Mirena (Levonorgestrel)

Mirena, a levonorgestrel-releasing intrauterine system, is used in several gynecologic indications.

• Contraception: provides up to five years of highly effective pregnancy prevention by inhibiting ovulation and altering cervical mucus.
• Heavy menstrual bleeding: reduces menstrual blood loss by up to 80 % and improves anemia associated with excessive bleeding.
• Endometriosis-associated pain: alleviates chronic pelvic pain and dysmenorrhea related to endometriosis through local hormonal effects.
• Menstrual cycle regulation: can lead to lighter, more predictable periods in women without heavy bleeding.

• Mirena continuously releases levonorgestrel directly into the uterine cavity at approximately 20 µg per day. The progestin binds to progesterone receptors in the endometrium, suppressing ovulation, thickening cervical mucus to impede sperm passage, and inducing endometrial atrophy, which together prevent implantation of a fertilized egg. These local actions occur with minimal systemic exposure, allowing effective contraception while reducing systemic hormonal side effects.

Levonorgestrel released from Mirena may be associated with a range of adverse reactions, which are categorized by frequency and severity.

Common Side Effects

• Irregular bleeding or spotting: unpredictable bleeding patterns during the first months.
• Amenorrhea: absence of menstrual periods after prolonged use.
• Headache: mild to moderate intensity.
• Breast tenderness: discomfort or soreness in the breasts.
• Acne: worsening of skin lesions.
• Mood changes: irritability or depression.

Serious or Rare Side Effects

• Uterine perforation: rare injury to the uterine wall during insertion.
• Pelvic infection: severe infection requiring medical treatment.
• Ectopic pregnancy: pregnancy occurring outside the uterus if contraception fails.

Before Mirena insertion, clinicians should evaluate patients for specific contraindications and follow recommended safety measures.

• Assess for active pelvic infection: postpone insertion until infection is resolved.
• Screen for unexplained vaginal bleeding: investigate underlying causes before use.
• Evaluate pregnancy status: Mirena must not be placed in a pregnant woman.
• Review liver disease or hormone‑sensitive cancers: avoid use in patients with severe hepatic impairment or known breast cancer.
• Check for uterine anomalies: abnormal cavity shape may increase risk of expulsion or perforation.
• Store at room temperature below 25°C: keep in original packaging, protect from moisture and direct sunlight.

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

Major Interactions (Avoid)

• Enzyme inducers (e.g., rifampin, carbamazepine): may lower levonorgestrel levels and reduce efficacy.
• Antifungal azoles (e.g., ketoconazole): can increase levonorgestrel concentrations, potentially raising side‑effect risk.
• Certain antiretrovirals (e.g., efavirenz): may decrease contraceptive effectiveness.

Moderate Interactions (Monitor Closely)

• Concurrent hormonal contraceptives: may alter bleeding patterns but generally safe.
• Antibiotics such as tetracycline: unlikely to affect efficacy but monitor for changes in menstrual bleeding.