Eli Lilly presented data at the European Congress on Obesity in Istanbul today and published simultaneously in Nature Medicine the results of ATTAIN-MAINTAIN — a Phase 3b switch trial showing that patients who previously achieved weight loss on injectable Wegovy or Zepbound can transition to oral Foundayo (orforglipron) and maintain 78 to 82 percent of their prior weight loss over 52 weeks.

This is the first clinical trial in the obesity space demonstrating that patients can successfully switch from an injectable GLP-1 to an oral GLP-1 at maintenance doses without losing the bulk of their achieved weight loss. It repositions Foundayo’s competitive case from “the slower oral option” to “the maintenance bridge after injectables.”

What the Trial Tested

ATTAIN-MAINTAIN enrolled adults with obesity or overweight who had previously completed SURMOUNT-5 — Lilly’s head-to-head trial of injectable Zepbound versus injectable Wegovy. The participants entered ATTAIN-MAINTAIN already at a stable post-injectable weight loss.

Two cohorts, both 52 weeks, randomized, double-blind, placebo-controlled.

Cohort 1 — Wegovy → Foundayo. Patients previously on injectable semaglutide (Wegovy) switched to oral orforglipron at maintenance doses. At 52 weeks, the cohort had maintained all but 0.9 kg of previously achieved weight loss, equivalent to 82.4% maintenance.

Cohort 2 — Zepbound → Foundayo. Patients previously on injectable tirzepatide (Zepbound) switched to oral orforglipron. At 52 weeks, the cohort had maintained all but 5.0 kg of previously achieved weight loss, equivalent to 78.0% maintenance.

The placebo arms drifted upward over the 52 weeks, as expected. The active arms held.

Why the 78–82% Number Matters

The 78–82% maintenance range is not just impressive — it’s pharmacologically informative.

The asymmetry between the two cohorts (82.4% Wegovy-to-Foundayo, 78.0% Zepbound-to-Foundayo) reflects the underlying mechanism. Zepbound’s dual GLP-1/GIP agonism produces more weight loss at peak injectable dosing than Wegovy’s pure GLP-1 agonism. Switching to an oral pure-GLP-1 like Foundayo leaves more “uncovered” weight loss in the Zepbound cohort than in the Wegovy cohort. The maintenance percentage is anchored to the baseline. Tirzepatide patients are mechanically harder to maintain on Foundayo than semaglutide patients, because their baseline weight loss was higher to begin with. The data fits the pharmacology.

The clinical significance: patients who succeed on injectable Wegovy or Zepbound and want to step down from weekly subcutaneous injections — a clinically meaningful and growing patient population — now have data supporting an oral switch. The 78–82% maintenance figure is the first quantified answer to the most common patient question in GLP-1 communities: “Can I switch from injections to a pill?”

What This Reframes

Before ATTAIN-MAINTAIN, Foundayo’s competitive case was built around being the first FDA-approved small-molecule oral GLP-1, with no food or water dosing restrictions, but with lower per-dose efficacy than the injectables. The launch trajectory through the first month — roughly 7,000 weekly prescriptions by Week 4 IQVIA — looked modest against Novo’s Wegovy pill (1.3 million prescriptions in Q1 2026).

ATTAIN-MAINTAIN reframes the competitive question. Foundayo is no longer competing with Wegovy pill for first-line oral obesity prescribing. It is positioned as the maintenance solution for patients who succeeded on injectables and want to stop injecting. That is a structurally different addressable market — and one that grows over time as the injectable patient population continues to expand.

The data is also a trial Novo cannot run. Novo doesn’t have Foundayo. They have oral semaglutide (Rybelsus 14 mg, Wegovy pill 25 mg), but those are higher-dose oral formulations of the same molecule already present in the injectable. They are not structurally distinct small-molecule oral GLP-1s. ATTAIN-MAINTAIN is therefore a category-defining trial: the only trial demonstrating injectable-to-oral switch maintenance in the obesity space. Whatever Novo presents at the next congress, they cannot match this dataset on this specific question.

What the Trial Does Not Tell Us

Three honest limitations.

The trial enrolled SURMOUNT-5 completers — a pre-screened, treatment-experienced population that had already demonstrated tolerance to and response from injectable GLP-1 therapy. That is not the general patient population. Patients who never tolerated injectables (roughly 10–18% of starting populations in real-world data) are not represented in ATTAIN-MAINTAIN. The maintenance figure should be read as applying to patients who succeeded on an injectable and switched — not all patients switching.

The trial design did not include a continued-injectable comparator arm. The clinically operative question — “if I switch to Foundayo, will I keep most of my weight loss?” — is answered well. The relative question — “would I have kept more if I stayed on the injectable?” — is not. We don’t know whether continued injectable users would have maintained 95% rather than 78–82%, because that comparison wasn’t built into the trial.

The 52-week duration is sufficient to establish maintenance but does not address chronic-therapy questions. GLP-1 therapy is increasingly understood as a long-term intervention rather than a course of treatment. Five-year and ten-year maintenance data will eventually be the more clinically relevant question; 52-week data is the necessary first step.

What This Means

For patients currently on injectable Wegovy or Zepbound considering an oral switch: ATTAIN-MAINTAIN provides the clinical evidence base. The decision still depends on individual treatment goals, payer coverage, and clinical context — but the question of whether the switch is supported by evidence now has a clear answer. The orforglipron / Foundayo compound article walks through the full evidence base.

For the oral GLP-1 competitive landscape: the class is differentiating. Wegovy pill for de novo obesity. Foundayo for post-injectable maintenance. Viking’s VK2735 oral for future patients. The amylin agonist class (Pfizer PF-3944, Viking VK3019) for GLP-1-intolerant or GLP-1-non-responsive patients. Different therapies for different therapeutic moments.

For the Foundayo launch trajectory specifically: the next Week 5 and 6 IQVIA reports will reveal whether the ATTAIN-MAINTAIN data shifts prescribing patterns within the four-to-six-week window typical for prescriber-narrative-driven prescribing changes. If maintenance positioning expands the addressable prescriber population, the prescription curve should reflect it in the near-term commercial data.

References

1. Orforglipron for Maintenance of Body Weight Reduction: ATTAIN-MAINTAIN. Nature Medicine. May 2026. DOI: 10.1038/s41591-026-04386-7. Nature Medicine
2. Lilly’s Foundayo and Lower-Dose Zepbound Helped People Maintain Weight Loss After Switching From Higher Doses of Injectable Incretin Therapy in Two Late-Phase Trials. Lilly Press Release. May 13, 2026. PRNewsWire
3. Injectable-to-Oral Obesity Drug Switch Maintains Weight Loss. EurekAlert. May 13, 2026. EurekAlert
4. Orforglipron Shows Strong Weight Maintenance in Phase 3 ATTAIN-MAINTAIN Trial. Pharmacy Times. May 13, 2026. Pharmacy Times
5. Oral GLP-1 Medication Helps Patients Maintain Weight Loss. Weill Cornell Medicine. May 2026. Weill Cornell Medicine