The hormone in Mirena is not Progesterone. It is Progestin. Many woman are mislead by this. They do both have the same direct effect, but the side effects are very different. Progestin is man made. Progesterone has great side effects for your body such as; balance fluid cells to prevent hypertension and bloating, helps protect against breast cancer, balanced levels of Progesterone help with mood, concentration, help with sex drive, has a beneficial effect of helping the body use and eliminate fats.
Progestin on the other hand may cause; fluid retention, breast tenderness, weight changes, acne, depression, insomnia, headaches. Has the opposite effect on the body to help with fats.
Progesterone is a natural hormone and the body eliminates it as needed. Progestins are not well processed by the body.
Basically, The reactions of Progestin are not consistent with that of Progesterone.
So, to wrap it up. What your body naturally produced while pregnant, is nothing like when Progestin is used.
We really need to be well educated as women when it comes to our bodies. We cannot believe everything just because a doctor or a drug company tells us. Our bodies' health is so very important in so many ways!