting Treatment
Before taking letrozole or clomiphene, discuss the following with your doctor:
Have the relevant baseline assessment and hormone tests been completed?
Have your fallopian tubes been assessed for patency when appropriate?
Has your partner had a semen analysis?
When should you take the medicine, and what dose has been prescribed?
When should you attend for ultrasound monitoring?
What side effects or symptoms should you report?
When will your treatment plan be reviewed if pregnancy does not occur?
Never self-medicate with ovulation-induction tablets. Do not copy another person's dose or cycle schedule.
Frequently Asked Questions
Is letrozole better than clomiphene?
For many women with PCOS-related irregular ovulation, the evidence favours letrozole. For unexplained infertility, the best choice depends on the treatment plan and individual circumstances.
When should I take the tablet?
The source document describes a common schedule of one tablet daily for five days early in the cycle, often beginning between days 2 and 5. Your doctor must determine the exact starting day and dose.
Will I ovulate during my first cycle?
Not necessarily. The source reports ovulation in 61.7% of letrozole cycles and 48.3% of clomiphene cycles in the cited PCOS comparison. Individual responses vary.
Can these tablets cause twins?
Yes, multiple pregnancy is possible. In the cited PCOS comparison, twin rates were 3.4% with letrozole and 7.4% with clomiphene; the difference was not statistically significant.
How many cycles can I try?
The source notes that trials allowed up to four or five cycles in different study populations and that clinicians commonly reassess after several ovulatory cycles. Your doctor should set the review point according to your age, diagnosis and response to treatment.
Is letrozole safe for pregnancy?
The source document reports no statistically significant difference in birth defects between the two treatments in the cited PCOS trial, but it also notes that more research was requested. Discuss the benefits, risks and timing of treatment with your fertility specialist.
Get Personalised Fertility Guidance
Choosing between letrozole and clomiphene involves more than comparing success rates. Your diagnosis, ovulation pattern, age, fertility investigations and treatment goals all matter.
If you are experiencing irregular periods, PCOS or difficulty conceiving, consult a fertility specialist for an individual assessment.
Learn more about Dr. Neha Yadav, Infertility Specialist and IVF Expert in Salt Lake, Kolkata, or visit the Renew Healthcare website to explore fertility services.
This article is for general educational purposes and does not replace individual medical advice. Fertility treatment and medication should be prescribed and monitored by a qualified clinician.