Mids, as Lynx said you can easily have an IUD if you haven't had children, it's just perhaps a little more painful - the sounding and then insertion via the cervix is a very specific and unusual type of pain, but bearable! I know from personal experience, having had it done twice. I took a diazepam and co-codamol the first time, nothing the second.
And it is the same drug, but as it's only released into the uterus and cervix, it doesn't act systemically, thus you don't get the same level of side-effects as with the oral product.
I'll hold my hand up and say that while they're not for everyone, I'm very pro IUDs: no drugs, no side-effects (bar the initial discomfort and heavier periods for 4-5 months with the normal copper one), and they're virtually foolproof so long as they don't dislodge - and that normally happens in the first few weeks, when you should go back for a check-up anyway. Even if it were to fail at the first hurdle and a rogue sperm got through, no egg/embryo can implant. And they last 5-10 years!