Science1 publisher3 min readPublished
Lilly picked brenipatide's weekly dose from 212 volunteers enrolled by body mass index
A Phase I dose-selection study put brenipatide's half-life at 9 to 12.5 days. Lilly says that supports once-weekly dosing in the Phase III trials it is now running in major depressive disorder and alcohol use disorder.
The Scientist · Science desk
What happened
- Eli Lilly presented Phase I data on its GIP/GLP-1 agonist brenipatide supporting once-weekly dosing, and set out the design of Phase III trials in major depressive disorder and alcohol use disorder.
- The dose-finding study was investigator- and participant-blind, used multiple ascending doses, enrolled more than 200 people across three parts defined by body mass index, and followed them for eight weeks.
- Lilly's two marketed tirzepatide products earned $18.605 billion for Mounjaro and $9.088 billion for Zepbound in the first half of 2026, about 65% of the company's $42.773 billion in revenue.
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Why it matters
- constraint Nobody in this trial had depression or alcohol use disorder, so there is no efficacy signal in either indication to argue over; the Phase III commitment rests on receptor pharmacology and an exposure curve.
- decision Groups planning trials in recurrent major depression or alcohol use disorder now have to plan recruitment and comparator choice against a sponsor whose Phase III programme is already running.
- exposure Around two-thirds of Lilly's first-half revenue sits in two incretin products. Indication expansion outside metabolic disease is a route to new growth from the same modality.
- precedent Taking a dual incretin into psychiatry on safety and pharmacokinetics sets the pattern for how the class gets extended: receptor rationale and dosing convenience first, behavioural endpoints afterwards.
Add the three parts and the trial randomized 212 people: 108 in Part A at BMI 27.0 to 45.0, 72 in Part B at 22.0 to 26.9, and 32 in Part C, also at 22.0 to 26.9 and limited to Japanese and Chinese participants [8][9][10][1]. Of those, 184 received brenipatide and 28 received placebo [2]. Four discontinuations out of 184 treated is 2.2%, the number Lilly reported; four out of 212 would be 1.9% [13][3]. The primary outcome was safety, measured by adverse events that investigators judged related to the study drug [12], and the most frequent treatment-emergent events were gastrointestinal [14].
Weekly dosing comes down to duration. Mean half-life ran from 9.08 days to 12.5 days, the longer figure at the top 4.5 mg dose [6], which puts elimination at roughly 1.3 to 1.8 times a seven-day interval [5]. Dose weekly into that and exposure accumulates. Part A participants on 4.5 mg reached a mean plasma concentration just over 1,000 ng/mL by Day 78 [11]. Robert Nicholson, an associate vice president for neuroscience medical affairs at Lilly, told GEN the profile "allows us to have a durability of exposure that can go beyond the weekly dosing interval" [16].
For neuroscience, the rationale sits at the receptor level. Unlike tirzepatide, brenipatide is designed to reach GIP and GLP-1 receptors in central nervous system and inflammatory pathways, including receptors linked to reward and addiction in the brain [3]. The Phase I population was healthy, overweight and obese volunteers enrolled by body mass index, and the measurements were safety, pharmacokinetics and pharmacodynamics [5].
Roughly half the study sat at normal to modestly overweight body mass: Parts B and C together enrolled 104 people at BMI 22.0 to 26.9, 49% of the 212 [4]. The design follows the indication. A patient with recurrent major depression is not selected for excess weight, so the dose has to be tolerable in someone with none to lose. Lilly's researchers concluded in the poster that the data "support the selection of weekly maintenance doses across a broad range of BMIs, including normal body weight, that optimize safety, tolerability, and incretin pharmacology" [17].
Metabolic products are paying for this. Mounjaro and Zepbound brought Lilly $18.605 billion and $9.088 billion in the first six months of 2026, $27.693 billion together, about 65% of the company's $42.773 billion in revenue over that period [15][6]. Nicholson said: "Having that longer half-life is some of the reason why we think there's a distinct profile for brenipatide relative to currently available incretin therapies" [18]. He said the Phase III trials in alcohol use disorder and recurrent major depressive disorder are under way now [19]. Lilly has not given a readout date for either [20].
What to watch
- Full publication of the poster data, including the overall gastrointestinal event rate and any weight change in the normal-BMI parts.
- The registered primary endpoints for the alcohol use disorder and recurrent major depressive disorder Phase III trials, and how they handle weight loss as a confound.
- Whether regulators accept a BMI-selected volunteer population as adequate dose justification for central nervous system indications.