Unlike the copper coil, a mirena coil releases the hormone progesterone to prevent pregnancy. Known as an intrauterine system (IUS) it can stay in place for three to five years, compared to the IUDs five to ten year lifespan.
Because of the presence of progesterone, some women can experience headaches, acne, mood changes and breast tenderness after having the mirena fitted. These side effects are not associated with the copper coil.