Copper
"Unfortunately my procedure didn't go like it should have, but I'm one of few who has had this happen so don't freak out.
But when it was inserted, it was sharp mild cramps but I had taken some pain killers before just to be safe and as they were cutting my strings, they had yanked a little and it was ripped out. The nurse and doctor apologized, saying they had miss measured me and didn't put it in all the way. So they redid the thing again. But, I must say I've loved it. I've had a few instances where I should have been pregnant but the IUD did it's job. Although, I worry a lot over possibilities of it failing, so use extra protection just in case. But so far works 100% for me"