What are the indications, dosing regimens, contraindications, and monitoring recommendations for Norgest (norethisterone)?

Norethisterone (Norgest): Clinical Overview

Norethisterone is a synthetic progestogen used primarily for endometrial protection in hormone replacement therapy, management of abnormal uterine bleeding, and as a component of combined oral contraceptives, with dosing ranging from 0.35 mg daily for contraception to 10-30 mg daily for acute bleeding control.

Primary Indications

Hormone Replacement Therapy (HRT)

Norethisterone serves as endometrial protection when combined with estrogen therapy 1:

• Sequential regimens: 10 mg daily for 12-14 days per month when combined with transdermal or oral 17β-estradiol
• Continuous regimens: Minimum 1 mg daily for continuous endometrial protection 1
• Position in therapy: Second-line choice after micronized progesterone (MP), which demonstrates superior cardiovascular and thrombotic safety profiles 1

The 2021 Blood Reviews guidelines specifically note that norethisterone acetate (NA) combined with ethinyl estradiol showed worse cardiovascular profiles (blood pressure, renal function, renin-angiotensin activation) compared to 17β-estradiol with micronized progesterone 1.

Abnormal Uterine Bleeding (AUB)

For acute severe bleeding: 10-30 mg daily until bleeding cessation, typically achieved within 46 hours (range 8-120 hours) 2. A 2025 randomized controlled trial demonstrated that 10 mg daily norethisterone acetate achieved bleeding cessation in 86.7% of patients within 7 days versus 48.9% with placebo 3.

For chronic management: 5 mg daily continuously effectively controls dysmenorrhea and reduces menstrual bleeding 4.

Contraception

As norgestimate (a norethisterone derivative) combined with ethinyl estradiol 5:

• Standard dosing: One active tablet daily for 21 days, followed by 7 days of inactive tablets
• Efficacy: Highly effective when taken consistently at intervals not exceeding 24 hours 5

Dosing Regimens by Indication

HRT Context

• Sequential: 10 mg daily × 12-14 days per month 1
• Continuous: 1 mg minimum daily 1
• Duration: Continue until average age of natural menopause (45-55 years) in premature ovarian insufficiency 1

AUB Management

• Acute severe bleeding: 10-30 mg daily (dose adjusted by severity, bleeding duration, patient weight) until 2 consecutive bleeding-free days or 30 days maximum 3, 2
• Chronic control: 5 mg daily continuously 4

Endometrial Protection

Doses as low as 0.1 mg daily combined with estradiol 1 mg effectively prevent endometrial hyperplasia (0.8% incidence versus 14.6% with unopposed estrogen) 6. Standard protective doses are 0.35 mg daily for continuous regimens 7.

Contraindications

Absolute Contraindications

• Personal history of arterial events (coronary disease, stroke) - estrogen-progestin combinations formally contraindicated 8
• Active or history of venous thromboembolism - particularly relevant given norethisterone's partial conversion to ethinyl estradiol 9
• Migraine with aura - due to stroke risk from ethinyl estradiol component 9
• Breast cancer (current or history) - moderately increased risk with long-term use 9
• Severe hepatic impairment - steroid hormones poorly metabolized 5
• Pregnancy 5

Relative Contraindications Requiring Careful Assessment

• Cardiovascular risk factors: LDL-cholesterol >2.20 g/L without other risk factors; lower thresholds apply with multiple risk factors 8
• Hypertriglyceridemia: Triglycerides >2.00 g/L contraindicate estrogen-progestin combinations 8
• Postpartum period <4 weeks: Increased thrombotic risk 5
• Smoking: Particularly concerning with estrogen-containing formulations 8

Critical Safety Considerations

Unique Pharmacological Property

Norethisterone converts to ethinyl estradiol: 10-20 mg norethisterone produces 20-30 μg ethinyl estradiol equivalents 9. This conversion carries important implications:

• Thrombotic risk: Dose-dependent; contraceptive doses carry no increased risk, but therapeutic doses (≥10 mg) may increase VTE risk 9
• Stroke risk: Theoretical concern in women with migraine with aura, though not specifically studied for therapeutic norethisterone use 9
• Cardiovascular effects: Negative impact on blood pressure, lipid profiles, and carbohydrate metabolism compared to micronized progesterone 1

Monitoring Recommendations

Baseline assessment:

• Blood pressure
• Lipid profile (particularly if cardiovascular risk factors present)
• Liver function tests
• Thrombophilia screening if strong family history of VTE before age 60 8

Ongoing monitoring:

• Blood pressure at each visit
• Lipid profiles periodically in at-risk patients 7
• Bone density (dual-energy x-ray absorptiometry) when used for HRT 7
• Clinical assessment for breakthrough bleeding patterns

Important caveat: FSH levels cannot monitor adequacy of hormone replacement, as inhibin also regulates FSH secretion 7.

Clinical Pearls and Pitfalls

Advantages

• Potent endometrial effects: Excellent for treating abnormal bleeding and providing endometrial protection 9
• Rapid bleeding control: Median cessation in 3 days for acute AUB 3
• Bone benefits: Positive effects on bone mineral density 9
• Cost-effective: Significantly less expensive than combined oral contraceptives for dysmenorrhea management 4

Disadvantages and Warnings

• Bleeding recurrence: Despite effective acute control, bleeding recurs quickly (median 5 days) after stopping treatment 3
• Anti-androgenic effects: Should be avoided in women with hypoandrogenism (e.g., cancer survivors with POI) as it may worsen libido and sexual function 1
• Metabolic effects: Less favorable cardiovascular profile than micronized progesterone 1
• Breast cancer risk: Slightly increased with long-term use 9

Practical Management

When prescribing for acute AUB, counsel patients that:

• Treatment may need repeating (up to 3 cycles over 210 days) 3
• Bleeding typically stops within 2-8 days 3, 2
• Side effects are generally minor; serious adverse events rare 2
• Backup contraception needed if used in reproductive-age women not seeking pregnancy

For HRT in premature ovarian insufficiency: Prioritize transdermal 17β-estradiol with micronized progesterone as first-line; reserve norethisterone as second-line when MP unavailable or not tolerated 1.