How Does Estradiol/Norethindrone/Relugolix Work? Mechanism of Action Explained in Plain English

How Does Estradiol/Norethindrone/Relugolix Work?

Estradiol/Norethindrone/Relugolix (Myfembree) works by turning down your body's estrogen production to shrink fibroids and reduce endometriosis tissue, while adding back just enough hormone to protect your bones and prevent severe menopause-like symptoms.

That's the one-sentence version. But if you want to understand why this medication works — and why it was designed with three ingredients instead of one — here's the full explanation in plain English.

What It Does in Your Body

To understand Myfembree, it helps to think of your hormonal system like a thermostat. Your brain (specifically the hypothalamus and pituitary gland) acts as the thermostat, and estrogen is the temperature. Here's how each ingredient plays its role:

Relugolix: The Thermostat Blocker

Relugolix is the primary active ingredient and a GnRH receptor antagonist. Here's what that means:

Your brain naturally releases a hormone called GnRH (gonadotropin-releasing hormone) that tells your pituitary gland to produce LH (luteinizing hormone) and FSH (follicle-stimulating hormone). These hormones then signal your ovaries to produce estrogen and progesterone.

Relugolix blocks the GnRH receptors in your pituitary gland — essentially covering the thermostat so it can't receive the signal. Without that signal, your pituitary stops telling your ovaries to make as much estrogen. Estrogen levels drop significantly.

This matters because uterine fibroids and endometriosis tissue are fueled by estrogen. When estrogen drops:

• Fibroids shrink and cause less bleeding
• Endometriosis tissue becomes less active, reducing pain and inflammation

Think of it like cutting the fuel supply to a fire — the fire doesn't go out completely, but it burns much less intensely.

Estradiol + Norethindrone Acetate: The Safety Net

If Relugolix suppresses estrogen, why add estrogen (Estradiol) and a progestin (Norethindrone Acetate) back in?

Because too little estrogen causes problems too. Without any estrogen, you'd experience significant bone loss, severe hot flashes, vaginal dryness, and other symptoms of menopause. Older medications like Lupron (Leuprolide) suppressed estrogen without any add-back, which limited how long patients could safely use them.

The add-back therapy in Myfembree is carefully dosed:

• Estradiol 1 mg — Provides just enough estrogen to slow bone mineral density loss and reduce vasomotor symptoms (hot flashes, night sweats)
• Norethindrone Acetate 0.5 mg — A progestin that protects the uterine lining from the effects of the added estrogen (unopposed estrogen can increase the risk of endometrial hyperplasia)

The result is a Goldilocks zone: estrogen levels low enough to treat fibroids and endometriosis, but high enough to keep your bones and body from suffering the worst consequences of estrogen deprivation.

How Long Does It Take to Work?

Most women begin to notice changes within the first few weeks to months of starting treatment:

• Menstrual bleeding reduction: Many women see a significant decrease in heavy bleeding within the first 1 to 2 menstrual cycles (4 to 8 weeks)
• Endometriosis pain relief: Pain improvement can begin within the first month, though maximum benefit may take 2 to 3 months
• Fibroid size reduction: Fibroids may begin to shrink over several months of treatment, though the primary goal is symptom control (reduced bleeding) rather than eliminating the fibroids entirely

Because of potential bone density effects, treatment is limited to up to 24 months. Your doctor will monitor your response and bone health throughout treatment.

How Long Does It Last?

Estradiol/Norethindrone/Relugolix works while you're taking it. Once you stop the medication:

• Hormones recover quickly — Unlike injectable GnRH agonists like Lupron, Relugolix is an oral medication taken daily, so its effects wear off relatively fast. Hormone levels typically begin returning to baseline within days to weeks after stopping.
• Periods return — Most women see their menstrual periods return within a few weeks to a couple of months after discontinuation.
• Fibroids may regrow — Since the medication treats symptoms rather than permanently removing fibroids, they can grow back once estrogen levels return to normal. Some women may need to discuss surgical options or alternative treatments after stopping.
• Bone density — Any bone mineral density lost during treatment may not be fully recovered after stopping, which is why the 24-month limit and periodic DXA scans are important.

What Makes It Different from Similar Medications?

Several other medications target the same hormonal pathway, but Myfembree has some distinct advantages:

Compared to Lupron (Leuprolide)

• Lupron is an injectable GnRH agonist — it initially causes a hormonal "flare" (temporary worsening of symptoms) before suppression kicks in. Myfembree (a GnRH antagonist) starts suppressing immediately with no flare.
• Lupron requires monthly or every-3-month injections. Myfembree is a daily oral tablet.
• Lupron doesn't include built-in add-back therapy, so doctors often need to prescribe separate hormones alongside it.

Compared to Oriahnn (Elagolix/Estradiol/Norethindrone Acetate)

• Oriahnn is the closest competitor — also a GnRH antagonist with hormonal add-back. However, Oriahnn requires twice-daily dosing with different morning and evening capsules, while Myfembree is one tablet, once daily.
• Oriahnn is FDA-approved only for uterine fibroids, while Myfembree is approved for both fibroids and endometriosis.

Compared to Orilissa (Elagolix)

• Orilissa is a GnRH antagonist without built-in add-back therapy. It's approved for endometriosis pain but requires separate add-back therapy prescriptions if needed.
• Myfembree's all-in-one approach is simpler and ensures patients get the add-back therapy they need.

Compared to Hormonal IUDs (Mirena)

• Hormonal IUDs like Mirena are often used as first-line treatment for heavy fibroid bleeding. They don't shrink fibroids — they reduce bleeding locally. Myfembree actually shrinks fibroids by lowering systemic estrogen levels.
• IUDs can last 5 to 8 years; Myfembree is limited to 24 months.

Final Thoughts

Estradiol/Norethindrone/Relugolix is a well-designed combination that balances effectiveness with tolerability. By blocking estrogen production where it counts while adding back just enough hormone to protect your health, it achieves something older treatments couldn't: meaningful symptom relief without forcing you into full-blown menopause.

Understanding how your medication works can help you stick with treatment and recognize what's normal versus what needs attention. For more on what to expect, check out our guides on side effects and drug interactions.

Find Estradiol/Norethindrone/Relugolix in stock near you with Medfinder →