Microlut prevents pregnancy through three primary mechanisms:

1. Cervical Mucus Alteration: Thickens cervical mucus, creating a barrier to sperm penetration (Lippincott).
2. Endometrial Changes: Thins the endometrial lining, reducing the likelihood of implantation.
3. Ovulation Suppression: In some women, levonorgestrel inhibits the release of luteinizing hormone (LH), preventing ovulation (Lange).

Levonorgestrel, a second-generation progestin, has high progestogenic activity with minimal androgenic effects, making it well-tolerated.

1. Contraception: Primary indication, with >99% efficacy when used correctly (BNF).
2. Estrogen Contraindications: Suitable for women with contraindications to estrogen, such as a history of venous thromboembolism (VTE), hypertension, or migraine with aura.
3. Breastfeeding: Safe for use during lactation, as it does not affect milk supply (Lippincott).

• Standard Regimen: One tablet (30 µg levonorgestrel) daily at the same time each day, without a hormone-free interval (BNF).
• Initiation: Start on day 1 of menstruation for immediate protection. If started later, use backup contraception for 7 days.
• Missed Dose: If delayed >3 hours, take the missed pill immediately and use backup contraception for 7 days.

• Common: Irregular menstrual bleeding (e.g., spotting, amenorrhea), headache, breast tenderness, nausea, and mood changes.
• Serious:
  • Ectopic Pregnancy: Rare but possible due to altered tubal motility (Lange).
  • Ovarian Cysts: Benign functional cysts may occur due to suppressed ovulation.
  • Hepatic Effects: Rare hepatotoxicity or benign liver tumors (BNF).

• Absolute Contraindications: History of progesterone-dependent tumors, severe liver disease, or undiagnosed vaginal bleeding (BNF).
• Relative Precautions: History of depression, diabetes, or risk factors for ectopic pregnancy.
• Monitoring: Regular follow-up for menstrual irregularities and screening for hepatic dysfunction in long-term users.

• Reduced Efficacy: Enzyme-inducing drugs (e.g., rifampicin, carbamazepine, St. John’s Wort) accelerate metabolism of levonorgestrel, necessitating alternative contraception (BNF).
• Antibiotics: Limited evidence for interaction with broad-spectrum antibiotics (e.g., amoxicillin), but backup contraception is advised.
• Other Interactions: Avoid concurrent use with hepatotoxic drugs (e.g., acetaminophen overdose) or cyclosporine (levonorgestrel may increase plasma levels) (Lippincott).

• Active Ingredient: Levonorgestrel (30 µg).
• Brands: Marketed as Microlut; generics may be labeled as levonorgestrel.