What medications are used to induce ovulation?

Medications to Induce Ovulation

Clomiphene citrate is the first-line medication for ovulation induction, achieving approximately 80% ovulation rates and 50% pregnancy rates in women with polycystic ovary syndrome (PCOS). 1

First-Line Treatment: Clomiphene Citrate

Clomiphene citrate stands as the gold standard initial pharmacological intervention based on ACOG guidelines, supported by good and consistent scientific evidence 1. This selective estrogen receptor modulator works by blocking estrogen receptors, leading to increased gonadotropin release. When used in women with PCOS, approximately 80% will ovulate and half of those will conceive 1.

Important caveat: Clomiphene has antiestrogenic effects that can negatively impact cervical mucus and endometrial thickness, potentially limiting fertility despite successful ovulation 2.

Second-Line Treatment: Gonadotropins

When clomiphene fails, low-dose gonadotropin therapy (≤75 IU per day) is recommended over high-dose protocols 3, 1. Low-dose FSH protocols induce monofollicular development with significantly lower risk of ovarian hyperstimulation syndrome 1. The ACOG specifically recommends this approach based on its superior safety profile, though the evidence is limited or inconsistent 1.

For unexplained or mild male infertility with total motile sperm count >10 million, the guideline algorithm specifies using tamoxifen, clomiphene citrate, or ≤75 IU gonadotropins per day for ovarian stimulation 3.

Alternative Agents

Letrozole (Aromatase Inhibitor)

Letrozole represents a promising alternative that avoids the antiestrogenic effects of clomiphene 2. As an aromatase inhibitor, it blocks estrogen synthesis without depleting estrogen receptors, preserving normal cervical mucus and endometrial development. Research suggests it may be particularly effective in clomiphene-resistant cases 4, 2. However, this remains off-label use as the FDA has not approved letrozole for ovulation induction 2.

Insulin-Sensitizing Agents

Metformin and thiazolidinediones improve ovulation frequency in women with PCOS but are not FDA-approved for this indication 1. ACOG notes these interventions are beneficial for improving ovulation frequency based on good and consistent evidence, but their effects on early pregnancy outcomes remain uncertain 1. Metformin appears safer than thiazolidinediones in this context 1.

Treatment Algorithm by Clinical Scenario

For PCOS Patients:

1. Start with lifestyle modification: Weight loss of just 5% improves metabolic and reproductive outcomes 1
2. First medication: Clomiphene citrate
3. If clomiphene fails: Low-dose FSH (≤75 IU/day)
4. Consider: Letrozole as alternative to clomiphene (off-label)
5. Adjunct therapy: Metformin for insulin resistance (off-label for ovulation)

For Unexplained Infertility with Good Prognosis (Hunault score >30%):

• Expectant management for 6-12 months first 3
• If unsuccessful, proceed to IUI with ovarian stimulation using clomiphene, tamoxifen, or low-dose gonadotropins 3

For Hypogonadotropic Hypogonadism:

• Requires both FSH and LH administration 4
• Alternative: Pulsatile GnRH has equivalent effectiveness with lower multiple pregnancy rates 4
• Pregnancy rates approach 25% per cycle in this well-defined population 5

Critical Safety Considerations

Cancel cycles or convert to IVF when >2 follicles reach >15mm OR when 1-2 follicles are >15mm AND ≥5 follicles are >10mm 3. This prevents high-order multiple pregnancies and severe ovarian hyperstimulation syndrome.

Do not use GnRH agonists or antagonists for routine ovulation induction 3. These are reserved for controlled ovarian hyperstimulation in IVF protocols.

Monitoring and Timing

Trigger ovulation with hCG when 1-2 follicles reach >15mm with <5 follicles >10mm 3. Perform insemination 24-40 hours after hCG or one day after detecting spontaneous LH surge 3.

Common Pitfall

The most significant error is using high-dose gonadotropin protocols, which dramatically increase risks of multiple pregnancy and ovarian hyperstimulation without improving monofollicular ovulation rates 1. Always start with the lowest effective dose.