Bottom Line Up Front
ASRM now recommends letrozole (Femara) as first-line for ovulation induction in PCOS, replacing clomid's decades-long reign. Letrozole shows higher live birth rates (27.5% vs 19.1% in the landmark PPCOS II trial), fewer multiples, and a more favorable endometrial effect. Both are affordable oral medications taken for 5 days early in the cycle.
How They Work: Different Mechanisms, Same Goal
Letrozole is an aromatase inhibitor — it temporarily blocks the conversion of androgens to estrogen, causing the brain to sense low estrogen and release more FSH. This stimulates follicle growth. Because the effect is temporary and the drug clears quickly, it doesn't thin the endometrial lining the way clomid can.
Clomid (clomiphene citrate) is a selective estrogen receptor modulator (SERM) — it blocks estrogen receptors in the hypothalamus, similarly tricking the brain into producing more FSH. However, it also blocks estrogen receptors in the uterine lining and cervix, which can thin the endometrium and reduce cervical mucus — both potentially counterproductive.
Head-to-Head Comparison
| Factor | Letrozole (Femara) | Clomid (Clomiphene) |
|---|---|---|
| Ovulation rate (PCOS) | 61.7% | 48.3% |
| Live birth rate (PPCOS II) | 27.5% | 19.1% |
| Multiple pregnancy rate | 3.4% | 7.4% |
| Endometrial effect | Neutral to positive | Can thin the lining |
| Cervical mucus effect | Neutral | Can reduce and thicken |
| Typical dose range | 2.5–7.5mg × 5 days | 50–150mg × 5 days |
| Approximate cost | $10–$50/cycle (generic) | $10–$50/cycle (generic) |
| FDA fertility approval | Off-label (approved for breast cancer) | FDA-approved for ovulation induction |
The "Off-Label" Question
Letrozole is technically used off-label for fertility — it's FDA-approved for breast cancer. This does not mean it's experimental or unsafe. Off-label use is standard practice in medicine when clinical evidence supports it, and the evidence for letrozole in fertility is robust. ASRM's endorsement reflects this.
When Clomid Still Makes Sense
Despite letrozole's advantages, clomid isn't obsolete. Some patients respond better to clomid, and it remains a reasonable option for unexplained infertility (where the evidence advantage for letrozole is less clear than for PCOS), patients who don't respond to letrozole, and situations where a physician is more experienced with clomid protocols.
Moving Beyond Oral Medications
If 3–6 cycles of oral ovulation induction (with either medication) don't result in pregnancy, the next step is typically injectable gonadotropins (FSH injections) with IUI, or progression to IVF. Don't stay on oral medications indefinitely — there's limited benefit beyond 6 cycles, and the time spent may come at the cost of declining ovarian reserve.
When Medication Alone Isn't Enough
If ovulation induction hasn't worked, IVF is often the next step. International options can make this transition more affordable.
Explore IVF Options →