Neurocrine Biosciences has just completed phase II trials of elagolix (an oral GnRH antagonist) for endometriosis. It also recently announced a partnership with Abbott. The path through phase II was difficult, as Neurocrine struggled to find the appropriate endpoints with which to measure the effect of treatment on disease-associated pain. The drug is clearly active: it suppresses estradiol and interrupts the menstrual cycle — the intended pharmacological effects suggested by its mechanism of action. However, the goal of showing that therapy consistently relieves pain was more elusive and early trials showed mixed results. Encouragingly, the last trial in the series, Daisy PETAL, demonstrated robustly positive efficacy. But the pending question is whether Neurocrine has finally identified a winning set of parameters for designing phase III trials, or whether the difficulties seen throughout the earlier trials will continue to haunt further studies. If it succeeds in pivotal trials, elagolix will enter a competitive market with various agents used on and off label for endometriosis. But Neurocrine and Abbott are betting that elagolix’s differentiated safety profile will provide the market edge it needs to capture greater market share. We refer you to LifeTech’s report for our take on elagolix and its prospects.