2 answers. 1) if you are asking if it is painful, then mildly so, and only for a very short time during and after insertion 2) if you are asking if it causes harm to the uterus or affects future ability to get pregnant and carry a child, then the answer is no.
Sometimes. Insertion of the Mirena (levonorgestrel) in a person never having a child could cause some discomfort.. Most physicians will advise you to take a non steroidal(motrin, Aleve etc) 30 minutes prior to the procedure to help with the craming. In my experience this works very well since the produre take less than a few minutes.