@cheebdragon: Yes; they all have potential side-effects. IUDs are recommended primarily for women who have already had a child, because the uterus changes after having been streched out and then recovering to normal size. There is a greater risk of uterine injury with an IUD/IUC if the woman has never given birth. The risk was also greater with the older devices, like the copper T, than with the new plastics.
Any hormone now has to warn of the risk of blood clots, whether it’s the pill, patch, nuva-ring (which I’ve heard good things about), or the shots. Even the Mirena which uses very low dose localized hormones has to list it.
None of them is 100% effective. I got pregnant while taking the pill and I got pregnant when a condom broke.
@Celest00: Your mother’s IUD was different from those available today. But you are correct – abstinence is the only 100% way to prevent pregnancy and STIs.