Hormone Type in IUD Contraceptives
Direct Answer
Hormonal IUDs contain levonorgestrel, a synthetic progestin (progestogen), which is released locally into the uterine cavity at a rate of approximately 20 micrograms per day. 1, 2
Hormone Specifications
Levonorgestrel as the Active Agent
Levonorgestrel is the only hormone used in hormonal IUDs currently available, distinguishing them from copper IUDs which contain no hormones at all. 3
The levonorgestrel-releasing IUD is classified as a progestin-only contraceptive method, meaning it contains no estrogen component. 3
Multiple formulations exist with different levonorgestrel doses: the 52 mg devices (Mirena, Liletta) and lower-dose options like the 13.5 mg device (Skyla). 1
Mechanism of Hormonal Action
Levonorgestrel works primarily by thickening cervical mucus to inhibit sperm motility and by suppressing endometrial growth, making the uterine lining less receptive. 1, 4
The hormone creates strong local suppression of the endometrium, rendering it insensitive to ovarian estradiol, which explains the reduction in menstrual bleeding. 4
Plasma concentrations of levonorgestrel range from approximately 260 pg/ml during the first three months to 129 pg/ml after one year of use, demonstrating continuous systemic absorption at low levels. 5
Clinical Distinction from Other Hormonal Methods
Unlike combined hormonal contraceptives (pills, patches, rings) that contain both estrogen and progestin, hormonal IUDs are progestin-only devices with no estrogen-associated risks. 3
This makes levonorgestrel IUDs particularly suitable for women with contraindications to estrogen, including those with antiphospholipid antibodies, history of thromboembolism, or decompensated cirrhosis. 3
The absence of estrogen means levonorgestrel IUDs can be safely used in breastfeeding women and those with cardiovascular risk factors where estrogen would be contraindicated. 6