TDF Litigation Before the California Supreme Court

The products at issue are two classes of Gilead’s lifesaving, FDA-approved medicines that, in combination with other medicines, are used to treat HIV: tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF).

Gilead researched, developed, and satisfied the rigorous FDA approval process to bring five separate TDF-based medicines to market between 2001 and 2012.

With regard to TAF-based medicines, Gilead started looking into TAF in the late 1990s, but stopped that research in 2004. The only study of TAF in humans at that time involved 20 patients taking TAF for two weeks, and that study found no safety improvement over TDF. When Gilead stopped TAF development, TDF was already approved both by itself and in a combination tablet with another HIV medicine (emtricitabine/TDF), for the treatment of HIV. Meanwhile, at that same time, the long-term safety of TAF was unknown and impossible to predict. Since 2004, consistent with FDA guidance and requests from the patient community, Gilead has developed additional TDF-based medicines for HIV treatment, including TDF-based complete single tablet regimens.

In 2010, Gilead started studying TAF again as a possible additional treatment option for the aging population of individuals taking HIV medicines. It then took five more years of clinical trials and additional research to demonstrate the safety and effectiveness of TAF to obtain FDA approval to start selling TAF-based medicines.

Timeline of Development:

• Late-1990s: Gilead begins studying tenofovir—both TDF and TAF—for the treatment of HIV
• 2001: First TDF-based medicines receive FDA approval
• 2004: Gilead concludes TAF had not distinguished itself from TDF, which had already been on the market for years and had a proven safety and effectiveness profile
• 2004 – 2010: Gilead focuses its research and development related to tenofovir on developing combination medicines containing TDF so that people living with HIV could take a single, once-a-day pill rather than the complicated cocktail of numerous different medicines they had previously been required to take
• 2010 – 2015: Gilead studies TAF as a possible additional treatment option for the aging population of individuals taking HIV medicines
• 2015: First TAF-based medicines receive FDA approval

If not overturned, the Court of Appeal’s decision to allow this liability theory could have widespread, negative ramifications across all fields of innovation and manufacturing. It could disincentivize innovation and discourage manufacturers from investigating and developing ways to improve products. As with Gilead’s early research into TAF, this work could form the basis for lawsuits targeting their earlier, non-defective products.

If the California Supreme Court affirms the lower court’s decision, the new liability rule could undermine the way in which companies develop new products and discourage them from looking for ways to improve existing products.

The California Supreme Court granted Gilead’s petition for review in May 2024.

Briefing for the California Supreme Court was completed in early 2025.

The California Supreme Court heard oral argument on May 6, 2026, and is expected to issue its decision this summer.

The following are links to Gilead’s briefs submitted to the California Court of Appeal and California Supreme Court.

• Petition for Writ of Mandamus to California Court of Appeal
  • This initial filing asked the Court of Appeal to intervene and direct the trial court to enter judgment in Gilead’s favor on plaintiffs’ claims, arguing that plaintiffs’ novel liability theories are unprecedented and impermissible because they involve side effects properly disclosed on FDA-approved, non-defective medicines.
• California Court of Appeal Reply Brief
  • This reply brief responds to the Plaintiffs’ opposition to the writ of mandamus and explains that immediate writ relief is necessary because the trial court’s ruling would force multiple unnecessary trials on legal theories that are unsupported by California law.
• California Court of Appeal Supplemental Brief
  • After oral argument, the Court of Appeal asked the parties to brief specific questions about the legal theories in the case, including those involving safer feasible alternatives, negligent design defect, and whether any duty exists to develop an alternative to an existing, non-defective product. This brief addresses those questions.
• California Court of Appeal Supplemental Response Brief
  • This brief responds to the plaintiffs’ supplemental briefing and explains that the proposed duty is both nebulous and boundless because it would leave juries to decide, after the fact, whether a manufacturer acted “reasonably” in various product development decisions.
• California Supreme Court Petition for Review
  • After the Court of Appeal ruled to allow the plaintiffs’ novel legal claims, Gilead filed this petition asking the California Supreme Court to hear the case and decide whether plaintiffs’ novel legal claims are viable under California law.
• California Supreme Court Opening Brief
  • The California Supreme Court agreed to hear the case, and, in this brief, Gilead explains the reasons plaintiffs’ legal theory should not be allowed. The brief shows that the Court of Appeal’s rule would “weaponize” innovation by exposing manufacturers to liability based on research and development decisions about products that were not yet proven safe, effective, or ready for market.
• California Supreme Court Reply Brief
  • This reply responds to the Plaintiffs’ brief in the Supreme Court, explaining that plaintiffs’ theory is based on the mischaracterization of the record, including the false assertion that Gilead knew in 2004 that TAF was safer than TDF and delayed TAF for profit.
• California Supreme Court Amicus Response Brief
  • After dozens of companies, patient advocacy groups, think tanks, academics, and trade associations filed amicus briefs in support of Gilead, Gilead filed this brief to discuss the key points from the amicus briefs, explaining that plaintiffs and the amici supporting them fail to justify expanding product liability law beyond the traditional requirement that a plaintiff prove a defect in the product that caused injury.

Given the potential widespread effects of this new legal theory, the case has drawn attention from other companies, legal scholars, the pharmaceutical industry, other manufacturing industries, health policy experts, and patient advocates—all of whom are concerned about the negative impact this new legal obligation would have on innovation, public health and the ability to serve people and patients.

In November 2024, in support of Gilead’s briefing on this matter before the California Supreme Court, 12 separate amicus briefs representing 67 signatories, were filed:

Companies (across industries):

• Archer Aviation, Bayer, Becton Dickinson, Biogen, Bristol Myers Squibb, Corteva, Cytokinetics, Inc., Dow, DuPont, Eli Lilly and Company, GE Healthcare Technologies, Inc., Genentech, General Motors, Glaukos, GSK LLC, Hamilton Beach Brands, Hyundai, Incyte, Johnson & Johnson / J&J, Kenvue, Kia, Medtronic, Merck, Organon, Pfizer, Regeneron, Roche, Sanofi, Sonoma Biotherapeutics, STORM Therapeutics, Takeda, Toyota, Vertex, Volkswagen, Zimmer Biomet
  • A group of major manufacturers, including companies in the pharmaceutical, biotechnology, medical device, automotive, consumer products, and technology sectors, filed this brief to urge the California Supreme Court to reject plaintiffs’ proposed duty. The brief shows that allowing liability for failing to commercialize a potentially safer alternative to a non-defective product would distort research and development decisions, discourage product improvements, and invite courts and juries to second-guess complex innovation choices with hindsight.
• Lyft, Textron, Uber, Viasat, Vizio
  • These technology companies further demonstrate that the Court of Appeal’s rule would threaten innovation across technology-driven industries, not just pharmaceuticals. The brief explains that companies routinely make difficult choices among competing research projects and that liability for not commercializing marginal safety improvements quickly enough would distort investment priorities, slow development, and ultimately reduce consumer access to innovative products.

Trade & Civil Justice Groups:

• U.S. Chamber of Commerce, Washington Legal Foundation, California Chamber of Commerce, National Retail Federation
  • These groups explain that a new duty to commercialize alternative products would impose liability for commercially prudent decisions and force businesses to defend the order in which they develop and launch products. The brief warns that such a rule would be unworkable for companies and courts, increase litigation costs, and harm consumers by discouraging product improvement and raising prices.
• Product Liability Advisory Council
  • The Product Liability Advisory Council places the case in the broader history of products liability law, showing that proof of a product defect has always been central to negligence and strict liability claims involving product-caused injuries. The brief explains that the Court of Appeal’s “ordinary negligence” approach would create an end-run around established protections for prescription drug development and expand liability beyond administrable limits.
• National Association of Manufacturers, Alliance for Automotive Innovation, American Tort Reform Association, American Coatings Association, American Chemistry Council, Consumer Technology Association, Medical Device Manufacturers Association
  • These trade associations representing American business explain that the Court of Appeal’s new duty would affect far more than pharmaceuticals. The brief cautions that imposing liability for failing to develop or commercialize different product alternatives would invite speculative lawsuits, undermine predictable product liability standards, raise prices, and discourage safety-related innovation across manufacturing sectors.
• PhRMA, BIO, California Life Sciences
  • These life-sciences-focused groups provide a detailed account of the drug development process, emphasizing that early-stage clinical studies are limited and cannot support definitive conclusions about comparative safety or efficacy. The brief explains that imposing tort liability based on preliminary development decisions would misunderstand FDA-regulated research, deter investment in new medicines, and penalize companies for the inherent uncertainty of pharmaceutical innovation.
• Civil Justice Association of California, California Manufacturers & Technology Association, California Business Roundtable, Bay Area Council, BioCom
  • These California business and life sciences organizations urge the Court to reject the Court of Appeal’s reliance on California Civil Code section 1714 as a basis for creating a broad presumption of negligence duty. The brief warns that using section 1714 to override settled limits on tort liability would reduce predictability for California businesses and create uncertainty for manufacturers, innovators, and life sciences companies.

Academics/Experts:

• Pacific Research Institute
  • The Pacific Research Institute, in a brief authored by law professor and legal scholar Richard Epstein, explains that Gilead had no generalized duty to expedite TAF as a hypothetically safer alternative to TDF, particularly where TDF remained FDA-approved, adequately warned, and beneficial to patients. The brief states that plaintiffs’ theory rests on an incorrect account of both tort duty and the medical comparison between TDF and TAF, and that judicially second-guessing drug development timelines would undermine innovation and patient access.
• International Center for Law & Economics
  • The International Center for Law & Economics explains that the Court of Appeal’s rule would create potentially unlimited liability untethered to any defect in the product used by plaintiffs. The brief focuses on innovation incentives, explaining that pharmaceutical development is costly, uncertain, and already structured to encourage companies to bring promising products to market when science supports doing so.
• Atlantic Legal Foundation
  • The Atlantic Legal Foundation explains that imposing liability for pausing or delaying development of a potential drug candidate conflicts with the scientific method and the realities of pharmaceutical research. The brief emphasizes that early-stage testing cannot establish that a drug is safer or equally effective, and the brief warns that hindsight-based liability would discourage companies from pursuing beneficial drug development.
• International Association of Defense Counsel
  • The International Association of Defense Counsel urges the California Supreme Court to reverse the Court of Appeal and reaffirm that plaintiffs asserting products-liability claims must prove that the product at issue was defective. The brief explains that creating a duty to develop and commercialize an alternative to a non-defective product would disrupt settled products-liability law, chill innovation, increase prices, and expose manufacturers across industries to open-ended liability.
• Defense Research Institute, Association of Defense Counsel of Northern California and Nevada, Association of Southern California Defense Counsel
  • These organizations urge the California Supreme Court to reject the Court of Appeal’s new duty. The brief argues that imposing liability for failing to develop and market a different product sooner would be unprecedented, unworkable, and unpredictable, with consequences for pharmaceutical development and product innovation more broadly.

In March 2024, in support of Gilead’s petition for review by the California Supreme Court, 14 separate amicus letters, representing 50 signatories, were filed.

Over the course of the litigation, editorial boards, legal scholars and public health experts have weighed in on the adverse implications of this new legal theory. These include:

• 8/18/2023: The Wall Street Journal: A Most Bizarre Legal Theory, Editorial Board
  • The Wall Street Journal Editorial Board states that the litigation against Gilead advances a novel theory that companies can be sued not for selling a defective product, but for allegedly failing to launch a later product sooner. The editorial suggests that if plaintiffs prevail, companies across industries could be discouraged from researching improvements to existing products because early-stage experimentation could create future liability.
• 8/22/2023: American Action Forum’s The Daily Dish: A Defective Lawsuit, Douglas Holtz- Eakin
  • Douglas Holtz-Eakin – President of the American Action Forum – writes that the Gilead litigation reframes a dispute over drug development timing as a products-liability claim, despite both medicines having been approved by the FDA. He argues the theory could undermine incentives for pharmaceutical companies to improve existing products and could extend beyond medicines to other innovative industries.
• 8/24/2023: RealClear Health: Too Fast or Too Slow: Ambivalence about Drug Development Affects Health, Kirsten Axelsen
  • Kirsten Axelsen – a visiting scholar with the American Enterprise Institute – examines how legal, policy, and reimbursement decisions can affect investment in clinical development. She shows that penalizing companies for moving “too slowly” on next-generation medicines could make already risky drug development less attractive, particularly for conditions where treatments already exist.
• 9/19/2023: Law360: HIV Drug Case Against Gilead Threatens Medical Innovation, James Stansel
  • James Stansel – Executive Vice President, Law & Regulatory and General Counsel at PhRMA – explains that plaintiffs are advancing a novel theory that would impose liability on manufacturers for not developing a different product quickly enough, even when the product that patients used was not defective. He makes clear that applying this theory to FDA-approved HIV medicines would undermine the iterative nature of biopharmaceutical research, expose innovators to hindsight-based liability, and ultimately discourage the development of new treatments that benefit patients.
• 1/5/2024: Bio.News: BIO says suit over speed of drug development is threat to innovation and new cures
  • Bio.News summarizes BIO’s concerns that the plaintiffs’ theory could expose biopharmaceutical innovators to liability for not developing medicines sooner, and that such a precedent could discourage companies from pursuing scientific research and medical breakthroughs.
• 1/14/2024: The Wall Street Journal: California Invents a Crazy New Tort, Editorial Board
  • The Wall Street Journal Editorial Board criticizes the California appellate court ruling as creating a new standard under which companies could be sued for allegedly failing to develop improved products. The editorial explains this approach would create a Catch-22 for innovators: rushing products to market could invite liability, while taking time to study and develop them could also lead to lawsuits.
• 2/6/24: Law360: Gilead Ruling Signals That Innovating Can Lead To Liability, Gary Myers
  • Gary Myers – the Earl F. Nelson Professor of Law and a former dean at the University of Missouri School of Law – analyzes the California Court of Appeal decision as a potential expansion of products-liability law, warning that it could impose negligence liability based on the timing of product improvements. He explains that the ruling risks chilling innovation by allowing juries to second-guess complex research and development decisions with the benefit of hindsight.
• 2/13/2024: STAT News: A California court is setting a dangerous precedent over drug development (or lack thereof) liability, Dan Troy
  • Dan Troy – former Chief Counsel for the U.S. Food and Drug Administration – explains that the California appellate decision misunderstands how pharmaceutical companies make complex, resource-constrained R&D decisions. He warns that allowing plaintiffs to second-guess drug development choices years later could create a new avenue of litigation against companies for failing to advance one potential medicine over another, even where the existing medicine remains FDA-approved and available.
• 2/14/2024: Bloomberg Law: California’s Negligence Tort Empowers Juries, Hurts Innovation, George Priest
  • George Priest – a Yale law professor – explains that the California appellate ruling radically expands negligence law by allowing liability based on a company’s alleged failure to bring a later, purportedly superior product to market sooner. He states that the decision would shift product-development timing decisions from companies, regulators, and markets to lay juries, deterring innovation, increasing prices, and affecting industries beyond pharmaceuticals.
• 2/16/2024: Orange County Register How legal adventurism stifles medical innovation, Richard Epstein
  • Richard Epstein – the Laurence A. Tisch Professor of Law at NYU – writes that the Gilead ruling rests on a factually and legally flawed theory that ignores the uncertainty, cost, and complexity of securing FDA approval for new medicines. He warns that the decision could create indeterminate liability for companies that continue selling safe and effective products while developing alternatives, ultimately reducing medical innovation and patient choice.
• 3/4/2024: Law.com: How a Recent California Appellate Court Decision Will Chill Drug Development, Raise Pharmaceutical Costs, Jeremy Kidd
  • Jeremy Kidd – professor of law at Drake University – explains that the California appellate decision could punish pharmaceutical companies for bringing an FDA-approved drug to market before developing a later version with fewer side effects. He writes on how the ruling would raise the cost and risk of drug development, discourage companies from pursuing follow-on improvements, and create incentives to delay or avoid innovation rather than face hindsight-based liability.
• 3/14/2024: RealClear Health: Do Not Penalize Scientific Curiosity, Investigation, Kirsten Axelsen
  • Kirsten Axelsen – a visiting scholar with the American Enterprise Institute – explains that drug developers routinely make difficult choices about which scientific leads to pursue, pause, or abandon because resources are finite and failure is common. She says that imposing liability for not developing a potential medicine quickly enough would discourage scientific investigation and make companies less willing to explore possible future treatments.
• 3/19/2024: Forbes: Lawsuit Against Drug Company Could Quash Future Cures, Sally Pipes
  • Sally Pipes – President and CEO of the Pacific Research Institute – writes that the lawsuits against Gilead could discourage companies from trying to develop safer or more effective products if those efforts later become a basis for liability.
• 4/18/2024: A California court's liability pretzel logic will hurt patients, Peter Pitts
  • Peter Pitts – former Associate Commissioner of the U.S. Food and Drug Administration – explains that the California appellate court’s ruling turns products-liability law on its head by allowing claims based on the alleged failure to bring a different product to market faster, rather than on a defect in the product sold. He warns that the precedent could lead companies to experiment less, resulting in fewer medical breakthroughs for patients.
• 5/2/2026: VC Star: A lawsuit that may kill tomorrow's cures, Sally Pipes
  • Sally Pipes – President and CEO of the Pacific Research Institute – writes that plaintiffs’ theory would punish Gilead for not developing TAF quickly enough, even though they do not allege that TDF failed to work, was defectively manufactured, or lacked adequate warnings.
• 5/4/2026: Forbes: Can You Sue A Drug Company For Not Inventing Faster?, Sally Pipes
  • Sally Pipes – President and CEO of the Pacific Research Institute – explains that the California Supreme Court case raises a novel and potentially far-reaching question: whether a pharmaceutical company can face liability not for selling a defective drug, but for allegedly failing to develop a different drug faster. She warns that allowing courts to second-guess drug development timelines with hindsight could discourage investment in high-risk research, distort incentives for follow-on innovation, and ultimately reduce the number of new treatments available to patients.
• 5/5/2026: The Wall Street Journal: The Lawsuits Will Continue Until Morale Improves, Cory L. Andrews
  • Cory L. Andrews – General Counsel & Vice President of Litigation for the Washington Legal Foundation – explains that the California Court of Appeal’s ruling created a new tort based on alleged failure to innovate fast enough, departing from traditional products liability requirements focused on defects or inadequate warnings. Andrews warns that if the ruling stands, manufacturers could face hindsight-based liability for R&D decisions, leading companies to rush incomplete products, avoid high-risk research, abandon incremental improvements, or raise prices to account for unpredictable litigation risk.

FAQs about the litigation in the California Supreme Court

What is the TDF litigation?
This litigation, which is pending in the state courts of California, involves lawsuits over Gilead’s FDA-approved HIV medicines containing tenofovir disoproxil fumarate (TDF). Plaintiffs are individuals who took TDF-based medicines and claim that Gilead should have developed more quickly and sold sooner tenofovir alafenamide (TAF) based medicines.

Are these plaintiffs alleging that TDF medicines are defective?
No. Plaintiffs do not allege that the TDF medicines they took are defective. Rather, they argue only that Gilead should have continued developing TAF and made TAF-based medicines available sooner.

What legal issue is before the California Supreme Court?
The California Supreme Court is reviewing whether California law creates liability for a manufacturer based on a theory that the manufacturer should have researched, developed, and commercialized a different product that is an alternative to the manufacturer’s existing, non-defective product.

What is Gilead's position in the litigation?
Gilead disputes plaintiffs' legal and factual allegations in this case. As to the legal matter that is before the California Supreme Court, Gilead has explained that California law does not impose a duty on a manufacturer to develop and market a different product when its existing product is not defective. In addition, Gilead has shown that the long-term safety profile of TAF was unknown when development was halted in 2004.

What are TDF and TAF?
TDF and TAF are different forms of tenofovir that have been developed by Gilead and used in FDA-approved medicines to treat and prevent HIV.

Why did Gilead stop developing TAF in 2004 and resume development in 2010?
In 2004, consistent with FDA guidance and requests from the patient community, Gilead chose to focus its resources on developing groundbreaking combination and once-a-day, single pill treatments based on TDF.

At the time, TDF had already been on the market for years and had a proven safety and effectiveness profile. At the same time, the long-term safety of TAF-based medicines was still unknown and impossible to predict.

In the years that followed Gilead developed three different single-tablet regimens based on TDF.

In 2010, Gilead started studying TAF again as a possible additional treatment option for the aging population of individuals taking HIV medicines. It then took five more years of clinical trials and additional research to demonstrate the safety and effectiveness of TAF to obtain FDA approval to start selling TAF-based medicines.

Gilead is proud of its legacy combatting HIV, including its development of TDF- and TAF-based medicines to treat and prevent HIV. Both TDF- and TAF-containing medicines remain approved by the FDA, are recommended in the U.S. Department of Health and Human Services HIV treatment guidelines, and continue to help millions treat and prevent HIV.

Are TDF- and TAF-based medicines approved by the FDA?
Yes. Today, both TDF- and TAF-containing medicines remain approved by FDA as safe and effective treatment and prevention options for healthcare providers to meet the specific needs of people living with HIV. These medicines continue to successfully treat and prevent HIV in millions of people, and the Department of Health and Human Services lists both TDF and TAF as recommended therapies for HIV treatment and prevention.