Does anyone know any effective pain relievers for Endometriosis pain?

My best friend has Endometriosis. She is constantly in pain, and I would appreciate any advice as to how this can be remedied whether it be prescribed medicine, natural medicine, herbs, spices, I'll cut off my own hand if it would help her. I have read a little bit and I hard that Evening Primrose Oil might help. Does anyone have any ideas? Relaxing music and things of that nature are out; that kind of thing doesn't help an impatient cynic. Thank you very much for your help.