Lilly starts a Phase 2 obesity trial of the selective GIP agonist macupatide

Eli Lilly and Company has started a Phase 2 trial of macupatide, an experimental obesity drug that targets only the GIP receptor, one of the two hormone pathways used by tirzepatide (sold as Mounjaro and Zepbound) ^[1]. The trial, listed as NCT07589608, began on May 15, 2026, in the United States and is testing macupatide both as a standalone treatment and in combination with other therapies for obesity ^[1]. This is the first Phase 2 obesity study for this molecule.

Macupatide, also known by the code names LAGIPRA and LY 3532226, is classified by Lilly's own development records as a new molecular entity, meaning it is a chemically distinct drug rather than a variation of an existing one ^[1]. Its listed mechanism of action is gastric inhibitory polypeptide (GIP) receptor agonism, which sets it apart from tirzepatide, which activates both the GIP and GLP-1 receptors, and from semaglutide products like Ozempic, Wegovy, and Rybelsus, which act only on the GLP-1 receptor ^[1].

Available development records show macupatide's highest development stage is now Phase 2 for both obesity and type 2 diabetes ^[1]. A separate program in type 1 diabetes has not shown recent movement, with the most recent update as of July 28, 2026, noting no reports of phase 1 development activity in the United States for that use ^[1]. Lilly is also expanding testing geographically: on August 14, 2026, the company outlined plans for a Phase 1 trial in Japan, expected to start in October 2026, that will look at macupatide alone and in combination for obesity (NCT07765511) ^[1].

The publicly available records do not include details on dosing, trial size, how long patients will be followed, or what results Lilly expects to measure, such as weight loss percentages or side effect rates. Those specifics are not yet known from the sources available.

Why it matters for patients

Most approved GLP-1 medicines for weight loss, including semaglutide and tirzepatide, work by activating GLP-1 receptors, GIP receptors, or both. Macupatide represents an attempt to test what a GIP-only approach can do on its own, separate from the GLP-1 effect that current drugs rely on ^[1]. Because tirzepatide combines both GIP and GLP-1 activity, isolating the GIP piece could help scientists and companies understand how much of tirzepatide's effect, and how much of its side effect profile, comes from each pathway.

For patients today, this development does not change anything about currently available treatments. Macupatide is in an early stage of testing, and Phase 2 trials are designed to explore dosing and gather more safety and effectiveness data before any larger studies would be needed. There is no information yet in these records about when, or whether, macupatide could become an approved medicine, what it might cost, or how it would compare to existing options.

What happens next

The Phase 2 obesity trial for macupatide in the United States began enrolling on May 15, 2026, under identifier NCT07589608 ^[1]. Separately, Lilly has outlined plans for a Phase 1 obesity trial of macupatide in Japan expected to begin in October 2026, registered as NCT07765511 ^[1]. As of the most recent update in these records, dated August 20, 2026, no additional trial results, safety data, or regulatory filings for macupatide have been reported ^[1]. Readers interested in tracking the drug's progress should watch for future updates on trial completion dates and any published results, none of which are yet available in current records.