SILENOR Drug Patent Profile

When do Silenor patents expire, and what generic alternatives are available?

Silenor is a drug marketed by Currax and is included in one NDA. There are sixteen patents protecting this drug and one Paragraph IV challenge.

This drug has sixteen patent family members in four countries.

The generic ingredient in SILENOR is doxepin hydrochloride. There are seven drug master file entries for this compound. Fifty suppliers are listed for this compound. Additional details are available on the doxepin hydrochloride profile page.

DrugPatentWatch^® Litigation and Generic Entry Outlook for Silenor

A generic version of SILENOR was approved as doxepin hydrochloride by MYLAN PHARMS INC on May 13^th, 1986.

Summary for SILENOR

International Patents:	16
US Patents:	16
Applicants:	1
NDAs:	1
Patent Litigation and PTAB cases:	See patent lawsuits and PTAB cases for SILENOR

Paragraph IV (Patent) Challenges for SILENOR

Tradename	Dosage	Ingredient	Strength	NDA	ANDAs Submitted	Submissiondate
SILENOR	Tablets	doxepin hydrochloride	3 mg and 6 mg	022036	2	2010-09-16

US Patents and Regulatory Information for SILENOR

SILENOR is protected by sixteen US patents.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Currax	SILENOR	doxepin hydrochloride	TABLET;ORAL	022036-002	Mar 17, 2010	AB	RX	Yes	Yes	9,532,971		Y
Currax	SILENOR	doxepin hydrochloride	TABLET;ORAL	022036-002	Mar 17, 2010	AB	RX	Yes	Yes	11,110,074
Currax	SILENOR	doxepin hydrochloride	TABLET;ORAL	022036-002	Mar 17, 2010	AB	RX	Yes	Yes	11,096,920
Currax	SILENOR	doxepin hydrochloride	TABLET;ORAL	022036-001	Mar 17, 2010	AB	RX	Yes	No	9,861,607
Currax	SILENOR	doxepin hydrochloride	TABLET;ORAL	022036-002	Mar 17, 2010	AB	RX	Yes	Yes	9,486,437
Currax	SILENOR	doxepin hydrochloride	TABLET;ORAL	022036-002	Mar 17, 2010	AB	RX	Yes	Yes	9,861,607

International Patents for SILENOR

See the table below for patents covering SILENOR around the world.

Country	Patent Number	Title	Estimated Expiration
Israel	116674	MICROCRYSTALLINE CELLULOSE-BASED EXCIPIENT HAVING IMPROVED COMPRESSIBILITY, PHARMACEUTICAL COMPOSITIONS CONTAINING THE SAME AND METHODS FOR THE PREPARATION OF SAID EXCIPIENT AND OF SOLID DOSAGE FORM THEREOF
World Intellectual Property Organization (WIPO)	2008011150
European Patent Office	2026792	FORMULATIONS DE DOXÉPINE À FAIBLE DOSE, INCLUANT DES FORMULATIONS BUCCALES, SUBLINGUALES ET À DISSOLUTION RAPIDE, ET LEURS UTILISATIONS POUR TRAITER L'INSOMNIE (LOW DOSE DOXEPIN FORMULATIONS, INCLUDING BUCCAL, SUBLINGUAL AND FASTMELT FORMULATIONS, AND USES OF THE SAME TO TREAT INSOMNIA)
Canada	2183882	EXCIPIENT PHARMACEUTIQUE A COMPRESSIBILITE AMELIOREE (PHARMACEUTICAL EXCIPIENT HAVING IMPROVED COMPRESSIBILITY)
Norway	321771
Japan	3728321

Investment Scenario and Fundamentals Analysis: SILENOR (Doxepin)

Last updated: April 26, 2026

What is SILENOR and how is it used?

SILENOR is a prescription medicine containing doxepin for the treatment of sleep maintenance insomnia in adults. The product is marketed in the U.S. in a low-dose formulation intended to improve sustained sleep rather than provide broad sedative effects.

Core commercial framing

• Indication: sleep maintenance insomnia
• Patient segment: adults with difficulty staying asleep
• Market need: chronic insomnia treatment requiring predictable nighttime efficacy with tolerability

How big is the market and where does SILENOR fit?

The insomnia treatment landscape splits by diagnosis type (sleep onset vs sleep maintenance) and by drug class. SILENOR competes primarily in the sleep maintenance insomnia segment, where clinicians and payers favor therapies with:

• predictable onset during nighttime dosing
• tolerability that supports longer-term prescribing
• reduced next-day impairment relative to some older sedatives

Competitive reference set (by treatment objective rather than exact chemistry)

• Sleep maintenance insomnia therapies (pharmacologic)
• Non-benzodiazepine hypnotics and related agents (class-level competition)
• Behavioral insomnia approaches (non-drug competition for payer and guideline influence)

What are the fundamental drivers of revenue?

Revenue drivers

1. Prescriber adoption for sleep maintenance insomnia rather than off-label use for sleep onset insomnia.
2. Formulary position: tier placement, prior authorization, and step edits.
3. Net price discipline: rebates and discounts tied to payer contracting.
4. Safety and tolerability profile: persistence in therapy and fewer discontinuations.
5. Competitive displacement risk from newer branded agents and generic entry dynamics.

Usage and dosing

• Low-dose doxepin is positioned for nighttime use targeting sleep maintenance.
• The dosing regimen is designed around sustained sleep effects through the night.

What is the patent and exclusivity position?

SILENOR’s long-term investment case depends on:

• Composition-of-matter and formulation protection (where applicable)
• Oral dosage form IP
• Method-of-use protection for sleep maintenance insomnia
• Regulatory exclusivity (if any) tied to the specific approved use and formulation

Impact on investment

• If enforceable exclusivity covers the specific approved dose and indication, risk shifts from immediate generic erosion to eventual “end-game” around that protection.
• If protection is narrower (e.g., only tied to formulation features), generic entry is more likely once regulatory pathways permit substitution.

What is the regulatory status and what does it imply for risk?

Regulatory risk map

• If SILENOR sits inside a period with enforceable IP barriers, generics face litigation and/or launch risk delays.
• If those barriers expire, the dominant risk becomes:
  • accelerated generic pricing compression
  • payer switching dynamics
  • loss of pharmacy channel share

Investment relevance

• For branded sleep medicines, the valuation hinge is not only sales today. It is the expected trajectory of net sales after the next IP event (expiration, settlement, or generic launch).

How strong is the competitive position?

SILENOR’s competitive position is shaped by three factors:

1. Clinical differentiation by target symptom (sleep maintenance insomnia).
2. Tolerability for nighttime use versus agents with higher adverse-effect concern.
3. Payer familiarity and contracting history with doxepin-based insomnia therapy.

Where competition typically attacks

• price and formulary exclusion pressure
• therapeutic interchange within insomnia categories
• switching by pharmacy benefit managers toward lower-cost equivalents

What are the key investment scenarios?

Scenario 1: “Protective horizon” (bull case)

• IP barriers limit generic substitution.
• Payer contracting supports stable tier placement.
• Clinical preference consolidates in sleep maintenance insomnia.

Expected outcomes

• revenue stability and steady market share
• higher resilience to category price pressure
• valuation supported by a longer branded cash-flow duration

Scenario 2: “Formulary pressure” (base case)

• SILENOR remains available and prescribed, but pays higher rebates and accepts formulary changes.
• Competitive entrants hold share by emphasizing convenience, outcomes, or payer alignment.

Expected outcomes

• modest growth or flat-to-slow decline driven by price concessions
• rising marketing and access cost
• valuation shifts toward cash-flow durability rather than expansion

Scenario 3: “Generic acceleration” (bear case)

• Loss of exclusivity leads to generic erosion.
• Net sales decline steepens due to payer switching and pharmacy substitution.

Expected outcomes

• rapid margin compression
• reduced forecast visibility
• increased litigation or settlement overhead if applicable

What metrics matter most to underwrite SILENOR?

For an investment underwriting model, focus on measures that convert prescriptions into cash:

Commercial KPIs

• Script trend (monthly, by channel)
• TRx to Rx conversion (if you track patient flows)
• Net price trajectory (invoice less rebates)
• Payer mix (commercial vs Medicare, and top plan concentration)
• Formulary status (tier and PA requirements)

Economic KPIs

• Gross-to-net compression and how it changes with contracts
• Marketing intensity as a percentage of net sales
• Channel inventory indicators (if available via management commentary)

What is the fundamental investment thesis?

SILENOR is a branded doxepin-based insomnia product focused on sleep maintenance insomnia, where commercial value depends on:

• whether it maintains formulary access and payer acceptance
• whether enforceable IP prevents or delays generic competition
• whether prescribers continue to view it as an appropriate targeted therapy versus broader hypnotic classes

Investment posture

• The upside comes from stable access plus sustained prescription capture.
• The downside comes from IP-driven generic entry and intensifying formulary substitution.

Key regulatory and market check points

Check points that typically precede repricing

• label or dosing updates that expand or narrow prescriber use
• payer policy changes (PA, step edits)
• generic launches or authorized generics in the insomnia maintenance segment
• litigation outcomes or settlements that affect launch timing

Check points that typically support persistence

• stable safety profile in real-world prescribing
• continued alignment with guideline and payer-supported care pathways
• contracting leverage and rebate discipline

What does the IP timeline imply for valuation?

A practical valuation lens for branded insomnia products is the “years of remaining exclusivity” model:

• longer exclusivity supports a longer duration of premium pricing
• shorter exclusivity compresses the time value of current cash flows
• the highest sensitivity typically appears around the next material IP event date

How to connect IP to fundamentals

• If exclusivity covers the specific approved dose and indication, the model benefits from reduced probability-weighted generic share loss.
• If exclusivity is weaker or already structurally constrained, the model should assume faster erosion and sharper net price decline at the next launch window.

What can investors do with the scenario analysis?

For business decisions

• Use scenario weights tied to IP calendar and likelihood of payer switching after generic entry.
• Stress test margins under different gross-to-net assumptions for each scenario.
• Align forecasting with formulary dynamics rather than only script counts.

For R&D and licensing strategy

• Treat insomnia maintenance as a competitive field where incremental differentiation is payer-relevant.
• If pursuing next-gen sleep maintenance therapeutics, prioritize differentiation tied to dosing, tolerability, and patient-relevant outcomes that change payer coverage behavior.

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Key Takeaways

• SILENOR is a branded doxepin therapy for sleep maintenance insomnia, and its fundamentals are driven by access, net price, and script persistence rather than broad category growth.
• The investment case is highly sensitive to formulary position and IP/exclusivity calendar, which govern generic substitution timing and net sales trajectory.
• Underwriting should rely on cash conversion metrics: scripts, net price, rebates, and channel mix, not just prescription volume.
• Scenario modeling for SILENOR should weight outcomes across protective exclusivity, formulary pressure, and generic acceleration.

FAQs

1. Is SILENOR used for sleep onset insomnia or sleep maintenance insomnia?
   It is approved for sleep maintenance insomnia.

2. What is the main investment risk for branded insomnia products like SILENOR?
   Generic substitution driven by IP/exclusivity expiration and payer switching.

3. What drives SILENOR’s net sales more than gross sales?
   Gross-to-net dynamics including rebates and payer contracting terms.

4. What is the most common competitive pressure in insomnia maintenance?
   Formulary replacement by lower-cost alternatives and therapeutic interchange within insomnia categories.

5. How should investors connect IP protection to financial forecasts?
   By mapping the expected timing of material IP events to probabilities of market share and net price erosion.

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References

[1] FDA. “Drug Approval Package: SILENOR (doxepin).” U.S. Food and Drug Administration.
[2] FDA. “Approved Drug Products with Therapeutic Equivalence Evaluations (Orange Book) for doxepin.” U.S. Food and Drug Administration.
[3] SILENOR Prescribing Information. (doxepin). U.S. FDA label.