Nearly 600 postmarket studies that makers of drugs and biologics were required to perform, or had promised to perform, were running behind schedule as of August, a KFF Health News analysis of FDA data found. The delayed studies involve almost 350 products, many of which remain available while the research meant to answer open safety or effectiveness questions is unfinished.
For patients, that means some medicines are being prescribed without all of the evidence regulators asked for when they approved them. Federal health officials stress that a delay does not by itself mean a product is unsafe, but it can leave doctors and patients making decisions with incomplete information.
More than 250 of the delayed studies originally had final reports due before July 31, 2026, and about a third of ongoing studies in the database were listed as delayed, the analysis found. Separate FDA databases for medical devices listed dozens more studies as behind schedule.
Approval Now, Evidence Later
To move treatments to patients faster, the FDA can approve a product while requiring the manufacturer to complete more research after it reaches the market. Some postmarket studies are mandatory requirements, and others are commitments a company agrees to. Products cleared through accelerated approval must also confirm that they deliver real clinical benefit.
The word delayed has a specific meaning. The FDA defines a delayed study as one behind its original schedule, which can mean a study that is off track or one that is already overdue. In some cases, the agency has granted extensions, and in others it has denied them.
The Department of Health and Human Services, which oversees the FDA, said delays can happen for legitimate reasons. "Assessing the significance of any delay requires a case-specific review," HHS spokesperson Emily Hilliard told KFF Health News. She added that a delay should not be treated as evidence of an unresolved safety or effectiveness issue and said the FDA uses its enforcement powers where appropriate.
Cases That Show What Is at Stake
The vasculitis drug Tavneos, approved in 2021, came with a required safety study of 300 patients, each to be followed for five years. As of July 24, only 49 patients had been enrolled, according to its maker, Amgen. The FDA has cited 76 cases of drug-induced liver injury and has proposed withdrawing the drug's approval.
The FDA also alleges that results from a trial used to support approval were manipulated, a claim Amgen denies. The company says the drug's benefits outweigh its risks, and Tavneos remains on the U.S. market while the dispute continues. The European Union has revoked its approval of the drug, which can cost more than $220,000 a year. Amgen estimates U.S. real-world use at more than 6,500 patient-years.
Other examples involve very different patients. A study of the COVID-19 treatment Paxlovid in pregnant women missed its completion and final report milestones, and Pfizer says it remains committed to submitting results. A pediatric study of the CustomFlex Artificial Iris had enrolled no patients, while a study of the Scandinavian Total Ankle Replacement system that planned for at least 500 patients had enrolled 142.
The Duchenne muscular dystrophy drug Exondys 51 had a final report due in May 2021 that is still listed as delayed. Its maker, Sarepta Therapeutics, says the study has been fully enrolled since 2023 and plans to share initial data late this year. Companies often cite small patient populations, reluctance to risk receiving a placebo when an approved drug already exists, and competition from other trials as reasons for slow recruitment.
Taxpayers and Patients Share the Cost of Waiting
Delays can be costly for public programs. Medicare and Medicaid spent more than $18 billion from 2018 to 2021 on accelerated approval drugs whose confirmatory trials were past their planned completion dates, the HHS Office of Inspector General estimated in 2022.
Researchers worry the stakes are rising. In February, FDA leaders announced in the New England Journal of Medicine that one pivotal clinical trial, rather than two, would become the default requirement for approvals. Harvard Medical School professor Aaron Kesselheim told KFF Health News that reducing pre-approval testing will put more pressure on follow-up research. FDA officials have said the change will not compromise safety or effectiveness.
People with rare diseases may be most affected, since small patient populations make recruitment hard and approved alternatives are few. Pregnant patients, children, and people taking costly specialty drugs also depend on evidence that is still being gathered.
Anyone can search the FDA's postmarket requirements and commitments database by drug name to see a study's status. Patients can ask a prescriber whether a medicine received accelerated approval, whether follow-up studies are complete, and what monitoring is recommended. Suspected side effects can be reported to the FDA's MedWatch program.
Patients taking Tavneos should talk with their clinician about liver monitoring and report symptoms such as yellowing skin or eyes, dark urine, unusual fatigue, or itching. No one should stop a prescribed medicine without first speaking with a qualified clinician, because abrupt changes can carry risks of their own.
The FDA has not said which delayed studies it considers most concerning, and the database does not rank them by risk. The Tavneos withdrawal proceedings and Sarepta's expected data release are the next milestones to watch.
Key Questions Answered
What did the KFF Health News analysis find? Nearly 600 postmarket studies of drugs and biologics that the FDA required or that companies agreed to perform were behind schedule as of August, involving almost 350 products.
Does delayed mean a study is overdue? Not always. The FDA defines delayed as behind the original schedule, which can mean off track or overdue.
Are products with delayed studies unsafe? A delay alone does not prove a product is unsafe. HHS says each delay needs case-specific review, but delays can leave questions about risks and benefits unanswered.
How did HHS respond? HHS spokesperson Emily Hilliard said delays can happen for legitimate reasons and should not be treated as evidence of an unresolved safety or effectiveness issue.
How can I check a medicine's study status? Search the FDA's postmarket requirements and commitments database by drug name, and ask your prescriber whether follow-up studies are complete.
Should I stop a medicine that has a delayed study? No. Do not stop or change any prescribed medication without talking with a qualified clinician first.
