The FDA is fundamentally changing how it approves new drugs, moving away from a requirement that has shaped medicine for over six decades. Starting now, the agency will generally require only one adequate and well-controlled clinical trial supported by confirmatory evidence, rather than the traditional two pivotal studies that have been the default standard since the 1960s . This marks one of the most significant regulatory policy shifts in recent decades and reflects the FDA's broader effort to accelerate patient access to new treatments.

Why Did the FDA Keep the Two-Trial Rule for So Long?

The two-study requirement emerged from Congress's 1960s mandate for "adequate and well-controlled investigations" before drug approval. For decades, the FDA interpreted this language as requiring at least two independent studies, a safeguard designed to reduce the risk that a single positive trial was simply a statistical fluke rather than proof that a drug actually works . From a statistical standpoint, requiring two trials meant a pharmaceutical company had to demonstrate success more than once, making it much harder for a false positive to slip through.

However, FDA Commissioner Marty Makary and FDA vaccine chief Vinay Prasad argued in a policy article published in the New England Journal of Medicine that advances in biology, trial methodology, and statistical science now justify moving away from this long-standing expectation . "In 2026 there are powerful alternative ways to feel assured that our products help people live longer or better than requiring manufacturers to test them yet again," they wrote .

Vinay Prasad

What Evidence Will Replace the Second Trial?

The FDA has actually had statutory authority since 1997 to approve drugs based on a single adequate and well-controlled study combined with confirmatory evidence, but this flexibility was rarely used for common conditions . Now, the agency is formalizing a broader approach to what counts as "confirmatory evidence." This can include mechanistic data showing how a drug works at the biological level, results in related disease indications, animal models, class effects showing that similar drugs work the same way, or real-world evidence from actual patient use .

Rather than focusing on the number of trials, FDA reviewers will now concentrate on trial quality parameters, including the magnitude of effect, appropriateness of control arms, endpoint selection, statistical power, blinding, handling of missing data, biological plausibility, and alignment with intermediate biomarkers . In other words, one exceptionally well-designed study with strong supporting evidence may now carry more weight than two poorly designed trials.

How to Understand the New FDA Approval Standards

• Trial Quality Over Quantity: The FDA will prioritize the rigor and design of a single study rather than automatically requiring duplication, meaning reviewers will examine effect size, control group appropriateness, and statistical power more carefully.
• Biological Plausibility: Modern drug development rarely involves testing biologically implausible compounds; therapies are typically supported by detailed mechanistic science and biomarker data that can corroborate efficacy without a second trial.
• Multiple Forms of Evidence: Confirmatory evidence can now come from mechanistic studies, results in related indications, animal models, class effects, or real-world data, giving the FDA more flexibility in how it evaluates drug safety and effectiveness.

Which Drugs Will Be Most Affected by This Change?

The practical impact of this policy shift may be greatest for drugs treating common conditions that historically were held to the two-trial benchmark . Oncology and rare diseases have already operated under single-trial flexibility for years, so cancer drugs and treatments for uncommon illnesses will see less change. Dr. Janet Woodcock, who led the FDA's drug center for roughly two decades before retiring in 2024, explained the distinction: "It's not the cancers and the rare diseases that will be affected by this. The agency has been approving those on a single trial already" .

"The scientific point is well taken that as we move toward greater understanding of biology and disease we don't need to do two trials all the time," said Dr. Janet Woodcock.

Dr. Janet Woodcock, former director of FDA's drug center

This means drugs for conditions like heart disease, diabetes, arthritis, and other common ailments could potentially reach patients faster under the new framework, assuming they meet the FDA's stricter quality standards for a single trial.

What Do Critics Say About Weakening Standards?

Some observers worry that requiring only one trial could weaken the FDA's safety standards and allow less-proven drugs to reach patients. However, Makary and Prasad reject this criticism, arguing that two poorly designed trials do not guarantee valid conclusions . They contend that concentrating review resources on a single rigorous, well-designed study may actually strengthen regulatory scrutiny. "Without examination of the quality of a study, two trials may even provide a false assurance," they wrote .

They

The shift reflects a broader philosophy: that the FDA's job is not to count trials but to ensure that the evidence supporting a drug's approval is scientifically sound, biologically plausible, and robust enough to protect patients. By focusing on the quality and comprehensiveness of evidence rather than the number of studies, the agency aims to speed up drug development while maintaining safety standards.

Both officials expected the change would spur "a surge in drug development," potentially bringing new treatments to patients faster . The policy represents a significant departure from decades of regulatory practice, but one grounded in modern scientific understanding of how drugs work and how to evaluate their effectiveness.