Last updated: August 1, 2026
Propoxyphene hydrochloride and acetaminophen is a discontinued opioid combination with no active U.S. commercial market, no current FDA-approved product, and no meaningful forward sales opportunity under the existing regulatory framework. The FDA required withdrawal of all propoxyphene-containing products in 2010 after evidence linked the drug to dose-dependent cardiac conduction abnormalities, including QT-interval prolongation, torsades de pointes, ventricular tachycardia, and sudden death.[1][2]
The product’s commercial position is materially different from that of an active generic opioid. A new entrant would face a full regulatory and safety reassessment, severe controlled-substance requirements, limited clinical utility, and competition from safer analgesic alternatives. The practical market projection is therefore zero for legitimate U.S. sales unless a sponsor develops a new, clinically differentiated product and obtains new approval.
What is propoxyphene hydrochloride and acetaminophen?
Propoxyphene hydrochloride and acetaminophen is an oral analgesic combination containing the opioid propoxyphene hydrochloride and the non-opioid analgesic acetaminophen. Historical products were used for mild to moderate pain.
The formulation is distinct from propoxyphene napsylate products such as Darvocet-N. Propoxyphene hydrochloride combinations were marketed under names including Darvon Compound and generic equivalents, while propoxyphene napsylate plus acetaminophen was associated with Darvocet and Darvocet-N.
| Attribute |
Historical product profile |
| Active ingredients |
Propoxyphene hydrochloride and acetaminophen |
| Drug class |
Opioid analgesic combination |
| Dosage form |
Immediate-release oral tablet |
| Historical indication |
Mild to moderate pain |
| U.S. regulatory status |
Withdrawn from the market |
| Controlled-substance status |
Schedule IV during historical U.S. marketing |
| Current U.S. availability |
No FDA-approved marketed product |
| Main safety concerns |
Cardiac toxicity, respiratory depression, overdose, dependence, acetaminophen hepatotoxicity |
| Commercial outlook |
No conventional market forecast; effectively zero approved-product sales |
Propoxyphene had a relatively narrow therapeutic margin. The FDA concluded that the cardiac risks were present even at therapeutic doses and were not adequately offset by the drug’s analgesic benefits.[1]
When did propoxyphene hydrochloride and acetaminophen lose exclusivity?
Propoxyphene hydrochloride and acetaminophen lost commercial exclusivity before the FDA withdrawal because multiple generic versions had entered the market. The principal commercial products were old, immediate-release combination tablets, and no meaningful patent-based exclusivity remained when the products were removed.
The relevant commercial timeline is:
| Period |
Event |
| 1950s-1960s |
Propoxyphene products introduced in the United States |
| 1970s-1990s |
Combination products marketed by originators and generic manufacturers |
| 2000s |
Generic competition and increasing safety scrutiny |
| 2009 |
FDA required stronger warnings and a boxed warning after cardiac safety findings |
| November 19, 2010 |
FDA requested withdrawal of all propoxyphene products from the U.S. market |
| December 2010 |
U.S. manufacturers completed product withdrawal |
| 2011 onward |
No approved U.S. commercial market for propoxyphene products |
The withdrawal, rather than patent expiration, ended the U.S. product opportunity. Any historical formulation or method-of-use patents would have expired or become commercially irrelevant by the time of withdrawal.
What is the FDA regulatory status of propoxyphene and acetaminophen?
The FDA has determined that the risks of propoxyphene outweigh its benefits. The agency requested voluntary withdrawal after reviewing new electrocardiographic data showing clinically significant changes in cardiac electrical activity.[1]
The FDA’s 2010 action applied to all propoxyphene-containing products, including combination products with acetaminophen. The agency stated that propoxyphene could cause serious or fatal heart-rhythm abnormalities, particularly in overdose situations or when combined with other medicines that affect cardiac conduction.[1]
The European Medicines Agency reached a comparable conclusion earlier. In 2009, it recommended withdrawal of dextropropoxyphene-containing medicines from the European Union because the risks, including fatal overdose and cardiac toxicity, outweighed the benefits.[3]
FDA status summary
| Regulatory question |
Status |
| Is propoxyphene hydrochloride/acetaminophen FDA-approved today? |
No marketed approval remains |
| Can a pharmacy dispense legacy product? |
No legitimate U.S. commercial supply is expected |
| Was the product withdrawn for patent reasons? |
No |
| Was withdrawal linked to safety? |
Yes |
| Did FDA identify a safe lower dose? |
No; the agency concluded that risk could not be adequately mitigated |
| Is acetaminophen itself withdrawn? |
No; the action concerned propoxyphene-containing products |
A sponsor seeking to reintroduce the combination would need to address the safety findings through a new regulatory submission. Historical approval does not provide a practical shortcut to commercialization.
Are there active clinical trials for propoxyphene hydrochloride and acetaminophen?
There is no established active clinical-development program for propoxyphene hydrochloride and acetaminophen. The clinical literature is concentrated in four areas:
- Cardiac electrophysiology and QT prolongation.
- Fatal and nonfatal overdose.
- Respiratory depression and opioid toxicity.
- Historical efficacy comparisons with other analgesics.
The most important modern clinical evidence was the FDA-sponsored ECG study that evaluated therapeutic and supratherapeutic exposure. The study showed dose-dependent QT-interval prolongation, supporting the regulatory conclusion that propoxyphene presented a cardiac risk not justified by its modest analgesic benefit.[2]
The drug is not a conventional pipeline asset. Clinical activity involving propoxyphene is generally retrospective, toxicological, epidemiological, or forensic rather than directed toward label expansion or commercialization.
| Clinical-development category |
Current position |
| New efficacy trials |
No established development program |
| Phase 1 studies |
No commercial redevelopment program |
| Phase 2 studies |
None of practical relevance |
| Phase 3 registration trials |
None |
| Postmarketing safety studies |
Historical data only |
| Toxicology and overdose research |
Ongoing academic or forensic interest may exist |
| Regulatory label-expansion studies |
None |
A new clinical program would face an unfavorable benefit-risk starting point. A sponsor would need to demonstrate a compelling therapeutic advantage over non-opioid analgesics and other opioids while controlling cardiac, respiratory, dependence, and overdose risks.
What patents protected propoxyphene hydrochloride and acetaminophen?
The historical patent estate is no longer commercially relevant in the United States. Propoxyphene was introduced decades ago, and the combination products were subject to generic competition well before market withdrawal.
The relevant intellectual-property categories were:
Active-ingredient patents
Patents covering the propoxyphene molecule and its salt forms were historically important but expired many years ago. The hydrochloride salt did not create a modern exclusivity position after generic products became available.
Combination-product patents
Patents covering propoxyphene with acetaminophen were directed to fixed-dose oral analgesic compositions. Any such patents would have expired before the 2010 withdrawal.
Formulation patents
Historical immediate-release tablet formulations did not create durable protection. The formulation was technically straightforward and had extensive generic substitution.
Method-of-use patents
Older pain-treatment methods involving propoxyphene are also expired or commercially unusable. A new method-of-use patent would not overcome the fundamental safety issue unless the sponsor identified a new, clinically defensible indication.
Manufacturing patents
Manufacturing and salt-formation methods may have been protected historically, but those rights do not prevent current manufacture of a chemically old compound. Current barriers are regulatory, safety-related, controlled-substance, and commercial rather than patent-based.
| Patent category |
Commercial position |
| Propoxyphene compound |
Expired |
| Propoxyphene hydrochloride salt |
Expired or commercially irrelevant |
| Acetaminophen combination |
Expired |
| Immediate-release tablet |
Expired or weak |
| Pain method of use |
Expired |
| Manufacturing process |
No meaningful barrier to legacy chemistry |
| Current blocking patent |
None identified as commercially material |
What was the Orange Book status of propoxyphene hydrochloride and acetaminophen?
Propoxyphene products were historically listed in FDA approval records and the Orange Book, but their regulatory withdrawal removed the products from the active U.S. commercial market. The Orange Book is not a source of ongoing market exclusivity for a withdrawn product.
The central Orange Book implications are:
- Historical approved applications do not establish current commercial availability.
- A withdrawn product cannot support a normal generic launch strategy.
- Paragraph IV litigation is not a meaningful current pathway for this drug.
- Any historical listed patents have no practical blocking effect today.
- A company cannot rely on an old ANDA or old product listing to avoid the need for a viable FDA-approved product.
The regulatory pathway for a future entrant would depend on the specific development strategy. A sponsor could potentially seek approval for a new product, but the application would face the prior safety record and FDA’s withdrawal determination.
Are there Paragraph IV challenges or generic litigation?
No current Paragraph IV challenge is commercially material because the reference products were withdrawn and the relevant patent terms expired. Historical generic competition occurred before the 2010 withdrawal, but the market did not develop into a current patent dispute.
The principal legal issues surrounding propoxyphene have involved:
- Product-liability claims.
- Wrongful-death allegations.
- Failure-to-warn theories.
- Regulatory and manufacturer conduct.
- Claims associated with cardiac toxicity and overdose.
These matters are distinct from ANDA patent litigation. A Paragraph IV certification is valuable when a generic sponsor seeks approval against an active reference product protected by listed patents. That framework has little practical relevance to a withdrawn opioid combination with no viable current reference-market opportunity.
What patent litigation and settlement agreements affected the product?
The commercial history is not defined by a current patent settlement. The important legal event was regulatory withdrawal, followed by product-liability and consumer litigation involving propoxyphene manufacturers.
No settlement agreement creates a current market-entry right for a generic manufacturer. No known agreement restores U.S. commercialization or removes the FDA’s safety concerns.
For diligence purposes, the distinction is important:
| Issue |
Current relevance |
| ANDA patent litigation |
Minimal |
| Paragraph IV settlement |
No material current effect |
| Product-liability litigation |
Historically significant |
| FDA withdrawal |
Decisive |
| Manufacturing dispute |
Not a principal barrier |
| Patent-based launch date |
None |
| Regulatory re-entry risk |
Very high |
How strong is the patent estate for propoxyphene hydrochloride and acetaminophen?
The patent estate is effectively weak because the core composition, salt, formulation, and use rights are old and expired. The product has no meaningful lifecycle-management position based on patents.
Patent strength should be assessed across five dimensions:
| Dimension |
Assessment |
| Remaining term |
None of commercial significance |
| Claim breadth |
Narrow or expired for historical products |
| Freedom to operate |
Generally favorable from a patent perspective |
| Regulatory risk |
Extremely unfavorable |
| Commercial differentiation |
Low |
| Litigation leverage |
Minimal |
A company could potentially obtain new patents on a novel delivery system, abuse-deterrent formulation, prodrug, combination, or therapeutic use. Those patents would protect the new technology, not restore the commercial value of the historical product. They would also require new clinical and regulatory support.
What generic entry risks exist?
A conventional generic launch is not the principal risk because the product is no longer an active U.S. market. The relevant risk is unauthorized or illicit distribution, compounded supply, or foreign-market diversion. Those channels do not constitute a legitimate pharmaceutical opportunity.
For a regulated sponsor, the major risks are:
- FDA refusal based on the known cardiac safety profile.
- Difficulty establishing a favorable benefit-risk balance.
- Controlled-substance manufacturing and distribution obligations.
- Opioid abuse, dependence, and overdose exposure.
- Acetaminophen-related liver toxicity.
- Product-liability claims.
- Limited prescriber demand.
- Payer and hospital reluctance.
- Competition from safer therapies.
Generic launch scenarios
| Scenario |
Probability assessment |
Commercial implication |
| Standard ANDA launch |
Not commercially viable |
No meaningful market |
| Reintroduction of historical tablet |
Regulatory risk is prohibitive |
Unattractive |
| New abuse-deterrent formulation |
Requires substantial development |
Possible only with major differentiation |
| New prodrug or targeted delivery system |
Patentable but high-risk |
New product, not a generic launch |
| Foreign-market continuation |
Jurisdiction-specific and restricted |
Limited, declining opportunity |
| Academic toxicology use |
Possible |
No material pharmaceutical revenue |
How does propoxyphene compare with competing analgesics?
Propoxyphene was disadvantaged by modest efficacy and disproportionate safety risk. It competed historically with codeine combinations, tramadol, nonsteroidal anti-inflammatory drugs, and acetaminophen-based products.
| Product category |
Relative commercial position |
| Propoxyphene/acetaminophen |
Withdrawn in the U.S.; cardiac and overdose concerns |
| Codeine/acetaminophen |
Active in some markets; opioid and acetaminophen risks remain |
| Tramadol |
Active in many markets; seizure, serotonin, dependence, and opioid risks |
| NSAIDs |
Broad use; gastrointestinal, renal, and cardiovascular risks |
| Acetaminophen alone |
Broad use; liver toxicity at excessive doses |
| Newer opioid formulations |
Stronger clinical and commercial infrastructure |
The comparison favors alternatives because propoxyphene did not offer a sufficiently distinct efficacy or tolerability advantage. Its historical positioning as a weaker opioid did not eliminate serious toxicity.
What is the market size and revenue projection?
There is no credible positive revenue forecast for propoxyphene hydrochloride and acetaminophen as a currently marketed U.S. drug. The product was withdrawn, and no active approved-product sales base supports a conventional CAGR model.
| Market metric |
Projection |
| Current U.S. branded sales |
Zero |
| Current U.S. generic sales |
No legitimate marketed base |
| U.S. prescription growth |
None |
| Patent-protected revenue window |
None |
| Expected standard generic revenue |
Zero or immaterial |
| Re-entry investment case |
Negative under historical formulation |
| Potential value of a redesigned product |
Dependent on new clinical evidence and approval |
A financial model that assigns revenue to a generic re-entry would overstate the asset’s value. The appropriate base case is no commercial revenue. An upside case would require a new molecular, formulation, or delivery technology with a separate clinical-development program.
Revenue exposure
Historical manufacturers and distributors faced exposure from:
- Product withdrawal.
- Inventory destruction or returns.
- Lost opioid revenue.
- Regulatory compliance costs.
- Litigation and settlement costs.
- Reputational and portfolio effects.
The product’s withdrawal did not materially create a new branded monopoly for substitute analgesics. Demand shifted across existing opioid and non-opioid products.
What manufacturing and intellectual-property barriers remain?
The chemistry of propoxyphene hydrochloride and acetaminophen is not the main barrier. The principal barriers are regulatory and operational.
A manufacturer would need to address:
- Controlled-substance registration.
- Quota and inventory controls.
- Good manufacturing practice compliance.
- Analytical testing for identity, potency, impurities, and content uniformity.
- Acetaminophen dose-control requirements.
- Abuse, diversion, and suspicious-order monitoring.
- Pharmacovigilance.
- Labeling and risk-management obligations.
- Product-liability insurance and reserve requirements.
The manufacturing process is comparatively conventional. The challenge is producing and distributing a product that the FDA has determined has an unfavorable benefit-risk profile.
What is the outlook for biosimilar risk?
Propoxyphene hydrochloride and acetaminophen is a small-molecule drug, not a biologic. Biosimilar competition does not apply. Any future competition would arise through an ANDA, a 505(b)(2) application, or a new drug application, depending on the product’s formulation and clinical differences.
| Regulatory pathway |
Relevance |
| Biosimilar application |
Not applicable |
| ANDA |
Theoretically relevant to an approved reference product, but not commercially practical here |
| 505(b)(2) application |
Potential route for a substantially modified product |
| Full NDA |
Likely for a materially new formulation or clinical use |
| Compounded product |
Not a substitute for FDA-approved commercial development |
Key Takeaways
- Propoxyphene hydrochloride and acetaminophen is a withdrawn opioid analgesic combination.
- The FDA required withdrawal of all propoxyphene products in 2010 because of cardiac toxicity and overdose risk.[1]
- No active U.S. commercial market or meaningful patent exclusivity remains.
- Current clinical activity is largely toxicological, epidemiological, and historical, not commercial development.
- Paragraph IV litigation and generic patent settlements are not material current issues.
- The historical formulation has no attractive re-entry case.
- A new product would require substantial clinical, regulatory, and safety differentiation.
- Biosimilar competition is irrelevant because propoxyphene is a small molecule.
- The appropriate base-case revenue projection is zero for a conventional generic or reintroduced historical tablet.
FAQs
Is propoxyphene hydrochloride the same as Darvocet?
No. Darvocet was primarily associated with propoxyphene napsylate and acetaminophen. Propoxyphene hydrochloride was used in other historical combination products, including formulations marketed as Darvon Compound.
Can propoxyphene and acetaminophen still be prescribed in the United States?
No legitimate FDA-approved U.S. commercial supply is expected after the FDA-directed withdrawal of propoxyphene products in 2010.
Did propoxyphene fail because of acetaminophen?
No. The principal withdrawal concern was propoxyphene-related cardiac toxicity. Acetaminophen added a separate risk of liver injury at excessive doses.
Could a company patent a new propoxyphene formulation?
A genuinely novel formulation, delivery system, prodrug, or use could potentially receive patent protection. That patent would not eliminate the need to establish an acceptable safety and benefit-risk profile.
Is propoxyphene still available outside the United States?
Availability varies by country, but the European Union also moved to withdraw dextropropoxyphene-containing medicines after safety review.[3] Any remaining foreign-market status requires jurisdiction-specific verification and does not create a U.S. launch opportunity.
References
-
U.S. Food and Drug Administration. (2010, November 19). FDA recommends against continued use of propoxyphene. https://www.fda.gov/drugs/drug-safety-and-availability/fda-recommends-against-continued-use-propoxyphene
-
U.S. Food and Drug Administration. (2010). Propoxyphene: Withdrawal of approval of new drug applications and abbreviated new drug applications. Federal Register, 75 Fed. Reg. 74,914.
-
European Medicines Agency. (2009). European Medicines Agency recommends withdrawal of dextropropoxyphene-containing medicines. https://www.ema.europa.eu
-
U.S. Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
-
U.S. Food and Drug Administration. (2010). FDA Drug Safety Communication: FDA recommends against the continued use of propoxyphene. https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/fda-drug-safety-communication-fda-recommends-against-continued-use-propoxyphene
