A Plain Language Summary to learn about relugolix combination therapy for the treatment of pain associated with endometriosis

What is this summary about?: This is a summary of research studies (known as clinical trials) called SPIRIT 1 and SPIRIT 2. The SPIRIT 1 and SPIRIT 2 studies compared how well a medicine called relugolix combination therapy worked in relieving pain in women with moderate to severe endometriosis compared to a placebo, a pill with no active medication. Endometriosis occurs when tissue similar to what normally lines the uterus grows in other places, such as the ovaries, fallopian tubes, and bowels.

What were the results?: Researchers looked at 1261 adult women with moderate to severe endometriosis. Randomly, 420 (33%) of these women were assigned to relugolix combination therapy, 420 (33%) were assigned to delayed relugolix combination therapy (relugolix alone first and then relugolix combination therapy for the remainder of the study), and 421 (33%) were assigned to placebo. The SPIRIT 1 and SPIRIT 2 studies showed that more women taking relugolix combination therapy (75% from SPIRIT 1 and 75% from SPIRIT 2) for 24 weeks had both less pelvic or groin pain during menstrual periods from endometriosis and no need for more pain medicines than women who took placebo (27% from SPIRIT 1 and 30% from SPIRIT 2). The SPIRIT 1 and SPIRIT 2 studies also showed that more women taking relugolix combination therapy (59% from SPIRIT 1 and 66% from SPIRIT 2) for 24 weeks had both less pelvic or groin pain between menstrual periods from endometriosis and no need for more pain medicines than women who took placebo (40% from SPIRIT 1 and 43% from SPIRIT 2). Women taking relugolix combination therapy had less pelvic or groin pain during and between menstrual periods within 4 weeks of starting the medicine. The most common side effects were headaches, the common cold, and hot flushes or feeling hot among women taking relugolix combination therapy, delayed relugolix combination therapy, and placebo. Relugolix combination therapy was considered safe for those with no major medical problems. Women taking relugolix combination therapy had little to no loss of bone mineral density (a way of knowing how strong bones are) after 24 weeks of treatment.

What do the results of these studies tell us?: Women with moderate to severe endometriosis taking relugolix combination therapy had much less pain from endometriosis than women taking placebo. Clinical Trial Registration: NCT03204318 (SPIRIT-1); NCT03204331 (SPIRIT-2) (ClinicalTrials.gov).