yes you are quite correct, Happiernow, mirena can raise blood glucose levels so is particularly dodgy for anyone with diabetes or at risk of diabetes.
To Katy21 - Anyone having side effects should get it out. although most side effects generally go after a while once it is removed, it can do permanent damage. People have even commited suicide because of the depression it has caused, and others have had their lives ruined and also ruined their chances of ever having any more children anyway, due to perforation of the uterus and other complications of the mirena.
Birth control HAS to be a secondary concern when your health and even your life is at risk. And to be honest, many people also get pregnant while having mirena inside them so it is not 100% effective, nothing is. Every time you have sex, you run a risk of getting pregnant, it's as simple as that. The only effective thing is not to have sex. But if people still want to have sex without health risk, the only safe way is to follow a non-hormonal method of birth control. Your local family planning clinic will be able to discuss all the possiblities with you. Many women on this forum use condoms, others use the "original" method of contraception - getting to know your body and knowing when you ovulate etc so you can work out your safest times of the month - there are books on the subject too, no doubt, from amazon. I use condoms and always have - i only had the mirena for a thickened uterus, not because i wanted or needed contraception. But i would rather live with that, and constant bleeding, than put that chemical back into my body.