A definitive phase 3 trial found that weekly exenatide injections did not slow Parkinson's disease progression over two years, despite earlier promising signals.
p=0.47No significant difference in Parkinson's motor progression between exenatide and placebo over 96 weeks — the drug did not modify disease course
What the researchers found
In this definitive phase 3 trial, the GLP-1 receptor agonist exenatide did NOT slow Parkinson's disease progression compared to placebo. After 96 weeks, Parkinson's motor symptoms worsened by 5.7 points in the exenatide group versus 4.5 points in the placebo group on the MDS-UPDRS III scale — no meaningful difference (p=0.47).
The drug was safe and well-tolerated, with serious adverse events actually slightly lower in the exenatide group (9% vs 11%). But the primary hypothesis — that exenatide could be a disease-modifying treatment for Parkinson's — was not supported by the data.
Why it matters
There had been enormous excitement about GLP-1 drugs potentially protecting the brain, fueled by lab studies showing neurotrophic properties and a smaller earlier trial suggesting benefits. This large, rigorous phase 3 trial is a reality check: exenatide does not appear to slow Parkinson's progression. It's an important negative result that redirects the field toward either different GLP-1 agents with better brain penetration or targeting specific patient subgroups who might still respond.
The numbers in context
n=194 · 96 weeks · MDS-UPDRS III OFF worsening: +5.7 (exenatide) vs +4.5 (placebo) · p=0.47 · Serious adverse events: 9% vs 11% · Exenatide 2 mg/week subcutaneous
How the study worked
Phase 3, multicentre, double-blind, parallel-group, randomised, placebo-controlled trial across 6 UK research hospitals. 194 participants with Parkinson's disease (Hoehn & Yahr stage ≤2.5, ages 25-80) were randomized 1:1 to exenatide 2 mg extended-release subcutaneous injection once weekly or placebo for 96 weeks. The primary outcome was change in MDS-UPDRS Part III motor score assessed while patients were off their dopaminergic medications, analyzed using intention-to-treat with linear mixed modeling.
Who was studied
194 adults (ages 25-80, 71% male) with Parkinson's disease at Hoehn & Yahr stage 2.5 or less, on stable dopaminergic treatment, across 6 UK research hospitals
What this study cannot tell us
The trial used exenatide, an older GLP-1 agonist that may have limited brain penetration compared to newer agents like semaglutide. The sample size (194) may have been underpowered to detect subtle effects or benefits in subgroups. The study enrolled participants relatively early in their disease course (Hoehn & Yahr ≤2.5). COVID-19 pandemic overlap may have affected follow-up and participation.
How to read the evidence
This is a well-designed phase 3, double-blind, randomized, placebo-controlled trial published in The Lancet — the gold standard for clinical evidence. The negative result is just as informative as a positive one.
When this study was published
Published in 2025 in The Lancet. This is the most current and definitive trial on exenatide for Parkinson's, superseding earlier positive signals from smaller studies.
The bigger picture
This is one of the most important negative results in the GLP-1/neurodegeneration field. With millions taking GLP-1 drugs for diabetes and weight loss, and epidemiological data suggesting lower Parkinson's risk in those populations, the hope was that these drugs could be repurposed for brain diseases. This trial shows it's not that simple — at least not with exenatide. The research community is now looking at newer GLP-1 agonists like lixisenatide and semaglutide, which may cross the blood-brain barrier more effectively.
Questions still open
- Would newer GLP-1 agonists like semaglutide, which may have better brain penetration, produce different results in Parkinson's disease?
- Are there specific genetic or clinical subgroups of Parkinson's patients who might still benefit from GLP-1 receptor activation?
- Do the epidemiological associations between GLP-1 drug use and reduced Parkinson's risk reflect something other than direct neuroprotection?
Common questions
Why did scientists think a diabetes drug might help Parkinson's disease?
Does this mean all GLP-1 drugs are useless for Parkinson's?
Read the original research
Exenatide once a week versus placebo as a potential disease-modifying treatment for people with Parkinson's disease in the UK: a phase 3, multicentre, double-blind, parallel-group, randomised, placebo-controlled trial.
Lancet (London, England), 405(10479), 627-636
Citation
Vijiaratnam, Nirosen; Girges, Christine; Auld, Grace; McComish, Rachel; King, Alexa; Skene, Simon S; Hibbert, Steve; Wong, Alan; Melander, Sabina; Gibson, Rachel; Matthews, Helen; Dickson, John; Carroll, Camille; Patrick, Abigail; Inches, Jemma; Silverdale, Monty; Blackledge, Bethan; Whiston, Jessica; Hu, Michele; Welch, Jessica; Duncan, Gordon; Power, Katie; Gallen, Sarah; Kerr, Jacqueline; Chaudhuri, K Ray; Batzu, Lucia; Rota, Silvia; Jabbari, Edwin; Morris, Huw; Limousin, Patricia; Greig, Nigel; Li, Yazhou; Libri, Vincenzo; Gandhi, Sonia; Athauda, Dilan; Chowdhury, Kashfia; Foltynie, Tom. (2025). Exenatide once a week versus placebo as a potential disease-modifying treatment for people with Parkinson's disease in the UK: a phase 3, multicentre, double-blind, parallel-group, randomised, placebo-controlled trial.. Lancet (London, England), 405(10479), 627-636. https://doi.org/10.1016/S0140-6736(24)02808-3