Mirena IUD: Effects and contraindications

The Mirena intrauterine device (IUD) is a levonorgestrel-releasing intrauterine system (LNG-IUS) widely used for contraception and for management of heavy menstrual bleeding. Because it releases a progestin directly into the uterine cavity, circulating hormone concentrations are low compared with systemic hormonal contraceptives. This local delivery profile results in a high contraceptive efficacy with a relatively low frequency of systemic side effects. This article reviews the mechanism of action, expected effects, common and uncommon adverse events, contraindications, special considerations for insertion and removal, and practical guidance for counseling and management.

Sources used for this review include guidance and patient information from the American College of Obstetricians and Gynecologists (ACOG), the National Institutes of Health (NIH), the Mayo Clinic, and the Cleveland Clinic.

Mechanism of action

The Mirena IUD contains 52 mg of levonorgestrel and releases approximately 20 micrograms per day initially, with gradual decline over time. Its contraceptive effect is mediated by several local mechanisms:

Thickening of cervical mucus, which reduces sperm penetration.
Suppression of endometrial proliferation, creating an endometrium that is less receptive to implantation.
Local inhibition of sperm function within the uterine cavity and fallopian tubes.

Because levonorgestrel is delivered locally, systemic concentrations are substantially lower than with combined oral contraceptives or progestin-only pills. This pharmacologic profile underlies the comparatively low incidence of systemic progestin-related adverse effects in most users (ACOG; Mayo Clinic).

(ACOG Practice Bulletin; Mayo Clinic patient information)

Indications and clinical uses

Primary indications for Mirena include:

Long-acting reversible contraception (effective for up to 5 years for contraception; some evidence supports effectiveness for up to 6 years in certain circumstances).
Treatment of heavy menstrual bleeding (idiopathic menorrhagia); Mirena is approved for reduction of menstrual blood loss and often produces amenorrhea or hypomenorrhea in long-term users.
Part of management in selected gynecologic conditions where local progestin effect is beneficial (e.g., endometrial hyperplasia without atypia in selected patients under close supervision).

Efficacy for contraception is comparable to other long-acting methods and superior to short-acting methods such as daily pills, patches, or rings (Cleveland Clinic; ACOG).

Pattern of bleeding and menstrual changes

Changes in bleeding patterns are the most common and clinically significant effects associated with Mirena.

During the first 3 to 6 months after insertion, irregular bleeding and spotting are common. This may be frequent and unpredictable and is the most frequent reason for early removal.
Over time, the endometrium becomes atrophic in many users. By 12 months, many users experience reduced menstrual bleeding; a substantial proportion will have amenorrhea (absence of bleeding).
For users who receive Mirena specifically for heavy menstrual bleeding, reduction in menstrual blood loss typically occurs within several months and continues with ongoing use.

Patients should be counseled that early irregular bleeding is expected and often improves with continued use. If bleeding is heavy, persistent (>3–6 months), or accompanied by other symptoms (fever, severe pain), evaluation is warranted to exclude expulsion, infection, or other pathology (ACOG; NIH).

Common side effects

Because systemic exposure to levonorgestrel is low, the frequency of systemic side effects is generally lower than with systemic progestin-only or combined hormonal methods. However, some users experience:

Irregular bleeding or spotting (most common).
Abdominal or pelvic pain, particularly around the time of insertion.
Headache.
Breast tenderness.
Acne or changes in skin condition.
Mood changes, including depressive symptoms in a minority of users.

Most of these effects are mild-to-moderate and resolve or improve over time. Counseling about expected timing and course is important to improve continuation rates (Mayo Clinic; Cleveland Clinic).

Weight

Many patients ask whether Mirena causes weight gain. The available evidence does not demonstrate a clinically significant effect of the levonorgestrel IUD on body weight. Clinical studies and post-marketing surveillance have not shown greater weight change in Mirena users compared with non-users or users of other contraceptive methods. Individual weight fluctuations occur for multiple reasons and should not be attributed solely to the IUD without a broader clinical assessment (Mayo Clinic; NIH).

Acne and seborrhea

Changes in acne can occur with progestin exposure. For most users of Mirena, acne—if it develops—is mild and transient. Management follows standard dermatologic approaches (topical agents, oral medications when indicated). If acne is severe or persistent and suspected to be related to the device, removal may be considered after discussion of risks and benefits (Cleveland Clinic; ACOG).

Headaches and migraine

Mild episodic headache is common in the general population and is not typically exacerbated by Mirena. However, new-onset severe or persistent migraine-type headaches—particularly with focal neurologic symptoms—require evaluation. ACOG and other guidelines advise consideration of device removal if severe migraine with aura develops or if migraines worsen significantly after insertion; neurological evaluation should follow removal where indicated.

Serious but uncommon adverse events

While serious complications are rare, they can occur and require prompt recognition and management.

Uterine perforation

Perforation of the uterus by the device can occur at the time of insertion or, rarely, subsequently.
Reported rates vary but are generally low (approximately 1–2 per 1,000 insertions). Risk factors include clinician inexperience and insertion during the postpartum period when the uterine wall may be softer.
If perforation is suspected (severe pain at insertion, no visible strings, abnormal bleeding, or imaging showing device outside the uterine cavity), prompt evaluation with pelvic examination and ultrasound is required; laparoscopic removal may be necessary (ACOG; Cleveland Clinic).

Expulsion

Partial or complete expulsion of the device can occur, most commonly within the first months after insertion.
Nulliparity, insertion immediately postpartum, and heavy menstrual bleeding are among factors that may increase expulsion risk.
Expulsion presents with a return of menstrual fertility patterns, pelvic pain, or absence of strings at the cervical os. If expulsion is suspected, a pelvic exam and ultrasound are indicated. If complete expulsion has occurred, another device can be inserted if desired, or alternative contraception chosen (ACOG; Mayo Clinic).

Pelvic inflammatory disease (PID) and infection

The risk of pelvic infection associated with IUD insertion is primarily concentrated in the first 20 days after insertion and relates mainly to pre-existing sexually transmitted infection at the time of insertion.
Current purulent cervicitis, untreated sexually transmitted infections, or known pelvic infection are contraindications to insertion.
Routine screening for chlamydia and gonorrhea per risk-based recommendations prior to insertion is advised. If PID occurs in a user, standard treatment is required; the device may be removed if symptoms are severe, if infection does not respond to therapy, or if tubo-ovarian abscess develops (ACOG; CDC guidance).

Ectopic pregnancy

While the absolute risk of pregnancy is low with Mirena, if pregnancy occurs with an IUD in place, there is a relatively higher proportion of ectopic pregnancies among those pregnancies than among unprotected pregnancies.
Importantly, Mirena reduces the overall risk of pregnancy—including ectopic pregnancy—relative to non-use. However, clinicians must consider ectopic pregnancy in any user presenting with positive pregnancy test and pelvic pain or abnormal bleeding (ACOG; Mayo Clinic).

Device malposition and pain

Malposition of the device within the uterine cavity can cause pain, bleeding, or reduced contraceptive efficacy. Pelvic ultrasound is the imaging modality of choice to assess position.

Contraindications and conditions requiring caution

Clinical contraindications to Mirena use are based on the risk that levonorgestrel release or the presence of an intrauterine foreign body would worsen an existing condition or increase the risk of serious outcomes. Absolute and relative contraindications are summarized below; clinical decisions should rely on guideline-based evaluation (ACOG; NIH; Mayo Clinic).

Absolute contraindications (device should not be used):

Known or suspected pregnancy.
Current purulent cervicitis or sexually transmitted infection (e.g., chlamydia, gonorrhea).
Current pelvic inflammatory disease (PID) or recent (within 3 months) postpartum endometritis.
Known or suspected uterine or cervical malignancy (undiagnosed abnormal uterine bleeding should be evaluated before insertion).
Known or suspected progestin-sensitive malignancy (e.g., current breast cancer). Use of levonorgestrel-containing devices is generally not recommended in women with active breast cancer; assessment and individualized counseling are necessary.
Distortion of the uterine cavity, including large fibroids that deform the cavity or significant uterine anomalies that preclude proper device placement.
Acute liver disease or liver tumor (because systemic hormone metabolism is hepatic; severe hepatic impairment is a contraindication).
Known hypersensitivity to levonorgestrel or the device components.

Conditions requiring caution or individualized assessment (may be acceptable in some cases under medical supervision):

History of ectopic pregnancy (Mirena reduces absolute pregnancy risk but if pregnancy occurs the relative risk of ectopic is higher).
History of pelvic inflammatory disease (risk may be acceptable if no current infection and no high risk of STIs).
Hypersensitivity or severe metabolic disease that may be exacerbated by progestin exposure; individualized counseling is required.
Unexplained vaginal bleeding: evaluate thoroughly before insertion to rule out structural or neoplastic causes.

Specific note on cervical dysplasia and cervical intraepithelial neoplasia (CIN):

Detection of cervical dysplasia (CIN) on cytology alone is not an absolute contraindication to Mirena insertion. However, active, untreated cervical cancer is an absolute contraindication. Appropriate gynecologic evaluation and treatment of significant cervical disease should precede insertion in many cases (ACOG).

Providers should consult current medical eligibility criteria and practice bulletins for detailed guidance on specific clinical scenarios; patient counseling should emphasize both benefits and potential risks (ACOG; NIH).

Timing of insertion: postpartum, breastfeeding, and adolescents

Immediate postpartum insertion (within 10 minutes of placental delivery) is an option and provides immediate contraception but carries a higher risk of expulsion compared with delayed insertion (for this reason many clinicians advise delayed insertion if feasible).
In breastfeeding patients, the LNG-IUS is considered compatible with breastfeeding. Levonorgestrel levels in breast milk are minimal, and data do not demonstrate adverse effects on lactation or infant growth; however, insertion technique and timing considerations apply (ACOG; WHO statements).
Mirena is appropriate for use in adolescents and nulliparous women. Long-acting reversible contraception (LARC), including the LNG-IUS, is considered first-line for adolescents by multiple professional organizations due to high efficacy and safety when appropriately counseled and inserted (ACOG; CDC).

Insertion and removal: procedure and practical considerations

Insertion:

Insertion is performed in an outpatient setting by a trained clinician. A pelvic examination is performed, and uterine size and position are assessed. A sterile technique is used.
Pain at insertion is common; options for analgesia include local cervical anesthesia, oral analgesics, and pre-procedure counseling. For most patients, no anesthesia or simple analgesics suffice.
Following insertion, the clinician trims the device strings to an appropriate length and advises the patient on how and when to check strings.

Follow-up:

Routine follow-up within 4–12 weeks may be scheduled to assess tolerance and verify string position; routine ultrasound is not required unless clinically indicated (e.g., missing strings, pain).
Patients should be counseled on signs that require immediate evaluation (severe pelvic pain, fever, heavy bleeding, symptoms of pregnancy, or missing/shortened strings).

Removal:

Removal is a simple in-office procedure that involves grasping the strings and gently withdrawing the device. Fertility typically returns rapidly after removal, with ovulation resuming in most cases within weeks to months.
If strings are not visible or cannot be palpated, ultrasound localization is recommended; hysteroscopic or laparoscopic retrieval may be necessary for nonvisible devices or when removal is complicated by embedment or perforation.

Drug interactions

Because systemic levonorgestrel exposure is low, clinically significant interactions are uncommon. Potent hepatic enzyme inducers (e.g., rifampin, certain anticonvulsants) can reduce circulating steroid concentrations; however, the clinical significance for intrauterine systems is less clear than for systemic hormones. When patients are taking potent enzyme inducers, clinicians should evaluate contraceptive reliability and consider alternative or additional contraceptive measures if necessary. Always review current drug interaction guidance for specific medications (NIH; manufacturer information).

Management of common adverse effects

Irregular bleeding: Reassure patients that irregular bleeding is common in the first 3–6 months. If bleeding is bothersome or persistent beyond this period, evaluate for causes (infection, expulsion, uterine pathology). Short courses of nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce bleeding and cramping in some patients; in specific cases, a combined oral contraceptive or tranexamic acid may be used under clinician guidance.
Cramping/pain: NSAIDs are first-line for procedural or cyclical cramping. If severe or persistent pain occurs, assess for expulsion, malposition, or other pathology.
Acne or breast tenderness: Manage according to symptom severity; consider dermatologic therapies for acne or removal if symptoms are severe and persistent.
Mood changes: Evaluate for underlying mood disorders and monitor symptoms. If new-onset or worsening depression occurs and is attributable to the device after careful assessment, removal may be considered.

Decisions about intervention or removal should be individualized, taking into account the severity of symptoms, contraceptive needs, and patient preferences (ACOG; Mayo Clinic).

Fertility after removal

Return to fertility after Mirena removal is typically rapid. Most individuals ovulate within weeks to months after removal and pregnancy rates after removal are comparable to the population baseline. Mirena does not have a prolonged negative effect on fertility for the majority of users (Cleveland Clinic; ACOG).

Counseling and informed consent

Prior to insertion, clinicians should provide comprehensive counseling that includes:

Expected efficacy for contraception and potential non-contraceptive benefits (e.g., reduction in menstrual blood loss).
Likely changes in bleeding patterns and the typical time course for improvement.
Common side effects and signs of serious complications that warrant immediate evaluation (e.g., severe pelvic pain, fever, missing strings, pregnancy symptoms).
Contraindications specific to the patient’s medical history (e.g., active breast cancer, untreated pelvic infection).
Alternatives to LNG-IUS, including other contraceptive options and treatments for heavy menstrual bleeding.
The process of insertion and removal, including potential discomfort and the need for follow-up.

Involving patients in shared decision-making helps align contraceptive choice with individual health priorities and risk tolerance. Documented informed consent is recommended.

When to seek urgent evaluation

Advise patients to seek prompt medical care if they experience:

Signs or symptoms of pregnancy (positive pregnancy test, amenorrhea, new pelvic pain).
Severe pelvic or abdominal pain that is new or worsening.
Fever, chills, or purulent vaginal discharge (suggesting infection).
Heavy vaginal bleeding or passage of the device.
Missing or shorter-than-expected strings (which could indicate expulsion or device migration).

Early evaluation improves outcomes for treatable complications and helps preserve reproductive health and contraceptive efficacy (ACOG; Mayo Clinic).

Special clinical scenarios

Women with prior cesarean delivery: Mirena may be used; perforation risk is not clearly increased by prior cesarean, but individual anatomy should be assessed.
Women with fibroids: Small intramural fibroids that do not distort the uterine cavity are not an absolute contraindication. Fibroids that deform the cavity may prevent correct device placement or increase expulsion risk and are generally a contraindication to IUD placement.
Women with complex medical histories: Collaborate with specialty care as needed (e.g., oncology for women with recent breast cancer, hepatology for significant liver disease).

Summary

The Mirena levonorgestrel-releasing intrauterine system is an effective long-acting contraceptive that also provides therapeutic benefit for heavy menstrual bleeding. Because it delivers levonorgestrel locally, systemic hormone exposure is low; most systemic side effects are uncommon, and many users experience reduced menstrual bleeding over time. The most frequent short-term effect is irregular bleeding in the first months after insertion. Serious complications—such as uterine perforation, device expulsion, pelvic infection, and, rarely, ectopic pregnancy—are uncommon but require prompt recognition and management. Contraindications include current pregnancy, active pelvic infection, known or suspected uterine or cervical malignancy, active breast cancer, significant distortion of the uterine cavity, and severe liver disease. Appropriate pre-insertion evaluation, counseling, and post-insertion follow-up optimize safety and patient satisfaction.

For individualized recommendations, patients should consult their clinician and refer to current professional guidance, including ACOG practice bulletins and relevant national clinical resources.

References

American College of Obstetricians and Gynecologists (ACOG). Practice Bulletin: Long-Acting Reversible Contraception: Implants and Intrauterine Devices. ACOG Practice Bulletin (various years). https://www.acog.org
MedlinePlus (U.S. National Library of Medicine / NIH). Levonorgestrel intrauterine device (Mirena). https://medlineplus.gov
Mayo Clinic. Mirena (intrauterine device) - Patient information. https://www.mayoclinic.org
Cleveland Clinic. Mirena IUD: Uses, Side Effects, and More. https://my.clevelandclinic.org

(For the most up-to-date clinical guidance, consult the full ACOG practice bulletins and national contraceptive medical eligibility criteria.)