How should norethisterone 5 mg be prescribed (dose, timing, duration, contraindications, side‑effects) for a non‑pregnant, non‑breastfeeding woman of reproductive age with delayed or light heavy menstrual bleeding?

Norethisterone 5mg BD for Heavy Menstrual Bleeding

Norethisterone 5mg twice daily for 5 days is an inadequate regimen for managing heavy menstrual bleeding and should not be used; instead, prescribe norethisterone 5mg three times daily (15mg total daily) from day 5 to day 26 of the cycle for at least 3 months to achieve meaningful reduction in menstrual blood loss. 1, 2, 3

Correct Dosing Regimen

The evidence-based approach for norethisterone in heavy menstrual bleeding requires:

• Dose: 5mg three times daily (total 15mg/day) 1, 2, 3
• Timing: Day 5 to day 26 of the menstrual cycle (for ovulatory bleeding) 2, 3
• Duration: Minimum 3 cycles (3 months) to assess therapeutic response 3

Why the 5mg BD for 5 Days Regimen Fails

The proposed regimen of 5mg twice daily for only 5 days is fundamentally flawed because:

• Insufficient daily dose: 10mg/day is inadequate compared to the evidence-based 15mg/day needed for menstrual blood loss reduction 1, 2
• Too short duration: 5 days provides inadequate endometrial suppression, whereas 21-22 days per cycle (day 5-26) is required for ovulatory dysfunctional bleeding 2, 3
• Wrong indication: This brief regimen resembles menstrual delay dosing (which uses 5mg TID for 3-14 days before expected menses), not treatment for heavy bleeding 4

Evidence-Based Prescribing Algorithm

For Ovulatory Heavy Menstrual Bleeding:

• Norethisterone 5mg three times daily from day 5 to day 26 of each cycle 2, 3
• Reduces median menstrual blood loss by 87% (from 109mL to 92mL) 1
• Comparable efficacy to mefenamic acid but with different mechanism 1

For Anovulatory Bleeding:

• Norethisterone 5mg three times daily from day 12 to day 25 of each cycle 2
• Reduces menstrual blood loss from median 131mL to 64-80mL 2

Expected Outcomes and Monitoring

Therapeutic response timeline:

• Significant reduction in blood loss typically seen after first treatment cycle 1, 2
• Duration of bleeding decreases (median 7 days to 5 days) 1
• Full assessment requires 3 months of treatment 3

Success rates:

• 48% of women achieve normal menstrual blood loss (<80mL) after 2 months 1
• 67% may remain menorrhagic despite treatment, requiring alternative therapy 1

Contraindications

Absolute contraindications:

• Current or history of venous thromboembolism 4
• Active liver disease or hepatic tumors 4
• Undiagnosed vaginal bleeding 4
• Pregnancy 4
• Breast cancer or hormone-sensitive malignancies 4

Relative cautions:

• History of depression 4
• Cardiovascular risk factors 4
• Migraine with aura if over age 35 4

Common Side Effects

• Weight gain (approximately 2kg in 28% of users) 5
• Intracyclic bleeding/spotting (1.2-2.4% of cycles) 5
• Amenorrhea (2.5% of cycles) 5
• Low continuation rate: only 22% wish to continue after 3 cycles due to daily dosing burden 3

Critical Clinical Pitfalls to Avoid

Inadequate treatment duration: Prescribing for only 5 days will not provide endometrial protection or meaningful blood loss reduction 2, 3

Wrong daily dose: Using 10mg/day instead of 15mg/day reduces efficacy significantly 1, 2

Not assessing ovulatory status: Anovulatory bleeding requires different timing (day 12-25) versus ovulatory bleeding (day 5-26) 2

Premature discontinuation: Stopping before 3 months prevents adequate assessment of therapeutic response 3

Failure to consider superior alternatives: The levonorgestrel intrauterine system reduces menstrual blood loss by 94% with 76% continuation rate versus 22% for norethisterone, making it a more effective first-line option 3

When Norethisterone Fails

If bleeding persists after 3 months of appropriate norethisterone therapy:

• Consider NSAIDs for short-term treatment (5-7 days during bleeding) 6
• Evaluate for underlying pathology (fibroids, polyps, adenomyosis) 6
• Offer alternative contraceptive methods, particularly levonorgestrel IUD 3
• Consider combined hormonal contraceptives if medically eligible 6