What are the side effects of Micronor (norethindrone), a progestin-only birth control pill?

Side Effects of Micronor (Norethindrone)

Menstrual irregularity is the most common side effect of Micronor (norethindrone), with frequent and irregular bleeding being particularly prevalent, while amenorrhea is less common. 1

Common Side Effects

• Menstrual disturbances: The most frequently reported side effect, affecting up to 25% of users and being the most common reason for discontinuation 1, 2

  • Increased frequency of bleeding episodes 2
  • Breakthrough bleeding and spotting 2
  • Prolonged bleeding 1
  • Irregular cycles 2
  • Amenorrhea (less common than other bleeding patterns) 1

• Other common side effects:

  • Headache 1
  • Breast tenderness 1
  • Nausea 1
  • Dizziness 1

Less Common Side Effects

• Androgenic effects (rare):
  • Acne 1, 3
  • Hirsutism (excessive hair growth) 1, 3
  • Weight gain 1, 3

Management of Side Effects

Managing Menstrual Irregularities

• If unscheduled spotting or bleeding persists and is unacceptable to the patient, consider alternative contraceptive methods 4
• Enhanced counseling about expected bleeding patterns and reassurance that these irregularities are generally not harmful can reduce method discontinuation 4
• For persistent problematic bleeding, adding 5 mg norethisterone acetate has been shown to significantly reduce bleeding frequency and quantity in women using progestin-only pills 5

Counseling Points

• Emphasize the importance of correct and consistent pill use to minimize bleeding irregularities 4
• Inform patients that menstrual disturbances typically improve over time with continued use 4
• Advise that progestin-only pills work primarily by thickening cervical mucus and may not always inhibit ovulation 4

Effectiveness and Considerations

• Approximately 9 out of 100 women become pregnant in the first year of use with typical use of progestin-only pills 4
• Progestin-only pills do not protect against sexually transmitted diseases; consistent and correct use of condoms is recommended for STD protection 4
• Progestin-only pills are reversible and can be used by women of all ages 4

Special Considerations

• Progestin-only pills may interfere with the contraceptive effect of microdosed progestin minipills 4
• Patients should be monitored for changes in health status during therapy 6
• Annual clinical review is recommended for stable patients, with more frequent monitoring during initial therapy 6

Contraindications

• Pregnancy (Category X) 6
• History of breast cancer 6

The progestin-only pill remains an underutilized but effective second-line contraceptive option, particularly valuable for women who cannot use estrogen-containing contraceptives 7. Despite its reasonable efficacy, the menstrual disturbances remain the primary barrier to wider acceptance and continued use 2.