I had posted previously about this. This past winter/spring I was researching the side effects and found a medical study stating that the hormone in Mirena, when taken in pill form, dramatically increases the chance of becoming insulin resistant. It listed the side effects which are many of the ones I experienced on Mirena (dizziness, lightheadedness, nauseua, fatigue are some of them.) Don't expect a doctor to tell you the Mirena can cause this because they will laugh at you, which mine did. Well I decided to have mine taken out and I have not had one of these particular symptoms since. To me, that is proof enough.
Please note, that I am 38 years old, fairly slender, low blood pressure, never had any Sugar related problems while I was pregnant or any other time of my life. I have absolutely no reason for this to have happened to my accept the Mirena.