AIM: To determine the optimal interval of injections of intramuscular depot medroxyprogesterone acetate 150 mg in the long-term treatment of endometriosis-associated pain.

METHOD: 112 patients with symptomatic endometriosis were randomized to receive either injections every month for 6 months, then every 3 months for a total of 15 months or injections every 3 months for 15 months. The primary outcome measure was patients' satisfaction.

RESULT: At months 3, 6, 9, 12 and 15 of the treatment phase, there was no statistically significant difference of percentages of patients with satisfaction between the two regimens (85.7 vs. 76.8%, 76.8 vs. 73.2%, 66.1 vs. 58.9%, 60.7 vs. 55.4%, 60.7 vs. 55.4%, respectively).

CONCLUSION: The optimal interval of injections of depot medroxyprogesterone acetate 150 mg is every 3 months.