What is the recommended dose of norethisterone for oral contraception and for treating menstrual disorders such as irregularities, dysmenorrhea, delayed menses, endometriosis, or heavy menstrual bleeding?

Norethisterone Dosing Recommendations

For oral contraception, norethisterone is dosed at 0.35 mg daily taken continuously at the same time each day, while for treating menstrual disorders the dose varies: 5 mg three times daily (days 5-26 of cycle) for heavy menstrual bleeding, or a minimum of 1 mg daily for continuous hormone replacement therapy regimens. 1, 2

Oral Contraception

The FDA-approved dose for contraception is norethisterone 0.35 mg taken orally once daily without interruption 1. This progestin-only pill must be taken at the same time every day—timing is critical, as taking the pill more than 3 hours late requires backup contraception for the next 48 hours 1.

Key contraceptive considerations:

• Typical use failure rate: 9% (perfect use: 0.3%) 1
• Rapid return to fertility upon discontinuation 1
• Safe for postpubertal adolescents and breastfeeding women 1

Important Caveat for Adolescents

Recent evidence suggests that younger patients and those with obesity or heavy menstrual bleeding are less likely to achieve menstrual suppression with norethisterone 0.35 mg and may require higher doses of norethisterone acetate 3. This represents a critical gap between prescribing patterns and clinical outcomes.

Treatment of Menstrual Disorders

Heavy Menstrual Bleeding (Menorrhagia)

Norethisterone 5 mg three times daily from day 5 to day 26 of the menstrual cycle is the established regimen 2. This cyclical dosing achieved an 87% reduction in menstrual blood loss in controlled trials 4. However, patient satisfaction with this regimen is notably lower (22% continuation rate) compared to alternative treatments like the levonorgestrel IUD (76% continuation) 4.

Alternative dosing for continuous regimens: When used in hormone replacement therapy to avoid withdrawal bleeding, a minimum of 1 mg daily is required for endometrial protection 5.

Dysmenorrhea

For dysmenorrhea, combined formulations containing 1 mg norethisterone with 0.02-0.035 mg ethinyl estradiol have demonstrated efficacy 6, 7. The ultra-low-dose combination (0.02 mg ethinyl estradiol + 1 mg norethisterone) significantly reduced dysmenorrhea scores compared to placebo while maintaining a favorable safety profile 6.

Menstrual Irregularities and Delayed Menses

Historical data supports 2 mg norethisterone with 0.1 mg mestranol for managing irregular menses, though this specific formulation may not be widely available 7. For contemporary practice, the 5 mg three times daily cyclical regimen (days 5-26) remains the standard approach 2.

Endometriosis

While norethisterone can be used for endometriosis-associated pain, dienogest has emerged as superior for treating dyspareunia specifically 8. If norethisterone is chosen, continuous dosing at higher progestin levels would be required, though specific norethisterone dosing for endometriosis is not well-established in the provided evidence.

Hormone Replacement Therapy Context

In HRT regimens (particularly for premature ovarian insufficiency), norethisterone serves as a second-choice progestin after micronized progesterone 5:

• Sequential regimens: Not specifically dosed in guidelines (micronized progesterone or medroxyprogesterone acetate preferred)
• Continuous regimens: Minimum 1 mg daily for endometrial protection 5

Critical note: Norethisterone is considered inferior to micronized progesterone due to less favorable cardiovascular and metabolic profiles 5.

Practical Prescribing Algorithm

For contraception:

• Start 0.35 mg daily
• Counsel on strict timing requirements
• Consider higher doses (norethisterone acetate) in obese patients or those with heavy baseline bleeding 3

For heavy menstrual bleeding:

• First-line: 5 mg three times daily, days 5-26
• Expect 87% reduction in blood loss but lower satisfaction
• Consider levonorgestrel IUD as superior alternative 4

For dysmenorrhea:

• Use combined formulation (1 mg norethisterone + low-dose ethinyl estradiol)
• Ultra-low-dose options available for long-term use 6

For endometriosis:

• Consider dienogest instead for dyspareunia 8
• If norethisterone used, employ continuous dosing

Safety Considerations

Common side effects include menstrual irregularities (most frequent), headache, mood changes, and bloating 2, 1. Norethisterone may worsen hypoandrogenism in patients with low testosterone 5. Drug interactions are significant—particularly with enzyme inducers (rifampin, anticonvulsants) which reduce efficacy, and HIV/HCV protease inhibitors which have variable effects 1.