I am not a doctor. That said, my understanding is that IUDs are one of the best contraceptive methods out there. They have a bad reputation because they had issues when they were initially introduced, and they haven't quite overcome that reputation yet even though modern ones are excellent. There are non-hormonal ones too (pure copper), so it can avoid a whole host of side effects that some women experience with hormonal birth control. However they can also cause heavier periods with some people. Otherwise they seem to be the model of what you'd want a contraceptive to be (excellent effectiveness, safe, easily reversible, and forgettable–they last years and years).