Mirena, a plastic IUD which releases the hormone levonorgestrel to prevent pregnancy, is advertised as effective for five years, but is effective for at least seven years, according to the review published in the journal Contraception.

What can make Mirena less effective?

Mirena Interactions

Drugs and herbal supplements can make Mirena less effective. Examples of these substances include some blood thinners, anti-anxiety drugs and anti-seizure medications. Anti-retroviral drugs, antibiotics and St. John's Wort may also interact with Mirena.

Do Mirena IUD lose effectiveness?

Mirena can remain within the uterus and prevent pregnancy for 5 years. Skyla, another hormonal IUD, remains effective for up to 3 years. The different types release different quantities of hormones each day, and the amount decreases over time.