Mirena Side Effects: What to Expect and When to Call Your Doctor

One of the most common questions patients have about Mirena is: what side effects should I expect? Knowing what's normal — and what's a warning sign — helps you feel confident after insertion and know when to seek medical care. Here's a complete, honest guide to Mirena's side effects.

Common Side Effects of Mirena (Usually Temporary)

Most people who use Mirena experience at least some of these side effects, particularly in the first 3–6 months. They typically improve over time:

• Irregular bleeding or spotting — The most common side effect. During the first 3–6 months, you may experience unpredictable light bleeding or spotting between periods. This is the most frequent reason patients consider removing Mirena early, but it typically resolves.
• Pelvic cramping or pain — Cramping during and after insertion is normal and usually lasts a few hours to a few days. Some mild cramping may continue for 2–4 weeks.
• Headache — Reported by some patients, especially in the first few months.
• Acne — Levonorgestrel is an androgenic progestin, and some patients notice increased acne, particularly in the first few months.
• Ovarian cysts — Follicular cysts can develop. Most resolve on their own within 1–3 months without treatment.
• Mood changes — Some patients report mood changes, depression, or decreased libido. Recent research has explored the relationship between hormonal IUDs and depression risk.
• Breast tenderness — Mild and usually temporary.
• Nausea — Less common; may occur in the first few weeks.

Changes to Your Period: What's Normal with Mirena?

Mirena has a well-known effect on menstrual cycles. Here's what to expect over time:

• First 3–6 months: Irregular spotting is very common — you may bleed more days than usual, but lightly.
• 6 months to 1 year: Bleeding typically becomes much lighter. About 20% of Mirena users have no period at all after one year.
• After 2 years: Approximately 60% of Mirena users have no menstrual period.

Amenorrhea (no period) with Mirena is not harmful — it occurs because Mirena thins the uterine lining. There is no build-up of uterine lining that needs to be shed.

Serious Side Effects: Warning Signs That Need Immediate Attention

While serious side effects are rare (less than 1% of users), it's critical to know the warning signs:

• Signs of ectopic pregnancy: Severe one-sided pelvic pain, unusual vaginal bleeding, shoulder pain, or feeling faint. If pregnancy occurs with Mirena in place, up to 50% may be ectopic. Seek emergency care immediately.
• Signs of pelvic inflammatory disease (PID): Fever, chills, increased pelvic pain, unusual discharge. PID occurs in less than 1% of Mirena users, most often in the first year.
• Signs of uterine perforation: Severe cramping after insertion, inability to feel the IUD threads, or persistent deep pain. This is most common during or shortly after insertion, especially in recently postpartum or breastfeeding women.
• Signs of expulsion: Feeling the device, change in thread length or position, increased cramping or pain. If you suspect expulsion, avoid intercourse and contact your provider.
• Sepsis: Rare but serious — high fever, confusion, rapid breathing, organ symptoms. Seek emergency care immediately.

How to Check Your Mirena Threads at Home

Bayer recommends checking your Mirena threads once a month to confirm the device is in place. After your period (or once a month if you don't have periods), gently insert a clean finger into your vagina and feel for the two threads that should extend through your cervix. If you cannot feel the threads or feel the hard plastic of the device, contact your provider. Do not pull the threads.

When to Call Your Doctor

Call your healthcare provider if you experience:

• Severe pelvic or abdominal pain that doesn't improve
• Fever or signs of infection after insertion
• Heavy bleeding (soaking more than one pad per hour)
• Pregnancy symptoms or a positive pregnancy test
• Inability to feel Mirena threads or feeling the hard device
• Mood changes that significantly affect your daily functioning

For more on what to watch for with Mirena, see our guide to Mirena drug interactions and what to avoid.