Quantitative levonorgestrel plasma level measurements in patients with regular and prolonged use of the levonorgestrel-releasing intrauterine system.

Background: The levonorgestrel-releasing intrauterine system (LNG-IUS) is well accepted as an easy-to-use contraceptive with an excellent side-effect profile. It contains a reservoir of 52 mg of levonorgestrel (LNG) with continuous release of the steroid. Its contraceptive use is approved for 5 years.