What are the side effects of the Mirena (levonorgestrel) Intrauterine Device (IUD)?

Side Effects of the Mirena (Levonorgestrel) IUD

The Mirena IUD commonly causes irregular spotting or light bleeding during the first 3-6 months of use, with bleeding generally decreasing over time, and many women eventually experiencing only light menstrual bleeding or amenorrhea. 1, 2

Common Side Effects

• Unscheduled spotting or light bleeding is expected primarily during the first 3-6 months of use and typically decreases with continued use 1
• Approximately half of users experience amenorrhea or oligomenorrhea by 2 years of use 2
• Heavy or prolonged bleeding is uncommon with levonorgestrel IUDs compared to copper IUDs 2
• Other potential side effects include:
  • Headaches 3
  • Nausea 3
  • Hair loss 3
  • Breast tenderness 3, 4
  • Depression 3
  • Decreased libido 3
  • Ovarian cysts 3, 4
  • Emotional lability 5
  • Weight gain 5
  • Acne 5

Bleeding Pattern Changes

• Bleeding generally decreases with continued use of the Mirena IUD 1, 2
• Many women eventually experience only light menstrual bleeding or complete absence of periods (amenorrhea) 1
• The bleeding pattern changes are due to the local effect of levonorgestrel on the endometrium 6
• Spotting may occur between periods, especially in the first few months 1

When to Seek Medical Attention

• New-onset spotting after a period of stable bleeding warrants evaluation for:
  • IUD displacement 1, 2
  • Sexually transmitted infections or pelvic inflammatory disease 1, 2
  • Pregnancy 1, 2
  • New pathologic uterine conditions such as polyps or fibroids 1, 2

Management of Side Effects

• For irregular bleeding:
  • Reassurance that bleeding irregularities are generally not harmful if no underlying problem is identified 1, 2
  • Counseling that bleeding patterns typically improve over time 1, 2
  • No specific medical treatments are recommended in guidelines for LNG-IUD users with irregular bleeding 2

Important Considerations

• The Mirena IUD is highly effective with a failure rate of less than 1% 5
• The primary mechanism of action is preventing fertilization by inhibiting sperm motility and thickening cervical mucus 5
• The 52-mg levonorgestrel IUD (Mirena) is approved for 5 years, although data suggest effectiveness for up to 7 years 5
• Continuation rates are improved when patients receive proper counseling about expected bleeding patterns 2
• Some women may request removal due to intolerance of amenorrhea or other side effects, despite the benefits 4

Contraindications and Cautions

• Current breast cancer (Category 4 - should not use) 5
• Past breast cancer with no evidence of current disease for 5 years (Category 3 - risks usually outweigh benefits) 5
• Persistently elevated β-hCG levels or malignant gestational trophoblastic disease (Category 4) 5

The Mirena IUD is generally well-tolerated, with most side effects being manageable and decreasing over time. The most common reason for early removal is irregular bleeding patterns, particularly during the initial months of use 5.