Updated from 1:21 a.m. EDT

Neurocrine Biosciences ( NBIX) designed the latest phase II study of its endometriosis drug elagolix with so many endpoints that it shouldn't be surprising to discover that some of the efficacy measures succeeded while others failed.

A potential problem for Neurocrine, however, is that one of the endpoints that came up short was the primary, or main goal, of the study, while another was an endpoint suggested by the U.S. Food and Drug Administration.

Elagolix is the lead drug in Neurocrine's research pipeline and the asset that investors hope erases the stigma attached to the company stemming from the disastrous FDA rejection of its sleeping pill indiplon three years ago.

Neurocrine has already completed three phase II studies of elagolix in women diagnosed with endometriosis. Results from a fourth phase II study were announced Wednesday night, while a fifth study is expected to be completed in the third quarter.

With all this elagolix data, Neurocrine aims to get FDA approval for a phase III study program to start next year. Just as importantly, Neurocrine is looking to attract a large drug company to sign on as a worldwide development partner.

Endometriosis is a condition mainly affecting women of childbearing age that occurs when endometrial cells, which form the lining of the uterus, are deposited outside the uterus. Pain and bleeding can occur if or when these endometrial tissues start to grow in response to hormones.

Neurocrine's latest phase II study, which the company calls "702" or "Lilac Petal," enrolled 155 women with confirmed endometriosis and treated them for 12 weeks with one of two daily doses of elagolix or a placebo.

The primary endpoint of the study was a reduction in pelvic pain measured using a daily numeric rating scale. Neurocrine considered this endpoint -- suggested by the National Institutes of Health -- to be "exploratory" because the company had never used it before in a clinical trial of endometriosis patients.

Patients treated with elagolix reported improved daily pelvic pain scores compared with placebo, but the difference wasn't statistically significant, Neurocrine reported Wednesday.

Elagolix also failed to demonstrate benefit over placebo using a daily measure of non-menstrual pelvic pain. The FDA asked the company to include this experimental endpoint in the study.

Elagolix did show strong, statistically significant efficacy when the drug was evaluated using monthly scores of pain reduction and other endometriosis symptoms that have been well validated in previous studies. Treatment with elagolix significantly reduced severe abdominal pain during menstruation compared to treatment with placebo, the company said.

"It is clear from this study and all of our previous studies that elagolix is a safe and effective treatment for endometriosis sufferers," said Kevin Gorman, Neurocrine's president and CEO. "This Phase II study provides the information we need to continue to move this program forward. While limitations were discovered in some of the new exploratory efficacy measures, elagolix again showed strong efficacy in the historical validated endometriosis measures, with an excellent safety profile."

Neurocrine said it would consult with the FDA about how to reconcile the differences seen when pain reduction was measured using daily and monthly scales.

Neurocrine shares closed Wednesday at $3.97, ahead of the elagolix data release, and were recently falling 7.3% to $3.68.

Know what you own: Other companies with endometriosis drugs in development include Abbott Labs ( ABT), Repros Therapeutics ( RPRX) and Aeterna Zentaris ( AEZS).
At the time of publication, Feuerstein's Biotech Select model portfolio had no positions in the stocks mentioned.

Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.