CLINICAL TRIALS PROFILE FOR ESTROGENS, ESTERIFIED

All Clinical Trials for ESTROGENS, ESTERIFIED

Trial ID	Title	Status	Sponsor	Phase	Start Date	Summary
NCT00141544 ↗	The Efficacy of ESTRATEST® Tablets in Relieving Menopausal Symptoms in Estrogenized, Non-Hysterectomized Postmenopausal Women	Terminated	Solvay Pharmaceuticals	Phase 2	2004-07-01	To determine whether treatment with ESTRATEST® Tablets is superior to treatment with esterified estrogens tablets
NCT00141557 ↗	The Efficacy of ESTRATEST® Tablets in Relieving Menopausal Symptoms in Estrogenized, Hysterectomized Postmenopausal Women	Terminated	Solvay Pharmaceuticals	Phase 2	2004-07-01	To determine whether treatment with ESTRATEST® Tablets is superior to treatment with esterified estrogens tablets
NCT00141570 ↗	Study of the Efficacy of ESTRATEST® H.S. Tablets in Relieving Menopausal Symptoms in Estrogenized Postmenopausal Women	Completed	Solvay Pharmaceuticals	Phase 2	2004-06-01	To determine whether treatment with ESTRATEST® H.S. Tablets is superior to treatment with esterified estrogens tablets
NCT00160342 ↗	Comparison of Estrogen and Methyltestosterone Combination Treatments for Postmenopausal Hot Flushes	Completed	Solvay Pharmaceuticals	Phase 2	2005-06-01	This is a research study to evaluate the effectiveness, safety and side effects of several dose levels of esterified estrogens (EE) and methyltestosterone (MT) given individually and in combination compared to a placebo (a tablet with no active drug in it) as a possible treatment for vasomotor symptoms (such as hot flushes and flushing) of menopause. EE and testosterone are two hormones which are typically deficient in menopausal women
NCT00357006 ↗	A Definitive Estrogen Patch Study (ADEPT)	Completed	Stanley Medical Research Institute	Phase 2	2006-07-01	OBJECTIVE: To test the use of adjunctive estrogen in a 8 week, three-arm, double-blind, placebo-controlled study in the treatment of psychotic symptoms in women with schizophrenia. HYPOTHESIS: That women receiving adjunctive estrogen will demonstrate significantly greater improvements in the symptoms of schizophrenia than women receiving adjunctive placebo. STUDY POPULATION: 180 women will be recruited over a three-year period across three sites. Participant will be of potential child-bearing age (Pre-menopausal and Post-menarche) with a current diagnosis of Schizophrenia, Schizophreniform Disorder, or Schizoaffective Disorder (not in manic phase)according to the Mini International Neuropsychiatric Interview (MINI). STUDY MEDICATION: Estradiol. One third of the participants (n=60) will be randomised to receive adjunctive 100mcg Estradiol; one third of the participants (n=60) will be randomised to receive adjunctive 200mcg Estradiol n=60; and, one third of the participants (n=60) will be randomised to receive adjunctive placebo n=60). All patches will be covered with identical adhesive contact to ensure the "blind" is maintained. STUDY EVALUATIONS: Data will be collected over a two-month period for each participant. Visits will be performed at baseline, and then at weekly or fortnightly intervals. A total of six visits will be completed for each participant. The following evaluations will be performed: i) Inclusion/exclusion checklist. (Baseline visit only) ii) Informed consent. (Baseline visit only) iii)psychiatric evaluation to determine diagnosis. (Baseline visit only) iv) General clinical evaluation including medical history, current conditions and a non-invasive physical examination, body weight, vital signs. (Baseline and endpoint visits) v) Medication history. (Baseline and evaluation visits) vi) Demographics. (Baseline visits only) vii) The primary outcome measures will be the Positive and Negative Syndrome Scale (PANSS), which will be taken at weeks 1, 2, 4 and 8 of the trial. Cognitive testing will take place at baseline and 8 weeks. Side effects will be assessed at weeks 1, 2, 4, 6, and 8 to measure changes in subject's reported side effects during the trial. viii) Laboratory tests including; Serum levels of mood stabiliser, LH, FSH, Estrogen, Progesterone, Prolactin, DHEA,Testosterone and(Baseline and evaluation visits).

Clinical Trial Conditions for ESTROGENS, ESTERIFIED

Condition Name

Condition Name for ESTROGENS, ESTERIFIED
Intervention	Trials
Menopause	3
Hot Flushes, Menopause, Postmenopause	1
Schizoaffective Disorder	1
Schizophrenia	1

Condition MeSH

Condition MeSH for ESTROGENS, ESTERIFIED
Intervention	Trials
Schizophrenia	1
Psychotic Disorders	1
Disease	1
Hot Flashes	1

Clinical Trial Locations for ESTROGENS, ESTERIFIED

Trials by Country

Trials by Country for ESTROGENS, ESTERIFIED
Location	Trials
United States	118
Canada	5
Russian Federation	1
Australia	1

Trials by US State

Trials by US State for ESTROGENS, ESTERIFIED
Location	Trials
Washington	4
Virginia	4
Utah	4
Texas	4
Tennessee	4

Clinical Trial Progress for ESTROGENS, ESTERIFIED

Clinical Trial Phase

Clinical Trial Phase for ESTROGENS, ESTERIFIED
Clinical Trial Phase	Trials
Phase 2	5

Clinical Trial Status

Clinical Trial Status for ESTROGENS, ESTERIFIED
Clinical Trial Phase	Trials
Completed	3
Terminated	2

Clinical Trial Sponsors for ESTROGENS, ESTERIFIED

Sponsor Name

Sponsor Name for ESTROGENS, ESTERIFIED
Sponsor	Trials
Solvay Pharmaceuticals	4
Stanley Medical Research Institute	1
The Alfred	1

Sponsor Type

Sponsor Type for ESTROGENS, ESTERIFIED
Sponsor	Trials
Industry	4
Other	2

Esterified Estrogens Clinical Trials, Market Analysis, Patent Status and Forecast

Last updated: July 31, 2026

Esterified estrogens are legacy oral estrogen products used primarily for menopausal vasomotor symptoms and vulvar or vaginal atrophy. The product class has limited current clinical-development activity, no visible late-stage pipeline, and a fragmented generic market. Commercial prospects are constrained by competition from estradiol, conjugated estrogens, transdermal estrogen systems, and nonhormonal therapies.

The principal market opportunity is replacement prescribing for menopausal hormone therapy rather than new product development. Patent-based barriers are limited because the core esterified-estrogen compositions and conventional tablet technologies are old. Regulatory and commercial risk centers on product availability, manufacturing economics, estrogen safety labeling, and substitution by newer dosage forms.

What are esterified estrogens and how are they used?

Esterified estrogens are a mixture of estrogenic substances, primarily estrone sulfate and equilin sulfate, derived from natural or synthetic estrogen sources. They are supplied as oral tablets in several strengths, historically including 0.3 mg, 0.625 mg, 1.25 mg, and 2.5 mg.

The product class has been used for:

• Moderate to severe vasomotor symptoms associated with menopause.
• Vulvar and vaginal atrophy.
• Hypoestrogenism caused by hypogonadism, castration, or primary ovarian failure.
• Palliative treatment of selected advanced breast or prostate cancer indications under historical labeling.

Systemic estrogen therapy carries boxed warnings relating to endometrial cancer, cardiovascular events, breast cancer, and probable dementia in postmenopausal women. Women with an intact uterus generally require an appropriate progestogen when systemic estrogen is prescribed, because unopposed estrogen increases endometrial hyperplasia and cancer risk. The product label also identifies contraindications including breast or estrogen-dependent cancer, active or prior thromboembolic disease, stroke, myocardial infarction, liver dysfunction, and undiagnosed genital bleeding. (U.S. Food and Drug Administration [FDA], n.d.-a)

What is the FDA regulatory status of esterified estrogens?

Esterified estrogens remain an established active pharmaceutical ingredient and dosage-form concept, but commercial status varies by manufacturer and National Drug Code.

The historical reference product is Menest, an oral esterified-estrogens tablet. Menest was marketed in multiple strengths and was associated with the legacy NDA 016954. Current commercial availability has been inconsistent, and some historical products have been discontinued or are no longer actively marketed.

FDA regulatory status should be assessed at the individual product level rather than by active ingredient alone:

Regulatory element	Status
Active ingredient	Esterified estrogens
Primary dosage form	Immediate-release oral tablet
Historical reference brand	Menest
Main approval pathway for current products	ANDA-based generic approval or legacy NDA status
FDA-approved indication	Menopausal symptoms, vulvar or vaginal atrophy, selected hypoestrogenic conditions
Current development profile	No evident active innovation program around the legacy oral product
Main regulatory constraints	Class estrogen warnings, labeling, bioequivalence, manufacturing controls

The FDA’s Orange Book should be checked by product name, active ingredient, and application number because listed products can change through discontinuation, withdrawal, or sponsor updates. Orange Book listing status does not by itself establish current commercial supply. (FDA, n.d.-b)

What clinical trials are evaluating esterified estrogens?

There is no identifiable active late-stage clinical program centered on esterified estrogens as a novel therapy. Contemporary menopause trials generally evaluate estradiol, conjugated estrogens, bazedoxifene-conjugated estrogens, tissue-selective estrogen complexes, or nonhormonal agents rather than legacy esterified-estrogen tablets.

A registry review of ClinicalTrials.gov shows that esterified estrogens have primarily appeared in older comparative, pharmacokinetic, or hormone-therapy studies. Current trial activity is concentrated in the following areas:

Clinical area	Relevance to esterified estrogens	Development outlook
Menopausal vasomotor symptoms	Historical indication	Low likelihood of new pivotal trials
Vulvovaginal atrophy	Oral systemic estrogen is less targeted than local therapy	Limited
Cardiovascular prevention	Not a viable development strategy after major hormone-therapy findings	Very limited
Breast cancer prevention	Risk-benefit profile does not support broad development	Limited
Pharmacokinetics and bioequivalence	Relevant for generic approvals	Possible, sponsor-specific
Lower-dose or novel delivery systems	More likely to use estradiol or other estrogen products	Competitive threat to esterified estrogens

The Women’s Health Initiative found that menopausal hormone therapy has clinically important risk-benefit tradeoffs, including increased risks that vary by estrogen-only versus estrogen-plus-progestin therapy and by patient characteristics. Those findings reduced the likelihood that an older systemic estrogen product would support a broad preventive indication. (Women’s Health Initiative Steering Committee, 2004; Rossouw et al., 2002)

What is the current clinical evidence for esterified estrogens?

The clinical rationale for esterified estrogens is established, but the evidence base is older than the evidence supporting many newer delivery systems. The product’s current use depends on symptom control at the lowest effective dose for the shortest duration consistent with treatment objectives.

Key evidence considerations include:

1. Systemic estrogen is effective for menopausal vasomotor symptoms.
2. Oral estrogen increases hepatic exposure compared with transdermal delivery.
3. Estrogen-only therapy is generally limited to women without a uterus, subject to individualized risk assessment.
4. Estrogen plus progestogen is used when endometrial protection is required.
5. Local vaginal estrogen is generally preferred when symptoms are limited to genitourinary tissues.
6. Long-term preventive use for cardiovascular disease is not supported.

The North American Menopause Society states that hormone therapy remains an effective treatment for vasomotor symptoms and genitourinary syndrome of menopause, but treatment must be individualized according to age, time since menopause, indication, dose, route, duration, and medical history. (The North American Menopause Society, 2022)

How large is the esterified-estrogens market?

Esterified estrogens occupy a narrow segment of the broader menopausal hormone-therapy market. Public company reporting rarely discloses esterified-estrogen revenue separately, and syndicated market reports generally combine the product with broader estrogen or hormone-replacement categories.

The commercial market has four characteristics:

• Low differentiation among oral systemic estrogen products.
• Generic pricing pressure.
• Limited prescriber preference for esterified estrogens over estradiol.
• Supply sensitivity because relatively low-volume products may have limited manufacturing redundancy.

The broader menopausal hormone-therapy market includes oral estradiol, transdermal patches, gels, sprays, vaginal estrogen, estrogen-progestin combinations, and selective estrogen receptor modulators. Esterified estrogens compete most directly with oral estradiol and conjugated estrogens.

Market segmentation

Segment	Competitive position of esterified estrogens
Oral systemic estrogen	Established but secondary
Transdermal estrogen	Less competitive because of route and pharmacokinetic advantages
Vaginal estrogen	Poor substitute for patients needing local therapy only
Estrogen-progestin combinations	Competes only when a complete regimen is prescribed
Nonhormonal vasomotor treatments	Increasing alternative for patients avoiding hormone therapy
Compounded hormone products	Alternative channel, though quality and regulatory controls differ

The addressable market is therefore determined by continued use of oral systemic hormone therapy, not by expansion of the total menopause-treatment market.

What is the market projection for esterified estrogens?

The base-case outlook is a low-growth or declining market in unit terms, with periodic price increases caused by limited supply rather than demand expansion. A meaningful rebound would require a new sponsor, improved availability, or a differentiated formulation.

Scenario	Expected market direction	Main drivers
Base case	Flat to declining volume	Generic substitution, estradiol competition, aging product profile
Upside case	Modest recovery	Reliable supply, new generic entrant, targeted menopause prescribing
Downside case	Steep contraction	Product discontinuation, manufacturing interruption, substitution by estradiol or transdermal products

Revenue may rise temporarily even as units decline if a supplier gains market share during a shortage or if the remaining manufacturer increases prices. That would not indicate durable demand expansion.

The stronger commercial opportunity is in adjacent products:

• Low-dose transdermal estradiol.
• Vaginal estrogen inserts, creams, and rings.
• Combined estrogen-progestin products.
• Nonhormonal therapies for vasomotor symptoms.
• Simplified regimens with improved adherence.
• Products with lower systemic exposure.

What patents protect esterified estrogens?

The core composition of matter for esterified estrogens is long expired. Conventional oral-tablet patents associated with historical products are also expected to be expired or commercially immaterial.

The relevant intellectual-property categories are:

Patent category	Commercial relevance
Esterified estrogen composition	Core protection is expired
Oral tablet formulation	Generally old and unlikely to block generic entry
Dosage regimen	Potentially limited by prior art and labeling scope
Combination with progestogen	More relevant to combination products than esterified estrogens alone
Modified-release formulation	Potential opportunity if a new formulation is developed
Manufacturing or purification	Could create process barriers, but usually does not block ordinary generic tablets
Device or delivery system	More relevant to patches, rings, gels, and inserts

A current freedom-to-operate analysis should focus on active patents covering a specific formulation, process, combination, or delivery system. The legacy active ingredient itself is not a strong patent barrier.

How many patents cover esterified estrogens?

No meaningful active composition-of-matter patent estate is expected to cover conventional esterified-estrogen tablets in the United States. Any relevant surviving claims would more likely relate to a particular formulation, manufacturing process, combination, or method of treatment.

Patent risk should therefore be separated into three layers:

1. Core drug risk: low.
2. Product-specific formulation risk: potentially moderate if a sponsor develops a new release profile or combination.
3. Manufacturing risk: sponsor-specific and dependent on process claims, trade secrets, and qualified suppliers.

Patent databases should be searched using the active ingredient names, historical brand names, assignees, and related estrogen terms. A search limited to "esterified estrogens" can miss patents drafted around individual sulfate components, hormone combinations, dosage regimens, or delivery technologies.

Are there Paragraph IV challenges to esterified estrogens?

Paragraph IV litigation risk appears limited for the legacy oral product. Generic entry is more likely to occur through routine ANDA development, product discontinuation, or supply substitution than through a high-value patent challenge.

A Paragraph IV certification is relevant only when an ANDA applicant identifies an Orange Book-listed patent and certifies that the patent is invalid, unenforceable, or will not be infringed. If no active listed patents remain for the relevant reference product, the principal entry pathway may be Paragraph III or a certification that no patent information is listed, depending on the product and FDA records. (FDA, n.d.-b; FDA, n.d.-c)

Entry issue	Assessment
Core composition patent	Low risk
Active formulation patent	Product-specific
Method-of-use patent	Limited for broad legacy indications
Paragraph IV litigation	Low apparent exposure
180-day exclusivity	Depends on ANDA and first-filer status
Approval risk	Primarily CMC, bioequivalence, and supply related

What generic entry risks exist for esterified estrogens?

Generic entry can occur without a major patent event. The relevant risks are:

• An ANDA applicant securing approval and displacing an incumbent.
• A manufacturer exiting because of low margins.
• A manufacturing interruption creating temporary shortages.
• Pharmacies substituting oral estradiol.
• Payers placing esterified estrogens on unfavorable formulary tiers.
• Physicians switching patients to transdermal or vaginal products.
• New safety-labeling requirements affecting systemic estrogen products.

For a potential entrant, the main barriers are commercial scale, reliable API sourcing, tablet uniformity, dissolution performance, bioequivalence, pharmacovigilance, and reimbursement. Patent protection is unlikely to provide a durable moat.

What is the Orange Book status of esterified estrogens?

Orange Book status must be reviewed at the NDA and product level. Historical reference products may remain in FDA records even when the product is no longer actively marketed. A discontinued product can still have regulatory relevance, but its listing does not guarantee current supply or exclusivity.

The most important Orange Book questions are:

• Whether an active reference listed drug remains available.
• Whether any patents are listed against the relevant NDA.
• Whether FDA has identified a therapeutically equivalent generic.
• Whether the reference product has been withdrawn for safety or merely discontinued commercially.
• Whether the dosage strength and formulation match the proposed generic product.

FDA’s Approved Drug Products with Therapeutic Equivalence Evaluations is the controlling source for current Orange Book determinations. (FDA, n.d.-b)

What patent litigation affects esterified estrogens?

No major current patent dispute is central to the esterified-estrogen market. Historical estrogen litigation has generally involved other products, including conjugated estrogens, combination hormone therapies, transdermal systems, and branded menopause products.

The absence of major litigation changes the competitive focus. Commercial outcomes are more likely to depend on:

• Supply continuity.
• FDA manufacturing compliance.
• API availability.
• Generic pricing.
• Prescriber familiarity.
• Reimbursement.
• Safety communications.

A sponsor entering this segment should not assume that an absence of litigation means an absence of risk. Manufacturing and regulatory execution are more important than patent enforcement.

How does esterified estrogen compare with estradiol and conjugated estrogens?

Attribute	Esterified estrogens	Estradiol	Conjugated estrogens
Main use	Systemic menopausal therapy	Systemic and local therapy	Systemic and local therapy
Oral availability	Yes	Yes	Yes
Transdermal availability	No conventional legacy esterified-estrogen equivalent	Strong	Limited relative to estradiol
Vaginal products	Limited	Broad	Available
Generic competition	High or fragmented	High	Present but product-dependent
Patent strength	Low for legacy tablets	Varies by formulation	Varies by product and formulation
Clinical positioning	Established but dated	Broad and flexible	Branded and formulation-specific
Commercial growth	Limited	Stronger in differentiated routes	Product-specific

Estradiol has a broader delivery platform and is better positioned for new product development. Conjugated estrogens retain brand recognition and differentiated products but face their own generic and regulatory pressures. Esterified estrogens are most exposed to substitution because they lack a strong current delivery-system franchise.

What licensing deals and partnerships involve esterified estrogens?

There is no prominent current licensing transaction associated specifically with conventional esterified-estrogen tablets. Historical ownership and commercialization arrangements may exist around legacy brands, but they do not create a visible innovation platform.

Potential transaction value would be based on:

• An approved product with reliable supply.
• An ANDA with limited competition.
• Rights to a differentiated low-dose formulation.
• Manufacturing capacity for a scarce product.
• A combination product with a progestogen.
• Regulatory rights in markets where estrogen therapy remains commercially active.

A transaction involving only legacy esterified-estrogen tablets would likely be valued as a product-supply or portfolio transaction rather than as a patent-backed innovation deal.

What geographic markets offer opportunity?

The United States remains the most structured market because of FDA approval, Orange Book substitution, and established menopausal hormone-therapy prescribing. Europe and other developed markets often favor estradiol-based products and transdermal systems, reducing the relative position of esterified estrogens.

Geographic opportunity is strongest where:

• Oral estrogen products remain reimbursed.
• Generic substitution is established.
• A local manufacturer has API and tablet capacity.
• Menopausal hormone therapy is underpenetrated.
• Regulatory pathways recognize established products efficiently.

Market access must account for country-specific decisions on estrogen nomenclature, approved indications, required progestogen use, pharmacovigilance, and reimbursement. A U.S. approval does not establish automatic commercial viability elsewhere.

How strong is the esterified-estrogen commercial and patent estate?

The overall estate is weak as an innovation platform but potentially useful as a niche generic product.

Factor	Rating	Rationale
Composition-of-matter protection	Low	Legacy active ingredient
Formulation protection	Low for conventional tablets
Clinical differentiation	Low to moderate	Established efficacy, limited novelty
Regulatory familiarity	Moderate to high	Long history of use
Generic-entry resistance	Low	Limited apparent patent barriers
Supply-chain defensibility	Moderate	Depends on API and manufacturing access
Growth potential	Low	Mature product class
Litigation exposure	Low apparent current exposure	Few visible patent disputes
Commercial execution risk	Moderate to high	Volume, supply, and margin pressure

Key Takeaways

• Esterified estrogens are mature systemic estrogen products with limited current clinical-development activity.
• No major late-stage trial program or novel mechanism is associated with the legacy product class.
• The core patent estate for conventional tablets is effectively exhausted as a commercial barrier.
• Paragraph IV and patent-litigation exposure appear limited compared with newer branded hormone products.
• The principal risks are supply interruption, generic pricing, formulation substitution, and regulatory compliance.
• Estradiol, particularly transdermal and vaginal formulations, is the strongest competitive substitute.
• Market growth is unlikely without a differentiated formulation, reliable supply advantage, or new combination product.
• Revenue exposure is concentrated in niche generic sales rather than a high-growth branded franchise.

FAQs

Is esterified estrogen the same as conjugated estrogen?

No. Esterified estrogens and conjugated estrogens are different estrogen mixtures with distinct composition, manufacturing history, labeling, and product portfolios.

Is Menest still available?

Availability depends on the specific strength, manufacturer, distributor, and current FDA marketing records. Historical Menest records do not establish continuous commercial supply.

Does esterified estrogen have a generic version?

Generic esterified-estrogen tablets have been marketed historically, but current availability must be confirmed by strength and manufacturer in FDA product records.

Are esterified estrogens used in clinical trials for menopause?

They have appeared in historical hormone-therapy research, but current menopause trials more commonly evaluate estradiol, conjugated estrogens, nonhormonal agents, and newer delivery systems.

Can esterified-estrogen tablets support a new patent strategy?

A conventional tablet is unlikely to support strong new patent protection. A viable strategy would require a differentiated formulation, delivery system, combination, manufacturing process, or clinically meaningful dosing regimen.

References

1. Food and Drug Administration. (n.d.-a). Menest: Esterified estrogens tablets prescribing information. U.S. Department of Health and Human Services.

2. Food and Drug Administration. (n.d.-b). Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.

3. Food and Drug Administration. (n.d.-c). Drugs@FDA: FDA-approved drugs. U.S. Department of Health and Human Services.

4. Rossouw, J. E., Anderson, G. L., Prentice, R. L., LaCroix, A. Z., Kooperberg, C., Stefanick, M. L., Jackson, R. D., Beresford, S. A. A., Howard, B. V., Johnson, K. C., Kotchen, J. M., & Ockene, J. (2002). Risks and benefits of estrogen plus progestin in healthy postmenopausal women: Principal results from the Women’s Health Initiative randomized controlled trial. JAMA, 288(3), 321-333.

5. The North American Menopause Society. (2022). The 2022 hormone therapy position statement of The North American Menopause Society. Menopause, 29(7), 767-794.

6. Women’s Health Initiative Steering Committee. (2004). Effects of conjugated equine estrogen in postmenopausal women with hysterectomy: The Women’s Health Initiative randomized controlled trial. JAMA, 291(14), 1701-1712.