It hurts pretty bad because it will cause some cramping. With the IUDs I've heard really messed up things like anxiety attacks and depression, mood swings, just not being yourself mentally. Acne, hair loss, unpredictable weird periods. And a lot of chest pain complaints. The girl who sits next to me at work has one, and she is freakin' crazy, and moody and has all these mental issues. She even has medical leave for it. I tell her to take out her IUD, cause it sounds just like everyone else I hear. I mean, just read this, and its enough to say, "ok nevermind...let me find something else"
http://www.steadyhealth.com/Mirena_IUD_Side_Effects_t133005.html
http://www.lifetimemoms.com/family-parenting-tips/blog/mirena-iud-side-effects-or-am-i-crazy
I've heard similar things about the NuvaRing, which seems accurate as both are placed near your uterus and release the hormones directly to that part of your body (which to me would make most sense since that's the part of your body that needs it, where other bc's have to travel through your body). I'd never consider the shot, patch, or that silly thing they insert into your arm. It sucks that the only birth control without any side effects is a condom.