FDA-Ordered Studies Stall Years After Drugs Hit Market, Raising Safety Questions

The FDA has hundreds of drug and device safety studies running behind schedule, a structural flaw that the Trump administration is about to make worse, creating a compliance and liability overhang that institutional capital in healthcare has not priced.

A KFF Health News analysis published September 18, 2026, found nearly 600 postmarket studies in the FDA's drug and biologics database listed as delayed . More than 250 of those studies had final reports originally due before July 31, 2026. Roughly one-third of all ongoing studies in the database carried a delayed designation. The nearly 600 delayed studies span almost 350 distinct products, meaning the problem is not concentrated in a handful of bad actors but distributed across the industry's approved portfolio.

"Doctors rely on this evidence, patients rely on this evidence, and if that evidence is not there, it's going to lead to a lot of uncertainty," said Sanket Dhruva, a cardiologist and associate professor of medicine at the University of California-San Francisco who has published research on postmarket requirements .

The nut of the problem is structural. The FDA routinely approves drugs and devices with unresolved safety questions, then mandates postmarket studies to fill the evidentiary gaps. When those studies stall, the regulatory bargain breaks down. Patients and payers absorb the risk. Manufacturers collect revenue. The gap between approval and evidence completion has proven, in Dhruva's words, "toothless" for years . Now, with the Trump administration compressing pre-approval testing requirements, the postmarket system will carry even more weight, on a foundation that the data show is already cracking.

Tavneos: A Case Study in the Cost of Delayed Evidence

Amgen's Tavneos, approved by the FDA in 2021 to treat rare autoimmune diseases, illustrates the mechanics of the problem. FDA reviewers at the time of approval flagged limited safety data as a concern. The agency approved the drug anyway, conditioning that approval on a years-long postmarket safety study .

As of an FDA letter issued in April 2026, only 21 of the planned 300 patients had been enrolled in that study. The FDA has since identified dozens of cases of liver damage described as possibly or probably causally associated with Tavneos, precisely the kind of safety signal the postmarket study was designed to investigate .

Amgen spokesperson Alison Chartan confirmed the company is still working on the mandated research and said the company remains committed to completing the study . Terms of any FDA enforcement action or timeline extension were not disclosed in the source material.

The Tavneos enrollment figure, 21 patients out of 300 planned, implies a completion rate of 7% on a study that was conditioned on approval granted five years ago. At that pace, the study is not a near-term catalyst, it is a long-duration liability sitting on the balance sheet of every investor who holds Amgen without modeling the regulatory risk.

The CustomFlex Artificial Iris and the Device Side of the Ledger

The drug database does not carry the full picture. Separate FDA databases tracking medical devices listed additional postmarket studies as behind schedule as of August 2026 . Among them: the CustomFlex Artificial Iris, a prosthetic implanted to replace damaged or congenitally missing irises. The FDA accepted the protocol for a pediatric study in 2019. The study was designed to follow patients for five years. As of the August download, zero patients had been enrolled .

Barbara Fant of Clinical Research Consultants, the contact named in the FDA's 2018 approval letter for the product, said the rarity of aniridia, the eye disease the device addresses, creates enrollment challenges. Fant noted that the German manufacturer, the U.S. distributor, and Clinical Research Consultants are working with the FDA on alternative approaches to fulfilling postmarket requirements . The FDA has not publicly disclosed whether it will accept those alternatives or what timeline applies.

For PE buyers underwriting orphan device assets, the CustomFlex situation is a template for a recurring due diligence gap: rare disease products often carry the longest postmarket study commitments and the least feasible enrollment pathways, a combination that creates regulatory exposure with no clear resolution timeline.

Trump's One-Trial Rule Shifts Risk Downstream

On February 2026, FDA leadership announced that the default requirement for new drug approvals would shift from two clinical trials to one . FDA officials writing in The New England Journal of Medicine argued the change would not compromise safety or efficacy, citing the argument that erroneous conclusions can emerge even from two, three, or four studies . The agency said the policy would substantially reduce costs for manufacturers and accelerate market access .

Aaron Kesselheim, a professor at Harvard Medical School who has analyzed postmarket studies, told KFF Health News that reducing pre-approval testing will inevitably put significant pressure on the post-approval system . That pressure lands on a system that, by the FDA's own data, already cannot clear its existing queue.

The policy arithmetic is unfavorable. If the pre-approval evidentiary standard drops and postmarket compliance rates stay flat or deteriorate, the information deficit for drugs entering the market in 2026 and beyond will be larger than for the cohort currently generating delayed study flags. Institutional investors pricing pipeline assets or underwriting pharma platform deals need to treat this as a baseline assumption, not a tail risk.

Separately, on September 18, 2026, President Trump announced that all 50 states, Washington, D.C., and Puerto Rico would participate in the GENEROUS model, a Medicaid drug discount program designed to lower drug prices for state programs . The Centers for Medicare and Medicaid Services clarified that 40 states and Puerto Rico had signed agreements, with others still in application, and that states had until the end of September to finalize . Deal terms and per-drug discount structures were not made public in the available source material.

The GENEROUS announcement adds another pricing variable to the pharma revenue calculus. Lower Medicaid reimbursement rates, combined with a regulatory framework that front-loads commercial revenue before safety studies are complete, creates a specific risk profile: compressed margins on the back end, unknown liability on the safety side.

Enforcement: Rare, and Getting Rarer

The FDA's own data show a spectrum of responses to delayed studies. The agency has granted extensions in some cases, denied them in others, and in rare instances, products were withdrawn before studies concluded . An HHS spokesperson, Emily Hilliard, said in response to KFF Health News questions that delays can occur for legitimate reasons and that a delayed study should not be treated as evidence of an unresolved safety issue, adding that any assessment requires case-specific review .

That framing is consistent with an enforcement posture that has historically stopped well short of withdrawal or financial penalty. For manufacturers, the expected cost of non-compliance with postmarket study timelines has been low. For investors, that means the liability is not priced into current multiples because it has rarely materialized as a hard financial event. The question is whether the Trump-era deregulatory push changes that calculus in either direction, fewer studies required up front, but potentially sharper political scrutiny when safety signals emerge post-approval.

The Plocamium View

The market treats FDA postmarket study delays as a compliance footnote. Plocamium reads them as a leading indicator of platform-level due diligence failure in healthcare M&A.

Here is the thesis the source articles do not make: the combination of the one-trial approval default and the existing postmarket backlog creates a two-stage liability cliff for any PE sponsor underwriting a pharma or specialty device platform over a five-to-ten-year hold. Stage one is commercial, revenues accrue while studies remain incomplete and reimbursement is intact. Stage two is the inflection, when a safety signal accumulates to the point that it forces label changes, reimbursement restrictions, or withdrawal. The Tavneos liver damage signal is an early-stage example of stage two dynamics beginning to surface.

For buyers assembling rare disease or specialty pharma platforms, the postmarket study register is a credit document, not a compliance checkbox. A product with a 7% enrollment rate on a mandated safety study five years post-approval is not a clean asset. It is an asset with an open regulatory liability that will either resolve favorably or become the lead paragraph of an adverse event disclosure.

The GENEROUS Medicaid discount program adds a second vector. If 40-plus states are locking in lower Medicaid pricing for drugs that are still completing their postmarket safety evidence, the revenue runway for those products may be shorter and the per-unit margin lower than the underwriting models assume. That compression hits hardest in rare disease, where Medicaid and government programs represent an outsized share of the payer mix.

The second-order play: firms that build proprietary postmarket study compliance analytics, mapping enrollment rates, FDA extension histories, and safety signal accumulation against approved product portfolios, will have a structural edge in pharma platform diligence. That capability does not yet exist as a standalone product in the market. The data to build it is public.

The Bottom Line

The FDA's postmarket study system is running a disclosed, quantified backlog of nearly 600 delayed studies across almost 350 products, with a regulatory administration that is simultaneously reducing the pre-approval evidence standard. The result is more drugs reaching patients with less pre-market data, backstopped by a follow-up system that has already demonstrated it cannot close its existing queue.

For institutional capital, the actionable framing is this: any healthcare M&A transaction that includes assets with open postmarket study obligations requires a study-specific compliance review as a condition of underwriting, not a post-close integration item. The Tavneos enrollment figure and the CustomFlex zero-patient enrollment are not outliers. They are the norm. Price accordingly.