In another report, 129 adolescent girls with endometriosis received progesterone for 11 months – with some positive effects in terms of relief fo pain. The mechanism may be through reductions in blood flow. Side effects included headache, nausea, hot flushes and acne.
http://www.internalmedicinenews.com/news/adolescent-medicine/single-article/norethindrone-acetate-eases-pain-bleeding-in-teen-endometriosis/fef48a50b3.html
It does appear that these young women are in significant difficulty. The next prescription was commonly for anti-GnRH agonists (menopausal treatment) to attempt to control their pain. No mention of bowel habits at any stage. No mention of Mirena IUS.