Norethisterone, a first-generation progestin, exerts its effects through:

1. Endometrial Transformation: Converts proliferative endometrium into secretory tissue, stabilizing the lining and preventing irregular bleeding (Lippincott).
2. Pituitary Suppression: Inhibits the release of gonadotropins (FSH and LH), preventing ovulation at higher doses (Lange).
3. Anti-Estrogenic Effects: Counteracts estrogen-induced endometrial hyperplasia, reducing the risk of abnormal growth.

Norethisterone also has mild androgenic and glucocorticoid activity, which may contribute to some side effects.

1. Menstrual Disorders:
   • Dysfunctional Uterine Bleeding (DUB): Controls heavy or irregular bleeding.
   • Amenorrhea: Induces withdrawal bleeding in secondary amenorrhea.
2. Endometriosis: Reduces pain and inflammation by suppressing endometrial tissue growth (BNF).
3. Premenstrual Syndrome (PMS): Alleviates physical and emotional symptoms.
4. Contraception: Used in combination with estrogen for hormonal contraception.
5. Hormone Replacement Therapy (HRT): Combined with estrogen to prevent endometrial hyperplasia in postmenopausal women (Lippincott).

• Dysfunctional Uterine Bleeding: 5 mg twice daily for 10 days to stop bleeding, followed by 5 mg daily from day 19 to 26 of the cycle to regulate menstruation (BNF).
• Endometriosis: 5 mg three times daily for 6–9 months.
• Amenorrhea: 5 mg twice daily for 5–7 days to induce withdrawal bleeding.
• PMS: 5 mg twice daily from day 19 to 26 of the cycle.

• Common: Nausea, headache, breast tenderness, weight gain, and mood changes.
• Serious:
  • Thromboembolism: Rare but possible, particularly in high-risk patients (Lange).
  • Hepatic Effects: Rare hepatotoxicity or benign liver tumors.
  • Androgenic Effects: Acne, hirsutism, or hair loss due to mild androgenic activity (Lippincott).

• Absolute Contraindications: History of thromboembolic disorders, severe liver disease, or undiagnosed vaginal bleeding (BNF).
• Relative Precautions: Diabetes, hypertension, or history of depression.
• Monitoring: Regular blood pressure checks and liver function tests in long-term users.

• Reduced Efficacy: Enzyme-inducing drugs (e.g., rifampicin, carbamazepine, St. John’s Wort) accelerate metabolism of norethisterone, reducing its effectiveness (BNF).
• Anticoagulants: May reduce the efficacy of warfarin; monitor INR closely.
• Other Hormonal Therapies: Avoid concurrent use with other progestins or estrogens unless prescribed as part of HRT (Lippincott).

• Active Ingredient: Norethisterone (5 mg).

Brands: Marketed as Primolut-N; generics may be labeled as norethisterone.