Does st.johns wort decrease the effectiveness of the skyla iud?

Such supplements that might affect oral birth control hormones should NOT affect effectiveness of IUDs. Kyleena, Mirena, and Skyla work by releasing a low-dose of levonorgestrel (a progesterone) which is thought to prevent pregnancy by thickening cervical mucus to help prevent sperm swimming into the uterus, inhibiting sperm motility and survival, and altering the characteristics uterine lining.