Several trials have addressed the relative efficacy of combined GnRH-agonist and add-back therapy (with estrogen and progestogen) as compared with GnRHagonist treatment alone during six-month treatment periods. In general, pain was relieved as effectively with the combination as with a GnRH agonist alone, and the add-back therapy substantially reduced the side effects of the GnRH agonist. The results were similar in two longer trials of approximately one year in duration. It seems clear that add-back therapy can be used in combination with GnRH-agonist treatment without a loss of efficacy and with a substantial amelioration of hypoestrogenic symptoms. This seems to be the case even when the add-back therapy is
begun during the first month of treatment, suggesting that it is unnecessary to include an interval without add-back therapy at the beginning of a treatment cycle.