The Lancet issues an Expression of Concern on the exenatide Parkinson's trial

The Lancet has published an Expression of Concern about a 2025 clinical trial that tested exenatide, a GLP-1 receptor agonist, as a potential disease-modifying treatment for Parkinson's disease ^[1]. An Expression of Concern is a formal notice from a journal's editors that something about a published paper needs further review; it is not the same as a retraction, and the underlying study has not been withdrawn ^[1].

The paper in question, "Exenatide once a week versus placebo as a potential disease-modifying treatment for people with Parkinson's disease in the UK," was a phase 3, multicentre, double-blind, parallel-group, randomised, placebo-controlled trial led by N. Vijiaratnam and colleagues ^[1]. It was published in The Lancet on February 22, 2025, in volume 405, issue 10479, pages 627 to 636, after being posted online on February 4, 2025 ^[1]. The PubMed record for the original study carries the identifier PMID 39919773 ^[1]. The new Expression of Concern is listed as a separate publication tied to that paper, under PMID 42330995 ^[1].

The PubMed listing for the Expression of Concern does not include an abstract explaining the specific reasons the editors are reviewing the trial ^[1]. That means the exact nature of the concern — whether it involves the data, the statistical analysis, the conduct of the trial, or something else — is not stated in the available record and is not yet known from the sources reviewed here.

Exenatide is an older GLP-1 receptor agonist, sold under brand names such as Byetta and Bydureon, and it is a different molecule from semaglutide (sold as Ozempic, Wegovy, and Rybelsus) and tirzepatide (sold as Mounjaro and Zepbound) ^[1]. The flagged trial did not test semaglutide or tirzepatide. But because exenatide belongs to the same broad drug class that includes those medicines, the dispute touches on a question of wide interest: whether GLP-1 drugs can slow or modify the course of Parkinson's disease, not just treat diabetes or obesity.

Why it matters for patients

For people who take semaglutide or tirzepatide for diabetes or weight management, this development does not change anything about the safety or effectiveness of those specific drugs for their approved uses. The concern is narrowly about a separate trial of a different GLP-1 drug, exenatide, in Parkinson's disease ^[1].

For patients or caregivers who have seen reports describing exenatide, or GLP-1 drugs generally, as possibly slowing Parkinson's disease progression, the Expression of Concern is a signal that those specific findings are now unsettled ^[1]. Any news coverage, medical discussion, or online claim that cites the 2025 Exenatide-PD3 results as evidence that GLP-1 drugs modify Parkinson's disease should be read with that caveat in mind until the journal resolves the matter ^[1].

It is also worth noting what an Expression of Concern is not. It is not a finding of fraud or misconduct, and it is not proof the trial's conclusions are wrong. It is a formal pause, signaling that editors want more scrutiny before the paper's claims can be relied upon as settled science ^[1].

What happens next

The sources reviewed do not specify a timeline for when The Lancet will complete its review or what outcome might follow, such as a correction, an author response, or a retraction. As of the most recent record available, the original 2025 paper remains published and has not been retracted, and the Expression of Concern remains the most recent formal action taken by the journal ^[1]. Readers looking for updates should watch for further notices attached to the same PubMed record, PMID 39919773, or updates from The Lancet itself.