"when they tell you mirena can cause irregular periods, they&#039;re not joking. i had read a review that someone wrote saying they ruined every pair of underwear that wasn&#039;t black, &amp; they definitely were not joking either! before mirena i had very heavy periods, i mean super plus in 3 hours on day 1. mirena has lightened that tremendously! although in the past 2 months, something has gone haywire! last month, i had a 3 week long period. it would stop for one day, then kick start as if it&#039;s day 1 and on all over again. i am currently on my second week this month, so i called &amp; asked what i can do. they said there&#039;s nothing! it is a hormone, so it effects everyone differently. otherwise, i&#039;m not pregnant, &amp; my 3 wk periods are lighter!"