A new drug with the potential to treat endometriosis-associated pain with very few side effects is getting closer to official approval.

Endometriosis is a chronic inflammatory condition and the leading cause of pelvic pain worldwide. With no known cause or cure, many patients have run out of options and are living with chronic and unrelenting symptoms.

Safe and effective long-term treatments that can help patients live pain-free lives are desperately needed, and yet to date, very few drugs have been approved for clinical use.

Those that have, like elagolix and leuprorelin (aka Orilissa and Lupron), don't work for everyone and cannot be taken for more than two years because of adverse effects.

These drugs can not only lead to significant and potentially irreversible loss of bone density, they can also induce menopausal-like symptoms, such as hot flushes, insomnia, and mood changes.

An experimental drug in the same class, called linzagolix, could one day prove a much better alternative. It is currently being tested by the biopharmaceutical company ObsEva as a potential way to treat endometriosis-associated pain, as well as heavy menstrual bleeding from uterine fibroids.

At the end of 2021, in fact, the results of two, phase-3 clinical trials were enough to convince the United States Federal Drug Advisory (FDA) to review linzagolix as a treatment for uterine fibroids.

It might not be long until officials also consider the drug as a treatment for people with endometriosis.

ObsEva has recently announced "topline" results when using linzagolix to treat women with moderate-to-severe endometriosis-associated pain. The findings from their phase-3 clinical trial have not yet been peer-reviewed, so they need to be taken with a grain of salt. But preliminary results are encouraging – hopefully we'll have more details soon.

Two different daily doses of linzagolix were tested in the trial, including a 200 mg dose and a 75 mg dose.

With the higher dose, patients were also given an "add-back" hormonal therapy, as linzagolix works on the brain to reduce estrogen production in the ovaries.

Endometriosis occurs when tissue similar to the uterus grows elsewhere in the body, where it then responds to hormones, including estrogen, as it would on the inside of the uterus, thickening and bleeding with the menstrual cycle.

This can be associated with a significant amount of pain and not only during menstruation.

Compared to a placebo, both doses of linzagolix resulted in a significant reduction in severe and frequent menstrual cramps, menstrual-related constipation (known as dyschezia), and overall pelvic pain after three months.

At six months, improvements continued. Even better, side effects were limited.

In 2019, during phase 2b clinical trials, hot flushes were the most common adverse outcome of taking linzagolix, impacting about 20 percent of people on the low dose and nearly half of those on the high dose.

Even better, during these trials, low-dose linzagolix showed "no clinically significant impact on bone mineral density", while the high-dose only showed minimal loss.

"While there have been recent advances in non-surgical endometriosis treatment, there is still a critical need for therapeutic options for women who suffer from this chronic condition," says Hugh Taylor, an endometriosis researcher at Yale University who is leading the clinical trials.

"Once daily linzagolix 200 mg with add-back therapy demonstrated excellent efficacy along with minimal changes in bone mineral density, suggesting this dose may be used for long-term treatment."

While both doses of the drug are reported as being significantly and clinically effective, researchers at ObsEva say the low dose is being tested as an option for patients who cannot or do not wish to take hormones with add-back therapy.

The company also intends to explore a higher dose option of linzagolix that does not include add-back hormonal therapy for the same reasons.

The drug may not appeal to everyone with endometriosis, but it is promising that drug researchers and pharmaceutical companies have finally begun to take gynecological pain seriously. The more treatment choices we can give people with incurable conditions, the better chance they have of finding what works for them.