Mirena (Levonorgestrel)

Mirena, a levonorgestrel‑releasing intrauterine system, is used in gynecologic care to provide hormonal contraception and manage menstrual disorders.

• Contraception: provides up to five years of highly effective reversible birth control.
• Heavy menstrual bleeding (menorrhagia): reduces menstrual blood loss and may improve anemia.
• Endometrial protection in estrogen therapy: supplies progestogenic effect to prevent endometrial hyperplasia during combined hormone regimens.

• The intrauterine system continuously releases levonorgestrel, a synthetic progestin, which binds to progesterone receptors in the endometrium and cervical mucus. This action thickens cervical mucus to impede sperm passage, suppresses endometrial proliferation to reduce bleeding, and may inhibit ovulation in some users, collectively delivering reliable contraception and menstrual flow control.

Common Side Effects

• Irregular bleeding or spotting, especially during the first months.
• Amenorrhea (absence of periods) after prolonged use.
• Pelvic or uterine cramping after insertion.
• Breast tenderness or mild breast enlargement.
• Headache or mild nausea.
• Mood changes or acne.

Serious or Rare Side Effects

• Uterine perforation during insertion.
• Expulsion of the device requiring medical attention.
• Pelvic inflammatory infection within the first weeks.
• Development of ovarian cysts.
• Ectopic pregnancy if contraception fails.
• Severe abdominal pain or heavy bleeding indicating possible complications.

Before insertion, clinicians should assess suitability and counsel patients on risks.

• Screen for pregnancy: confirm the patient is not pregnant prior to placement.
• Assess uterine position: perform ultrasound to verify appropriate cavity size and orientation.
• Monitor for infection: watch for signs of pelvic infection in the weeks following insertion.
• Consider hormonal contraindications: avoid in women with active breast cancer, severe liver disease, or thromboembolic disorders.
• Counsel on follow‑up: schedule a check‑up six weeks after insertion and then annually.
• Store at ambient temperature: keep in original packaging, protect from moisture and direct sunlight.

Levonorgestrel released from Mirena can be affected by other medicines that alter hormone metabolism.

Major Interactions (Avoid)

• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine) may reduce contraceptive efficacy.
• Potent CYP3A4 inhibitors (e.g., ketoconazole) may increase hormone levels and side‑effect risk.

Moderate Interactions (Monitor Closely)

• Certain antibiotics (e.g., tetracycline) may slightly lower effectiveness.
• Anticonvulsants such as phenytoin may modestly decrease levonorgestrel concentrations.
• Herbal supplements like St. John’s wort may affect hormone metabolism and should be reviewed.