What are the potential adverse drug reactions (ADRs) associated with the Mirena (levonorgestrel) implant in females of reproductive age?

Mirena (Levonorgestrel IUD) Adverse Drug Reactions

The most common adverse reactions with Mirena are menstrual bleeding pattern changes (including amenorrhea, irregular bleeding, and spotting), with other less common but notable side effects including headache, acne, breast tenderness, weight gain, and ovarian cysts. 1

Menstrual Bleeding Changes (Most Common)

Bleeding irregularities are the most frequent adverse effect and the primary reason for device discontinuation. 1

Expected Patterns:

• Many women (approximately 64%) experience amenorrhea or infrequent bleeding over the first 2 years, which is generally considered a therapeutic benefit rather than a harmful effect 1
• Approximately 15% report frequent or prolonged bleeding, particularly in the first 3-6 months 1
• Unscheduled spotting or light bleeding is common, especially initially, and typically decreases with continued use 1
• In 93.7% of cases, spotting disappears within six months 2

Clinical Pitfall:

Unscheduled bleeding can also indicate an STI or other gynecological pathology (polyps, fibroids), not just a device side effect—always consider screening for STIs, particularly in adolescents. 1

Systemic Adverse Effects

Common (Probably Related):

• Headache - most frequent systemic adverse event 3
• Acne - frequently reported 1, 3
• Breast tenderness - commonly reported 1, 2

Less Common but Possible (Possibly Steroid-Related):

• Weight gain 1, 3
• Emotional lability/mood changes 1, 3
• Dizziness 3
• Loss of libido 3
• Fatigue 3
• Hair loss 3

Ovarian Cysts

Persistent ovarian follicles (functional cysts) are a common event during progestin-only contraceptive use and spontaneously disappear without intervention. 3

• Providers should be aware of this condition to avoid unnecessary surgical interventions 3
• Transient ovarian cystic images were observed in clinical experience 2

Insertion-Related Adverse Reactions

Insertion of Mirena is associated with more difficulty and adverse reactions compared to copper IUDs. 4

Specific Insertion Issues:

• Difficult insertion reported 2.7 times more often than with copper IUDs 4
• Pain and vasovagal reactions more frequent during insertion 4
• Mechanical device problems occur in approximately 1% of insertions 4
• About 2% of insertions require general anesthetic 4

Post-Insertion Complications:

• Small risk of pelvic infection limited to first 20-21 days after insertion 1, 5
• Expulsion or dislocation can occur, typically within first 8 months 2

Rare but Serious Reactions

Acute urticaria (hives) has been reported following Mirena implantation, though rare. 6

• One documented case involved whole-body urticaria with pruritus, lower quadrant pain, and dizziness occurring 2 hours post-insertion 6
• Required immediate device removal and corticosteroid treatment 6

Drug Interactions

Efficacy may be impaired by hepatic enzyme-inducing drugs acting on the cytochrome P450 pathway. 1

• Specific concern with efavirenz (HIV medication), nevirapine, and most protease inhibitors 1
• Contraceptive failures have been described in women receiving efavirenz-containing antiretroviral therapy 1

Bone Mineral Density Considerations

Data are scant on the effect of levonorgestrel IUDs on bone mineral density, though concerns are less than with DMPA given higher estradiol levels in IUD users. 1

Contraindications (When NOT to Use)

Current or recent (past 3 months) pelvic inflammatory disease is an absolute contraindication. 1, 5

Key Counseling Point

Enhanced pre-insertion counseling about expected bleeding patterns significantly reduces discontinuation rates—patients must understand that amenorrhea and irregular bleeding are expected, not harmful, and may not improve over time. 1, 7