Mirena is an intrauterine contraceptive that delivers small amounts of hormone directly to the uterus. Made of soft, flexible plastic, it is put in place by your healthcare provider during an office visit. Mirena is birth control that lasts as long as you want, for up to 5 years. Mirena works continuously, without a pill, without a daily hassle. Once Mirena is properly placed, all you have to do is check the threads once a month.