LIOTRIX (T4;T3) - Generic Drug Details

What are the generic drug sources for liotrix (t4;t3) and what is the scope of patent protection?

Liotrix (t4;t3) is the generic ingredient in ten branded drugs marketed by Parke Davis and Allergan, and is included in two NDAs. Additional information is available in the individual branded drug profile pages.

Summary for LIOTRIX (T4;T3)

US Patents:	0
Tradenames:	10
Applicants:	2
NDAs:	2
Raw Ingredient (Bulk) Api Vendors:	11
DailyMed Link:	LIOTRIX (T4;T3) at DailyMed

US Patents and Regulatory Information for LIOTRIX (T4;T3)

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Allergan	THYROLAR-5	liotrix (t4;t3)	TABLET;ORAL	016807-006	Approved Prior to Jan 1, 1982		DISCN	No	No
Allergan	THYROLAR-2	liotrix (t4;t3)	TABLET;ORAL	016807-002	Approved Prior to Jan 1, 1982		DISCN	Yes	No
Parke Davis	EUTHROID-1	liotrix (t4;t3)	TABLET;ORAL	016680-002	Approved Prior to Jan 1, 1982		DISCN	No	No
Parke Davis	EUTHROID-3	liotrix (t4;t3)	TABLET;ORAL	016680-004	Approved Prior to Jan 1, 1982		DISCN	No	No

Liotrix (T4/T3) Market Dynamics, Patent Status, and Financial Trajectory

Last updated: September 6, 2026

Liotrix, a fixed-dose combination of levothyroxine sodium (T4) and liothyronine sodium (T3), has moved from a branded pharmaceutical product to a largely inactive U.S. market category. The historical brand Thyrolar lost commercial momentum after prolonged supply and manufacturing problems. No active patent estate or meaningful regulatory exclusivity protects the product, and no publicly reported standalone revenue stream exists today.

The commercial opportunity is constrained by dominant levothyroxine monotherapy, limited clinical support for routine T4/T3 combination treatment, manufacturing complexity, and the availability of compounded alternatives. A new sponsor could pursue a 505(b)(2) product, but the addressable market would likely be niche unless supported by differentiated dosing, supply reliability, clinical data, or a new delivery system.

What is liotrix and how is it used?

Liotrix combines synthetic T4 and T3 in a fixed formulation. Historically, Thyrolar was supplied in tablet strengths measured in grains, including 1/4-, 1/2-, 1-, and 2-grain products. The product was intended for thyroid hormone replacement in hypothyroidism.

The pharmacologic rationale is straightforward: T4 provides a longer-acting thyroid hormone reservoir, while T3 has more rapid activity. The commercial and clinical problem is that T3 produces higher serum peaks and has a shorter half-life than T4. This creates dose-management and tolerability issues, including potential cardiovascular and skeletal risks when exposure is excessive.

The American Thyroid Association has recommended levothyroxine as the standard treatment for primary hypothyroidism and has not established routine T4/T3 combination therapy as superior for most patients.[1]

Historical product profile

Attribute	Liotrix
Active ingredients	Levothyroxine sodium and liothyronine sodium
Common historical brand	Thyrolar
Dosage form	Oral tablet
Historical strength convention	Grain-based strengths
Therapeutic area	Hypothyroidism
Primary U.S. sponsor history	Forest Laboratories and successor organizations
Current product class	Legacy thyroid replacement product
Biologic status	Not a biologic
Biosimilar pathway	Not applicable

What is the current FDA status of liotrix?

Liotrix has historical FDA approval as a prescription thyroid replacement product, but commercial availability has been impaired for years. Thyrolar was associated with extended manufacturing and supply interruptions. FDA shortage and discontinuation records have identified liotrix products as unavailable or not commercially supplied during periods of the product’s decline.[2]

The product’s current market position is materially different from that of an actively marketed branded drug:

1. It does not have a commercially visible branded franchise comparable to levothyroxine.
2. It has no active biologic exclusivity or biosimilar protection.
3. Its historical approval does not create meaningful modern commercial momentum.
4. Compounded liotrix may be available through specialty pharmacies, but compounded supply is separate from an FDA-approved, mass-market product.

FDA’s Orange Book framework distinguishes products discontinued for commercial reasons from products withdrawn for safety or effectiveness concerns. A discontinued listing does not itself imply that the active ingredients are unsafe or ineffective.[3]

What is the Orange Book status of liotrix?

The relevant issue is not patent exclusivity but discontinued-product status and reference-product utility. Historical liotrix listings may remain visible in FDA databases even when the product is no longer actively distributed.

A sponsor seeking to reintroduce liotrix would need to establish the applicable regulatory pathway, reference product status, manufacturing controls, bioequivalence strategy, and labeling position. An ANDA route could be difficult if the reference product and market status do not provide a clean path. A 505(b)(2) application could offer greater flexibility for a reformulated or differentiated product.

When does liotrix lose exclusivity?

Liotrix’s meaningful patent and regulatory exclusivity expired decades ago. The active ingredients are old small molecules, and the historical Thyrolar franchise does not have a currently relevant patent barrier comparable to those protecting newer pharmaceutical products.

Patent estate

Protection category	Current commercial relevance
Composition-of-matter patents	Expired
Historical product patents	Expired or commercially immaterial
T4/T3 combination claims	Vulnerable to prior-art and obviousness challenges
Basic tablet formulation patents	Expired or readily designed around
Method-of-use patents	No material exclusivity identified for routine replacement
Manufacturing patents	Potentially relevant only to a new process or formulation
Regulatory exclusivity	No meaningful current exclusivity identified

A new liotrix product could obtain patents on a novel ratio, modified-release profile, device, formulation, or manufacturing process. Those patents would protect the new product’s technical implementation rather than restore exclusivity to conventional liotrix tablets.

How many patents cover liotrix?

No meaningful active U.S. patent estate appears to protect conventional liotrix as a legacy T4/T3 tablet. Patent-count analysis is therefore less useful than claim-scope analysis.

A conventional product using known levothyroxine and liothyronine salts in an immediate-release tablet would face weak composition and formulation protection. Potentially stronger claims would require technical differentiation, such as:

• Controlled or biphasic release of T3 and T4.
• Circadian or chronotherapy-based dosing.
• Reduced T3 peak exposure.
• Stabilized T3 content during shelf life.
• Improved dissolution or bioavailability.
• Patient-specific dose delivery.
• A novel fixed ratio supported by clinical outcomes.

These claims would face prior-art risks because thyroid hormone combinations, sustained-release formulations, and individualized dosing have been extensively discussed in the scientific and patent literature.

What caused the decline of the Thyrolar market?

The decline resulted from supply disruption combined with weak demand economics. Thyrolar lacked the scale and market power of levothyroxine products, while production required reliable handling of two active pharmaceutical ingredients with different stability and dosing characteristics.

The commercial pressures included:

• Repeated manufacturing interruptions.
• Low prescription volume relative to levothyroxine.
• Limited guideline support for routine combination treatment.
• Availability of generic levothyroxine.
• Availability of desiccated thyroid products for patients seeking T4/T3 exposure.
• Compounded alternatives for physicians and patients requiring customized ratios.
• Limited ability to pass manufacturing costs into pricing.

The key competitor is not another branded liotrix product. It is levothyroxine monotherapy, which is inexpensive, widely available, familiar to prescribers, and supported by treatment guidelines.

How does liotrix compare with levothyroxine and desiccated thyroid?

Product	Composition	Market position	Key commercial advantage	Key limitation
Levothyroxine	T4 only	Dominant standard therapy	Low cost, broad availability, guideline support	Does not provide direct T3
Liotrix	Synthetic T4 plus T3	Legacy and niche	Fixed synthetic combination	Supply, evidence, and dosing concerns
Desiccated thyroid extract	Animal-derived T4 plus T3 and other thyroid components	Alternative thyroid replacement category	Established patient preference segment	Variable T4:T3 profile and guideline concerns
Compounded T4/T3	Customized synthetic combination	Specialty niche	Individualized ratios and release profiles	Quality, consistency, and reimbursement issues

Levothyroxine remains the economic benchmark. Any commercial liotrix product would need to justify a price premium through improved symptom control, adherence, pharmacokinetics, supply reliability, or clinical differentiation.

What is the financial trajectory for liotrix?

The financial trajectory is best characterized as decline, discontinuation, and niche substitution rather than growth.

Public company filings have not reported a meaningful standalone revenue line for liotrix in recent years. Historical Thyrolar sales were embedded within broader pharmaceutical portfolios, making product-level revenue reconstruction unreliable. The product’s commercial deterioration is evident from supply discontinuity and the absence of a sustained branded relaunch, but there is no verified public basis for assigning a current annual revenue figure.

Financial trajectory

Period	Commercial condition	Financial interpretation
Early branded period	Established prescription thyroid product	Recurring but limited specialty revenue
Generic thyroid expansion	Levothyroxine gained scale	Pricing and volume pressure
Manufacturing interruption period	Repeated shortages and reduced availability	Revenue erosion and prescriber substitution
Post-discontinuation period	Compounding and alternatives filled demand	No meaningful branded revenue base
Current market	Niche or inactive approved-product segment	Commercial opportunity depends on relaunch strategy

The addressable market is larger than the revenue opportunity for conventional liotrix. Many patients use levothyroxine, but only a small subset seeks T4/T3 combination therapy. That distinction limits conversion potential.

A relaunch could generate revenue through a premium specialty product, but a low-cost generic tablet would face weak margins, limited differentiation, and uncertain physician adoption. The stronger economic case would involve a proprietary modified-release product supported by clinical evidence.

What generic entry risks exist for liotrix?

Generic entry risk is high for any conventional immediate-release liotrix tablet because the active ingredients are old and the basic dosage concept is well known. A new sponsor would need to manage:

• Demonstration of pharmaceutical equivalence.
• Bioequivalence across both T4 and T3 components.
• Assay and content-uniformity controls.
• Stability of liothyronine during storage.
• Dose conversion across grain-based and microgram-based labeling.
• Narrow therapeutic index concerns.
• Substitution and therapeutic-equivalence questions.
• Manufacturing reliability for low-volume demand.

A conventional product could be vulnerable to an ANDA or 505(b)(2) competitor if a suitable reference pathway exists. A modified-release or novel-dose product could obtain stronger protection, but it would also face greater clinical and regulatory costs.

What formulation patents could protect a new liotrix product?

Formulation patents are the most credible route to a defensible new liotrix franchise. Potential claims could cover:

1. Separate T4 and T3 release phases.
2. Delayed T3 release designed to reduce early serum peaks.
3. Tablet matrices that stabilize liothyronine.
4. Fixed ratios linked to pharmacokinetic outcomes.
5. Extended-release capsules or multiparticulates.
6. Liquid or orally disintegrating formulations.
7. Dosing systems that separate morning T4 from later T3 delivery.
8. Patient-specific combinations produced through a regulated platform.

A patent estate would be stronger if claims included measured pharmacokinetic limits, dissolution requirements, stability data, and clinical endpoints. Broad claims to “a combination of T4 and T3” would face substantial validity risk.

What licensing deals and ownership changes affect liotrix?

The historical Thyrolar business was associated with Forest Laboratories. Forest was acquired by Actavis in 2014, and Actavis later became part of Allergan. AbbVie acquired Allergan in 2020.[4][5]

These corporate transactions changed portfolio ownership but did not produce a visible modern liotrix relaunch. No major recent licensing transaction has established liotrix as a strategic growth asset. The product’s commercial value appears to be limited relative to the cost of rebuilding manufacturing, regulatory, and physician-support infrastructure.

What litigation affects liotrix?

No major active patent litigation involving conventional liotrix is a central market issue. The absence of litigation reflects the absence of a valuable active patent estate and the product’s limited commercial scale.

The principal legal risks for a new entrant would arise from:

• Patent challenges to a modified-release formulation.
• Hatch-Waxman litigation over a 505(b)(2) product.
• Orange Book listing disputes.
• Labeling claims relating to combination therapy.
• Product-liability exposure from T3-associated overreplacement.
• Compounding and state pharmacy regulation.
• Manufacturing and content-uniformity enforcement.

What is the geographic market outlook for liotrix?

The United States has the clearest historical association with Thyrolar and the strongest regulatory framework for assessing a relaunch. Outside the United States, T4/T3 combination products, compounded preparations, and thyroid extracts may be available through different national pathways.

Geographic expansion would face several barriers:

• Country-specific approval requirements.
• Different standards for combination thyroid therapy.
• Local reference-product rules.
• Reimbursement differences.
• National shortages of thyroid hormone products.
• Variable acceptance of compounded or modified-release preparations.

A sponsor would likely prioritize the United States, Canada, the United Kingdom, and selected European markets only after proving commercial demand and manufacturing reliability.

How strong is the commercial case for a liotrix relaunch?

The conventional liotrix case is weak. The differentiated-product case is stronger but remains speculative without clinical evidence.

Scenario analysis

Scenario	Product concept	Market outcome
Low investment	Conventional immediate-release tablet	Low margin, high substitution risk
Moderate investment	Reliable branded fixed-dose product	Niche revenue with limited differentiation
Higher investment	Modified-release T4/T3 product	Greater pricing potential and patent value
Specialty strategy	Compounding platform or customized dosing	Narrow market, operational and regulatory complexity
Partnership strategy	Licensing to thyroid-focused company	Lower internal commercialization burden

The most attractive asset would not be legacy liotrix itself. It would be a clinically differentiated T4/T3 delivery system that addresses T3 pharmacokinetics and demonstrates value over levothyroxine monotherapy.

Key Takeaways

• Liotrix is a legacy T4/T3 combination with a severely reduced U.S. commercial footprint.
• Thyrolar’s decline was driven primarily by supply and manufacturing problems, weak scale, and competition from levothyroxine.
• No meaningful active patent estate protects conventional liotrix tablets.
• No biosimilar risk applies because liotrix is a small-molecule product, not a biologic.
• Public filings do not provide a reliable current standalone liotrix revenue figure.
• Compounded T4/T3 products and desiccated thyroid extract occupy the remaining niche demand.
• A conventional relaunch would face weak differentiation and generic-entry risk.
• A modified-release or pharmacokinetically differentiated formulation offers the strongest patent and commercial pathway.
• The investment case depends on clinical proof, reliable manufacturing, and premium positioning rather than recovery of the historical Thyrolar franchise.

FAQs About Liotrix Market and Exclusivity

Is liotrix still commercially available in the United States?

Historically marketed Thyrolar products have been subject to prolonged discontinuation and supply problems. Current access is more commonly associated with compounded preparations or alternative thyroid products than with a broadly distributed branded liotrix tablet.

Does liotrix have an active Orange Book patent?

Conventional liotrix does not have a commercially meaningful active patent estate comparable to newer branded drugs. Historical database listings do not create new exclusivity.

Can a company launch a generic version of liotrix?

Potentially, but the regulatory path depends on the reference product, active listing status, formulation, and FDA requirements. A 505(b)(2) pathway may be more practical for a differentiated formulation.

Why is liotrix less common than levothyroxine?

Levothyroxine has guideline support, low cost, broad distribution, and predictable manufacturing economics. Liotrix adds T3, which creates more complex pharmacokinetics and has not demonstrated routine superiority for most patients.

What would make a new liotrix product commercially successful?

The strongest drivers would be reliable supply, controlled T3 release, clear clinical benefit, protected formulation technology, and reimbursement that supports pricing above generic levothyroxine.

References

1. Jonklaas, J., Bianco, A. C., Bauer, A. J., Burman, K. D., Cappola, A. R., Celi, F. S., Cooper, D. S., Kim, B. W., Peiris, A. N., Rosenthal, M. S., & Sawka, A. M. (2014). Guidelines for the treatment of hypothyroidism. Thyroid, 24(12), 1670-1751. https://doi.org/10.1089/thy.2014.0028

2. U.S. Food and Drug Administration. (n.d.). Drug shortages: Liotrix tablets and thyroid hormone products. FDA Drug Shortages Database. https://www.accessdata.fda.gov/scripts/drugshortages/

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

4. Actavis plc. (2014). Actavis completes acquisition of Forest Laboratories. Company announcement.

5. AbbVie Inc. (2020). AbbVie completes acquisition of Allergan. Company announcement.