Levonorgestrel
"I got the mirena fitted on the 13th Feb, having it fitted wasn't to bad, just felt a little uncomfortable. But after, it was fitted I did experience the worse cramps ever, it was so painful - I've never had children so I don't know if it was because of that. 
I bled consecutively for 4 weeks, heavy bleeding for 1 then really light, spotting for 3. However I didn't have a single cramp.

Soon after that, I've had no bleeding, no pains. No periods since so it seems to be doing the job, I think you've just got to persevere with it and let it get use to your body before you start criticising it. However it doesn't work for everyone :)"