Endometriosis is the presence of hormonally responsive endometrial tissue outside the uterine cavity. In terms of efficacy there is little to choose between the drugs licensed for this indication and product selection depends mainly on patient tolerability.
The side-effects of GnRH analogues mimic symptoms more normally associated with the menopause. Most patients will suffer from hot flushes and up to a quarter will experience a loss of libido, reduction in breast size and/or emotional lability. Although the GnRH analogues can cause a significant reduction in bone mass, this has not been correlated with an increased risk of bone fracture. Care should nevertheless be exercised in patients at risk of osteoporosis.
The progestogens norethisterone and medroxyprogesterone are associated with breakthrough bleeding and breast discomfort. Ovulation is suppressed in the majority of patients, but normal ovulatory cycles are usually resumed within two months of withdrawing oral therapy. With the depot preparation of medroxyprogesterone, anovulatory cycles can persist for 18 months post-therapy and this formulation is best avoided in women who wish to conceive. Progestogens can trigger water retention, changes in libido, blood lipid levels and liver function.
Some GnRH analogues are also licensed for the management of uterine fibroids (leiomyoma), benign tumours of uterine smooth muscle—either to reduce their size before surgery or when surgery is inappropriate. Alternatively, the progesterone receptor modulator ulipristal acetate can be given to reduce fibroid volume and control uterine bleeding for up to 3 months before surgery, or as intermittent treatment courses of 3 months. It is taken orally and seems to have less severe hypoestrogenic effects than GnRH analogues.