What are the side effects of the levonorgestrel-releasing intrauterine system (Mirena)?

Side Effects of Mirena (Levonorgestrel-Releasing Intrauterine System)

Mirena users most commonly experience bleeding irregularities (spotting, light bleeding, or amenorrhea), with hormonal side effects being relatively uncommon and rarely leading to discontinuation.

Primary Side Effects

Bleeding Pattern Changes (Most Common)

The dominant side effect profile of Mirena centers on menstrual changes 1:

• Irregular bleeding/spotting: Expected during the first 3-4 months of use
• Amenorrhea: Occurs in 10-37% of users after 9 months 2, representing a therapeutic effect rather than a complication
• Reduced menstrual blood loss: Progressive reduction is the norm, not a concern

Important counseling point: The 2024 CDC guidelines note that for LNG-IUD users with bleeding irregularities, no specific interventions are routinely recommended 1. This reflects the benign, self-limiting nature of these changes.

Hormonal Side Effects (Less Common)

Recent high-quality data from 2024 involving 1,714 women demonstrates that hormone-related side effects are infrequent 3:

• Acne: 8.5-13% of users (slightly higher in those switching from combined hormonal contraception)
• Headaches, nausea, breast tenderness: Each reported in <3% of users
• Mood changes, decreased libido: Uncommon (libido issues in 1.4-3.1%)
• Hair loss, depression: Rare
• Ovarian cysts: Occasional, typically asymptomatic

Critical finding: Only 5.5% of users discontinued Mirena due to these side effects over 6 months, with no difference between those previously using hormonal versus non-hormonal contraception 3.

Serious but Rare Complications

Device-Related Issues

• Expulsion: <5% of users 2, though rates up to 24% reported in adenomyosis treatment 4
• Perforation: <2% 2
• Pelvic inflammatory disease: Actually reduced compared to no contraception due to cervical mucus thickening and reduced menstrual blood 5

Allergic Reactions

• Acute urticaria: Extremely rare case reports exist 6, but this is not a common concern

Weight and Metabolic Effects

Weight gain is minimal and comparable to copper IUDs: approximately 500g per year over 5 years 5. This is substantially less than many users fear.

Clinical Management Algorithm

For bleeding irregularities 1:

1. Provide reassurance during first 3-4 months
2. If patient desires treatment: No specific interventions are recommended for LNG-IUD users (unlike copper IUD users who may benefit from NSAIDs)
3. If patient desires removal: Remove device and offer alternative contraception

For hormonal side effects:

1. Reassure that systemic hormone exposure is low
2. Most resolve within 6 months
3. Consider removal only if significantly impacting quality of life

Key Counseling Points

Before insertion, patients must understand:

• Amenorrhea after 9 months is common (10-37%) and not harmful 2
• Initial irregular bleeding for 3-4 months is expected
• True hormonal side effects are uncommon (<3% for most symptoms) 3
• The device is now FDA-approved for 8 years of use 2
• Pregnancy risk is exceptionally low (Pearl Index 0.13) 2

Common Pitfall to Avoid

Do not attribute every symptom to Mirena. The 2024 study showed that when comparing users to those with copper IUDs or no hormonal contraception, most symptoms occurred at similar rates 3. Only acne showed a clear association with LNG-IUD use. Consider alternative diagnoses for mood changes, weight gain, or other systemic symptoms before automatically attributing them to the device.