Mirena (Levonorgestrel)

Levonorgestrel delivered via Mirena acts on the reproductive hormonal axis to provide contraception and control uterine bleeding.

• Contraception: Provides highly effective, long‑term birth control for up to five years.
• Heavy menstrual bleeding: Reduces menstrual blood loss and improves anemia associated with menorrhagia.
• Endometrial hyperplasia (non‑cancerous): Suppresses proliferation of the endometrial lining in selected cases.
• Estrogen therapy adjunct: Provides endometrial protection for women using systemic estrogen.

• Mirena releases levonorgestrel directly into the uterine cavity at a low, steady rate. The hormone binds to progesterone receptors in the cervical mucus, endometrium and hypothalamic‑pituitary axis, causing thickening of cervical mucus, inhibition of endometrial proliferation, and, in many users, suppression of ovulation, thereby preventing implantation and reducing menstrual bleeding.

Levonorgestrel delivered by the Mirena intrauterine system may be associated with a range of adverse reactions.

Common Side Effects

• Irregular bleeding or spotting: Unpredictable menstrual patterns, especially during the first months.
• Amenorrhea: Absence of menstrual bleeding.
• Headache: Mild to moderate intensity.
• Breast tenderness: Discomfort or swelling of breast tissue.
• Acne or skin changes: New or worsening acne.
• Ovarian cysts: Small, functional cysts that often resolve spontaneously.

Serious or Rare Side Effects

• Pelvic inflammatory disease: Infection of the reproductive organs.
• Uterine perforation: Rare injury to the uterine wall during insertion.
• Expulsion of the device: Partial or complete loss of the IUS.
• Ectopic pregnancy: Pregnancy occurring outside the uterus if contraception fails.
• Severe allergic reaction: Rash, swelling, or anaphylaxis.
• Hormone‑related thromboembolic events: Blood clots in veins or arteries.

Before using Mirena, several safety considerations should be reviewed.

• Contraindications: Do not use in women with active pelvic infection, unexplained vaginal bleeding, or known or suspected pregnancy.
• Screening: Perform a pregnancy test and assess uterine cavity size before insertion.
• Follow‑up: Schedule a check‑up 4–6 weeks after placement to confirm correct positioning.
• Hormone sensitivity: Avoid in patients with known hypersensitivity to levonorgestrel or any IUS components.
• Breast cancer history: Use with caution in women with current or past estrogen‑dependent breast cancer.
• Store at ambient temperature: Keep the device in its original packaging, protect from moisture and extreme heat, and store below 25 °C.

Levonorgestrel released from Mirena can interact with other medicines that affect hormone metabolism or uterine environment.

Major Interactions (Avoid)

• Antiepileptic enzymes: Strong CYP3A4 inducers such as carbamazepine, phenytoin, or rifampicin may reduce levonorgestrel efficacy.
• Antiretrovirals: Certain protease inhibitors and efavirenz can lower hormone levels, increasing risk of unintended pregnancy.

Moderate Interactions (Monitor Closely)

• Antifungals: Ketoconazole and other azole antifungals may increase levonorgestrel concentrations.
• Antibiotics: While most do not affect IUS, prolonged use of rifampin‑based regimens warrants monitoring.
• Herbal supplements: St. John’s wort may decrease hormone effectiveness.
• Hormonal therapies: Concurrent use of other progestins or estrogen may alter bleeding patterns.