Is norethindrone (progestin) effective as a form of birth control?

Norethindrone as Birth Control: Effectiveness and Considerations

Norethindrone progestin-only pills are effective as birth control with a typical use failure rate of approximately 6% (perfect use 0.2%) when taken consistently at the same time every day. 1

Mechanism of Action

Norethindrone progestin-only pills (POPs) prevent pregnancy through multiple mechanisms:

• Suppressing ovulation in approximately half of users
• Thickening cervical mucus to inhibit sperm penetration
• Lowering mid-cycle LH and FSH peaks
• Slowing ovum movement through fallopian tubes
• Altering the endometrium 1

Effectiveness

• Perfect use: 0.2% failure rate
• Typical use: Approximately 6% failure rate 2
• In a 5-year study with 168 women using norethindrone 0.35 mg daily, the effectiveness rate was:
  • Drug-effectiveness rate: 1.9 per 100 woman-years
  • Use-effectiveness rate: 2.5 per 100 woman-years 3

Administration Requirements

For maximum effectiveness, norethindrone must be taken:

• At exactly the same time every day
• Continuously with no interruption between pill packs
• A backup method should be used for 48 hours if a pill is taken 3+ hours late 1

Safety Profile Advantages

Norethindrone POPs offer several safety advantages compared to combined hormonal contraceptives:

• No increased risk of venous thromboembolism (VTE) - relative risk of 0.90 (95% CI 0.57–1.45) compared to non-users 4
• No effect on blood pressure 4
• Safe for women with contraindications to estrogen 4
• Can be used by women with cardiovascular risk factors 4

Side Effects and Considerations

1. Menstrual Changes:

   • Irregular bleeding patterns in up to 25% of users
   • Breakthrough bleeding, spotting, or changes in cycle length 4

2. Metabolic Effects:

   • Minimal effect on lipid metabolism
   • HDL, HDL2, and apolipoprotein A-I and A-II may be decreased
   • No effect on total cholesterol, HDL3, LDL, or VLDL 1

3. Other Considerations:

   • Small amounts of progestin pass into breast milk (1-6% of maternal plasma levels)
   • Rare cases of decreased milk production have been reported 1
   • Rapid return to fertility after discontinuation 1

Drug Interactions

Effectiveness may be reduced when co-administered with:

• Rifampin
• Anticonvulsants (barbiturates, phenytoin, carbamazepine, felbamate, oxcarbazepine, topiramate)
• Griseofulvin
• St. John's Wort
• Certain anti-HIV protease inhibitors 1

Special Populations

1. Women with cardiovascular risk factors:

   • POPs are safer alternatives to combined hormonal contraceptives 4
   • Table 14 from the American Heart Association shows no increased stroke risk with progestin-only methods 2

2. Adolescents:

   • Safety and efficacy are the same for postpubertal adolescents as for adult women
   • Not indicated before menarche 1

Practical Considerations

• Patient education about expected side effects before starting can improve adherence
• Regular follow-up visits 1-3 months after initiation are recommended
• Blood pressure monitoring is advised but less critical than with combined hormonal contraceptives 4

Pitfalls to Avoid

1. Timing errors: Taking pills more than 3 hours late significantly reduces effectiveness
2. Drug interactions: Certain medications can reduce effectiveness
3. Inadequate counseling: Patients should be informed about irregular bleeding patterns to improve adherence
4. Failure to use backup method: When pills are taken late or with interacting medications

Norethindrone POPs provide an effective contraceptive option with a favorable safety profile, particularly for women with contraindications to estrogen-containing contraceptives. The key to effectiveness is consistent daily administration at the same time.