Will taking 100mg of micronized progesterone from day 5 to 28 of the menstrual cycle suppress ovulation?

Micronized Progesterone and Ovulation Suppression

Taking 100mg of micronized progesterone from day 5-28 of the menstrual cycle is unlikely to reliably suppress ovulation and should not be considered an effective contraceptive method.

Mechanism of Action and Dosing Considerations

Micronized progesterone at 100mg daily is significantly below the dosage typically required for ovulation suppression. According to CDC guidelines, seven consecutive days of hormonal contraceptive use is necessary to reliably prevent ovulation 1. The 100mg dose is particularly inadequate for this purpose when:

• Started on day 5 of the menstrual cycle (early follicular phase)
• Used as a standalone hormonal agent
• Compared to progestin formulations specifically designed for contraception

Dosage Context

• 100mg is half the typical dose (200mg) used in hormone replacement therapy 1
• Clinical studies typically use 200-300mg daily for endometrial protection 2
• Even at higher doses, micronized progesterone is not FDA-approved for contraception

Evidence on Progesterone and Ovulation

Research demonstrates that progesterone plays a critical role in the regulation of the midcycle gonadotropin surge that leads to ovulation 3. However:

• Natural progesterone at 100mg daily is insufficient to consistently block the hypothalamic-pituitary signals necessary for ovulation
• Studies show that progesterone's effect on ovulation is dose-dependent 4
• Bioavailability of oral micronized progesterone is variable between individuals 4

Route of Administration Considerations

The oral route for micronized progesterone has significant limitations:

• Lower bioavailability compared to vaginal or rectal administration 4, 5
• First-pass hepatic metabolism reduces systemic levels
• Significant interindividual variability in absorption and metabolism 2

Clinical Implications

For a patient considering this regimen:

1. Contraceptive efficacy: The proposed regimen would likely have minimal contraceptive effect
2. Endometrial effects: While 100mg may have some effect on the endometrium 6, this is insufficient for contraception
3. Timing issues: Starting on day 5 is too late to prevent follicular development that has already begun

Alternative Approaches

If contraception is the goal, more reliable options include:

• Combined hormonal contraceptives (pills, patch, ring)
• Progestin-only pills specifically formulated for contraception
• Long-acting reversible contraceptives (IUDs, implants)
• Injectable contraceptives (DMPA)

Conclusion

The proposed regimen of 100mg micronized progesterone from days 5-28 would not reliably suppress ovulation and should not be used for contraceptive purposes. The dose is insufficient, the timing is suboptimal, and the oral route has variable bioavailability.