Recommended Dosage of Norethisterone for Contraception and Menstrual Disorders
For contraception, norethisterone is recommended at 0.35 mg daily as a progestin-only pill, while for menstrual disorders, the recommended dose ranges from 5 mg twice daily on days 19-26 of the menstrual cycle for cyclical regimens to 2.5-5 mg daily for continuous treatment. 1, 2
Dosage for Contraception
- Progestin-only oral contraceptives containing norethisterone are indicated for pregnancy prevention at a dose of 0.35 mg daily 1
- If used perfectly, the first-year failure rate for progestin-only oral contraceptives is 0.3%, though typical failure rates are closer to 9% due to missed or late pills 1
- Norethisterone must be taken at the same time each day to maintain contraceptive efficacy 3
Dosage for Menstrual Disorders
Cyclical/Sequential Regimen
- 5 mg twice daily on days 19-26 of the menstrual cycle is the standard sequential regimen for managing dysmenorrhea and menorrhagia 2, 4
- This regimen provides controlled withdrawal bleeding while offering symptom relief 2
- Studies show this regimen can significantly reduce menstrual blood loss from a median of 109 mL to 92 mL per cycle 4
Continuous Regimen
- Minimum effective dose of 1 mg daily when used continuously, particularly when withdrawal bleeding is not desired 3, 2
- Standard therapeutic dose of 2.5-5 mg daily is commonly prescribed for continuous symptom management 2, 5
- For severe symptoms, doses up to 5 mg three times daily (15 mg total) have been used for menstrual disorders 5, 6
- Continuous regimens require a minimum of 1 mg daily for endometrial protection 3, 2
Mechanism of Action and Efficacy
- For contraception: Norethisterone works primarily by thickening cervical mucus, inhibiting sperm penetration, and creating an unfavorable endometrial environment for implantation 1
- For menstrual disorders: Norethisterone reduces menstrual pain by thinning the endometrial lining, resulting in decreased prostaglandin production 2
- At higher doses (≥3 mg daily), norethisterone can inhibit ovulation, enhancing its contraceptive effect 7
- Studies show that 1.5 mg daily is insufficient for complete ovulation inhibition in most women 7
Important Considerations and Side Effects
- Progestins like norethisterone should not be used continuously for more than 6 months due to potential risk of meningioma 2
- Common side effects include changes in mood, breast tenderness, and irregular bleeding patterns 2
- Norethisterone may be preferred over combined hormonal contraceptives for patients with increased thrombotic risk 3
- In patients with hereditary angioedema, norethisterone at 10 mg daily has been used with good tolerance 3
- Breakthrough bleeding may occur, requiring dose adjustment; increasing the dose by 2.5 mg/day is recommended in such cases 5
Special Populations
- For patients with iatrogenic premature ovarian insufficiency requiring hormone therapy without contraception, continuous regimens require a minimum of 1 mg of oral norethisterone daily 3
- Progestational agents like norethisterone are preferred over combined oral contraceptives for menstrual suppression during thrombocytopenic periods 2
Clinical Pearls
- When used for contraception, norethisterone must be taken consistently at the same time each day to maintain efficacy 1
- For menstrual disorders, the dose and regimen should be selected based on whether cyclic bleeding is desired or not 2
- Higher doses provide better symptom control but may increase the risk of side effects 7