A gynecological illness caused by the abnormal presence of tissue that more or less perfectly resembles the lining of the uterus (endometrium) but growing outside of the uterus itself and distributed in other pelvic areas. Since this aberrant endometrial tissue responds to the hormone-induced changes of the woman's menstrual cycle but, unlike the true endometrial lining of the uterus, is entrapped in other tissue such as bone and muscle, its cyclic changes of menstruation, causes the problem to repress, and even after the pregnancy improvement is sometimes sustained for a period up to three or four years.
Since a surgical approach to the problem is not always practical or successful, the so called "contraceptive pill" has been recommended for use over prolonged periods to eliminate the cyclic changes of the menstrual cycle and thus eliminate the periodic pain of endometriosis. It should be noted, from a moral viewpoint, that although this progestational-estrogen type therapy is, in itself, essentially the same as that used in the "contraceptive pill," it is not used in theses cases as a contraceptive. the purpose of the therapy is to ameliorate a seriously abnormal and indeed pathological condition insofar as it is aggravated by hormonal changes of the menstrual cycle. Although temporary sterility is a side effect of the treatment, contraception is not the purpose, and thus the treatment in no way conflicts with Catholic teaching.