I have the Kyleena IUD! I had it inserted about 8 months ago and love it. I’d say the only side effects I’ve had was in the 2 weeks following insertion. The cramps were pretty bad and had a decent amount of bleeding. However, since that 2 week period ended I haven’t had any symptoms at all - no bleeding, extremely rare cramping, etc,! Insertion did hurt a lot but it was a quick procedure (about 30 seconds max).
It’s just so nice not having to really worry about pregnancy at all for 5 years! But remember that everyone reacts differently to different forms of birth control so what works for me may not work for you.
