STILBESTROL Drug Patent Profile

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Which patents cover Stilbestrol, and when can generic versions of Stilbestrol launch?

Stilbestrol is a drug marketed by Bristol Myers Squibb and Tablicaps and is included in seven NDAs.

The generic ingredient in STILBESTROL is diethylstilbestrol. There is one drug master file entry for this compound. Additional details are available on the diethylstilbestrol profile page.

Summary for STILBESTROL

US Patents:	0
Applicants:	2
NDAs:	7
Raw Ingredient (Bulk) Api Vendors:	3
Patent Applications:	18
DailyMed Link:	STILBESTROL at DailyMed

US Patents and Regulatory Information for STILBESTROL

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Bristol Myers Squibb	STILBESTROL	diethylstilbestrol	INJECTABLE;INJECTION	004056-003	Approved Prior to Jan 1, 1982		DISCN	No	No
Tablicaps	STILBESTROL	diethylstilbestrol	TABLET, DELAYED RELEASE;ORAL	083003-001	Approved Prior to Jan 1, 1982		DISCN	No	No
Bristol Myers Squibb	STILBESTROL	diethylstilbestrol	INJECTABLE;INJECTION	004056-006	Approved Prior to Jan 1, 1982		DISCN	No	No
Tablicaps	STILBESTROL	diethylstilbestrol	TABLET;ORAL	083006-001	Approved Prior to Jan 1, 1982		DISCN	No	No
Tablicaps	STILBESTROL	diethylstilbestrol	TABLET, DELAYED RELEASE;ORAL	083005-001	Approved Prior to Jan 1, 1982		DISCN	No	No
Bristol Myers Squibb	STILBESTROL	diethylstilbestrol	INJECTABLE;INJECTION	004056-004	Approved Prior to Jan 1, 1982		DISCN	No	No
Bristol Myers Squibb	STILBESTROL	diethylstilbestrol	INJECTABLE;INJECTION	004056-005	Approved Prior to Jan 1, 1982		DISCN	No	No

Stilbestrol Market Dynamics, Financial Trajectory, and Patent Status

Last updated: August 31, 2026

Stilbestrol, generally referring to diethylstilbestrol (DES), has no meaningful current pharmaceutical market in the United States. Its commercial trajectory moved from broad estrogen use in the mid-20th century to regulatory withdrawal, litigation exposure, sharply reduced demand, and near-total loss of branded commercial value. No active patent estate supports market exclusivity, and no material standalone revenue is publicly reported for Stilbestrol or DES.

What is Stilbestrol and how was it used?

Stilbestrol is a historical trade name for diethylstilbestrol, a synthetic nonsteroidal estrogen. DES was used in several settings:

• Prevention of miscarriage and pregnancy complications
• Hormone replacement and estrogen-deficiency treatment
• Treatment of prostate cancer
• Treatment of breast cancer in selected postmenopausal patients
• Historical veterinary applications

DES became commercially important after its introduction in the 1940s. Its use during pregnancy declined after studies linked prenatal exposure to clear-cell adenocarcinoma and reproductive abnormalities in exposed offspring. The National Cancer Institute identifies DES exposure in utero as a cause of increased risk for clear-cell adenocarcinoma of the vagina and cervix, structural reproductive abnormalities, infertility, and pregnancy complications (National Cancer Institute, n.d.).

The drug is also known as diethylstilbestrol, stilboestrol, and DES. Product names varied by jurisdiction and manufacturer.

When did Stilbestrol lose commercial exclusivity?

Stilbestrol lost meaningful exclusivity decades ago. DES was discovered and commercialized before the modern U.S. patent and regulatory framework created significant long-duration pharmaceutical exclusivity. Any original composition or manufacturing patents would have expired many decades ago.

Commercial milestone	Approximate period	Market effect
DES synthesized and introduced	1930s-1940s	Commercial estrogen market established
Broad obstetric use	1940s-1960s	High-volume demand across multiple indications
Evidence of prenatal harm emerges	1970s	Pregnancy use collapses
FDA warning against use in pregnancy	1971	Major U.S. indication removed
Litigation and compensation exposure	1970s onward	Manufacturer risk increases
Decline in oncology and hormone use	1980s-1990s	Demand becomes limited and specialized
Modern period	2000s-present	No material branded market; limited legacy or compounded use

The FDA stated in 1971 that DES should not be used during pregnancy because available evidence showed that its use did not prevent miscarriage and raised safety concerns. The regulatory action eliminated the largest historical market for the drug (U.S. Food and Drug Administration, 1971).

What is the FDA regulatory status of Stilbestrol?

Stilbestrol does not have a meaningful current U.S. commercial approval profile.

DES is not an active mainstream prescription product in the United States. It is absent from current therapeutic practice for pregnancy prevention and is not an accepted treatment for routine obstetric use. Historical FDA-approved uses may appear in older regulatory records, but those records do not establish a current commercial market.

The modern U.S. status can be summarized as follows:

Regulatory issue	Current assessment
Active U.S. branded product	None of material commercial significance
Current pregnancy indication	No
Current routine obstetric use	No
Active Orange Book commercial listing	No material listing supporting a branded market
New drug exclusivity	None
Orphan-drug exclusivity	None identified
Pediatric exclusivity	None
180-day generic exclusivity dispute	None of current commercial relevance
Biosimilar pathway	Not applicable

The FDA’s withdrawal of pregnancy use was the decisive regulatory event. The agency later recognized that DES had been used for decades in pregnant patients despite a lack of demonstrated benefit and evidence of serious offspring risks (U.S. Food and Drug Administration, 1971).

What patents protect Stilbestrol?

No unexpired composition-of-matter, formulation, method-of-use, or manufacturing patent is known to protect Stilbestrol in the United States.

Composition patents

Any composition patents covering diethylstilbestrol originated in the early development era of synthetic estrogens. Those rights expired long before the current patent term framework became relevant to modern pharmaceutical products.

Formulation patents

Historical tablets, capsules, injectable products, and other dosage forms may have been covered by manufacturing or formulation claims in the past. Those rights are expired. No current commercial formulation patent appears to create market exclusivity.

Method-of-use patents

Historical uses in pregnancy, prostate cancer, breast cancer, and estrogen replacement are either expired, medically obsolete, or no longer commercially relevant. No current method-of-use patent creates a practical barrier to compounding or generic manufacture.

Manufacturing patents

Manufacturing processes for DES are established chemical processes. Any historical process patents have expired. Current barriers are more likely to arise from regulatory compliance, quality control, toxicological handling, demand concentration, and supplier economics than from enforceable patent rights.

Patent category	Current protection
Active ingredient	No meaningful unexpired protection
Salt or polymorph	No commercially relevant protection identified
Tablet or capsule formulation	No meaningful unexpired protection
Injectable formulation	No meaningful unexpired protection
Method of use	No active commercially relevant exclusivity
Manufacturing process	No active patent barrier of material significance
Device or delivery system	Not commercially relevant

How many patents cover Stilbestrol today?

No meaningful active patent estate covers Stilbestrol today. The relevant patent count for commercial planning is effectively zero.

This assessment differs from a historical patent search, which could identify expired patents, foreign filings, process claims, and litigation-related patent documents. Those records do not create current exclusivity or support a premium-priced market.

There is also no patent-based reason for a generic applicant to await a patent expiry date. A prospective manufacturer would face regulatory and commercial questions, not a conventional patent-cliff timetable.

Were there Paragraph IV challenges to Stilbestrol?

No current Paragraph IV challenge has material commercial relevance for Stilbestrol.

A Paragraph IV certification applies when a generic applicant asserts that a listed patent is invalid, unenforceable, or not infringed. Because DES lacks a commercially relevant active Orange Book patent estate, there is no present Paragraph IV contest comparable to those involving high-value branded medicines.

Historical generic competition occurred through ordinary market entry after the relevant rights and approvals expired. The commercial problem today is demand erosion, not patent litigation.

What litigation affected Stilbestrol?

DES generated substantial product-liability litigation, especially after prenatal exposure was associated with cancer and reproductive injury.

Core litigation themes

• Failure-to-warn claims
• Prenatal exposure claims
• Clear-cell adenocarcinoma
• Infertility and reproductive abnormalities
• Difficulties identifying the original manufacturer
• Market-share liability theories
• Long-tail claims by exposed offspring

The litigation materially changed the economics of DES. Manufacturers faced liability linked to products dispensed decades earlier, when records were incomplete and patients often could not identify the original source. Several U.S. courts addressed whether market-share theories could substitute for traditional product identification in DES cases.

These cases did not create a modern patent barrier. They affected manufacturer participation, insurance costs, reserves, reputational exposure, and willingness to maintain commercial supply.

What is the current market size for Stilbestrol?

There is no reliable public estimate of a standalone Stilbestrol market because the product has no material branded sales base and is not tracked as a major commercial pharmaceutical.

The current market is best characterized as fragmented and low-volume:

1. Historical or legacy clinical use in limited jurisdictions
2. Compounded or special-access prescriptions
3. Potential veterinary or research use, subject to local regulation
4. Institutional supply for narrow oncology or endocrine applications
5. Residual international sales under local product names

Public financial databases generally do not report DES revenue as a separate product line. Any sales would likely be embedded in broader generic, hospital, compounding, or specialty pharmaceutical categories.

Financial metric	Current visibility
Global Stilbestrol revenue	Not publicly reported as a distinct category
U.S. branded revenue	No material revenue base identified
Originator revenue	No active originator franchise identified
Generic revenue	Fragmented and undisclosed
Pricing power	Minimal
Reimbursement leverage	Low
Forecast growth	No credible growth case based on ordinary pharmaceutical demand
Revenue concentration	Likely concentrated among specialty suppliers, if any

What is the financial trajectory for Stilbestrol?

Stilbestrol’s financial trajectory is a long-term decline from mass-market estrogen to a low-volume legacy product.

Phase 1: Expansion

During the 1940s through the 1960s, DES benefited from broad prescribing across obstetrics, endocrinology, oncology, and veterinary medicine. The product had wide distribution and multiple indications.

Phase 2: Regulatory contraction

The 1971 FDA warning removed pregnancy use, historically the most important demand driver. Prescribing declined sharply as physicians shifted away from DES and manufacturers faced increasing liability concerns.

Phase 3: Specialty-market persistence

DES retained limited utility in selected oncology and endocrine settings, including certain cases of advanced prostate or breast cancer. These uses were progressively displaced by newer hormonal agents, chemotherapy, androgen-deprivation approaches, aromatase inhibitors, selective estrogen receptor modulators, and other targeted therapies.

Phase 4: Commercial marginalization

The modern product has low volume, weak pricing power, no meaningful exclusivity, and little strategic value for large pharmaceutical companies. Supply economics depend on whether a manufacturer can justify production, quality testing, regulatory maintenance, and liability controls for a small patient population.

Which companies compete with Stilbestrol?

Stilbestrol competes primarily with modern therapeutic classes rather than with another branded DES product.

Historical competitors

• Diethylstilbestrol products from multiple generic manufacturers
• Other synthetic estrogens
• Conjugated estrogens
• Estradiol products
• Ethinyl estradiol products

Modern therapeutic substitutes

For prostate cancer, alternatives include androgen-deprivation therapies, gonadotropin-releasing hormone agonists and antagonists, antiandrogens, and other systemic treatments.

For breast cancer, alternatives include aromatase inhibitors, selective estrogen receptor modulators, selective estrogen receptor degraders, chemotherapy, and targeted therapies.

For hormone replacement, alternatives include estradiol, transdermal estrogen, vaginal estrogen, and non-estrogen treatments where appropriate.

The substitution threat is structurally high because newer products generally have stronger evidence, more standardized dosing, better safety positioning, and active commercial support.

What generic entry risks exist for Stilbestrol?

Patent-driven generic entry risk is negligible because there is no meaningful patent cliff remaining. The more relevant risk is supply discontinuity.

Risks to incumbent suppliers

• Small and declining demand
• Limited manufacturing scale
• Quality-control costs
• Hazardous-compound handling requirements
• Product-liability exposure
• Regulatory maintenance costs
• Competition from compounding pharmacies
• Physician preference for newer alternatives

Risks to prospective entrants

A new manufacturer could face low barriers to intellectual-property entry but poor commercial returns. The business case would depend on confirmed demand, reliable active pharmaceutical ingredient supply, regulatory approval requirements, and the ability to manage liability exposure.

Are there licensing deals for Stilbestrol?

No material current licensing deal is publicly associated with Stilbestrol or diethylstilbestrol.

The original intellectual property is too old to support conventional royalty economics. Any current supply arrangement would more likely involve contract manufacturing, distribution, compounding, or specialty procurement rather than a strategic license covering proprietary technology.

How strong is the Stilbestrol patent estate?

The patent estate is commercially weak to nonexistent.

Strength factor	Assessment
Patent term	Expired
Composition protection	Expired
Formulation protection	Expired or immaterial
Use protection	Expired or clinically obsolete
Manufacturing protection	Expired
Regulatory exclusivity	None of current significance
Litigation leverage	Minimal on patent grounds
Commercial defensibility	Low

The remaining value, if any, lies in manufacturing capability, regulatory know-how, supply reliability, and access to narrow clinical channels. Those are operational assets rather than patent assets.

What geographic markets still use Stilbestrol?

Use is highly jurisdiction-dependent. The United States has no meaningful mainstream market. Limited availability may persist in countries where older oncology or endocrine protocols remain in use, but international demand is not sufficiently visible to support a reliable global market estimate.

The regulatory status must be assessed country by country because:

• Product approvals differ
• Brand names differ
• Prescription controls differ
• Veterinary use may be regulated separately
• Compounding rules vary
• Legacy products may remain registered without significant distribution

A historical foreign registration should not be treated as evidence of active commercial demand.

Key Takeaways

• Stilbestrol generally refers to diethylstilbestrol, a synthetic estrogen.
• The product’s major commercial market disappeared after the FDA warned against use during pregnancy in 1971.
• Prenatal exposure litigation created substantial long-tail liability for manufacturers.
• No meaningful unexpired patent estate protects the active ingredient, formulations, uses, or manufacturing methods.
• There is no current commercially relevant Paragraph IV or biosimilar risk.
• No material standalone revenue or active branded franchise is publicly reported.
• Modern substitutes have displaced DES in oncology, hormone replacement, and other therapeutic areas.
• The current opportunity is limited to fragmented, low-volume supply rather than growth-oriented pharmaceutical commercialization.

Frequently Asked Questions

Is Stilbestrol still prescribed in the United States?

It is not a routine U.S. prescription product. Historical use in pregnancy is obsolete and contraindicated because of documented risks associated with prenatal exposure.

Is diethylstilbestrol the same as Stilbestrol?

Yes. Stilbestrol is a historical trade name commonly used for diethylstilbestrol, also known as DES or stilboestrol.

Does Stilbestrol have an Orange Book patent?

No active Orange Book patent of material commercial significance is associated with the historical DES product.

Can a company launch a generic version of Stilbestrol without a Paragraph IV filing?

Patent entry risk is minimal because no meaningful unexpired listed patent appears to block entry. The applicable FDA pathway and approval requirements would depend on the proposed dosage form and product status.

Does Stilbestrol have biosimilar competition?

No. Biosimilars apply to biological products. Diethylstilbestrol is a chemically synthesized small molecule, so any competition would involve generic or compounded products rather than biosimilars.

References

1. National Cancer Institute. (n.d.). Diethylstilbestrol (DES) exposure. https://www.cancer.gov/about-cancer/causes-prevention/risk/hormones/des-fact-sheet

2. U.S. Food and Drug Administration. (1971). Diethylstilbestrol contraindicated in pregnancy. FDA Drug Bulletin.

3. U.S. Food and Drug Administration. (n.d.). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/

4. Centers for Disease Control and Prevention. (n.d.). About DES exposure. https://www.cdc.gov/des/

5. U.S. Food and Drug Administration. (n.d.). Drugs@FDA. https://www.accessdata.fda.gov/scripts/cder/daf/