An experimental obesity drug from Eli Lilly has produced striking weight loss in a large clinical trial, with results rivaling gastric bypass surgery in some of the heaviest patients, according to a report in The New York Times.

Eli Lilly's injectable drug retatrutide enabled participants in a randomized study of 2,339 adults with obesity or overweight to lose far more weight than is typically seen with today's leading obesity medications, the company said in an announcement cited by The New York Times. At the highest dose tested, patients lost an average of 70 pounds (31.7kg), or 28 per cent of their body weight, after 80 weeks of treatment.

In a subgroup of participants with a body mass index (BMI) over 35 -- classified as moderate to severe obesity -- the results over a longer period were even more dramatic. After roughly two years on the top dose, these patients lost about 85 pounds (38.5 kg) on average, or 30.3 per cent of body weight, a degree of weight reduction comparable to the 30–35 per cent typically achieved two years after gastric bypass surgery.

Gastric bypass is currently the only consistently effective intervention for most people with severe obesity, but it remains invasive and relatively unpopular.

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The trial results, which have not yet undergone peer review or been published in a medical journal, were released by the company and first detailed in The New York Times.

Stronger than existing obesity drugs, but...

The weight loss seen with retatrutide exceeds what is normally possible with today's blockbuster obesity injections, Eli Lilly's Zepbound and Novo Nordisk's Wegovy, The New York Times noted. Those drugs, which act on the GLP‑1 hormone, generally help patients lose about 20 per cent of their body weight over a similar timeframe, while oral versions typically produce 12–14 per cent weight loss.

For the estimated 24 million Americans with "severe obesity" (BMI of at least 40), that level of reduction is often not enough to reach a healthy weight. Many such patients need to shed 80–100 pounds, according to Dr Carolyn Apovian, an obesity specialist at Harvard Medical School quoted by the newspaper. Bariatric surgery can deliver that degree of loss, but demand for surgery has fallen as injectable drugs have become more popular.

Retatrutide's greater potency appears to come at a cost. Like other drugs in this class, it frequently causes gastrointestinal side effects such as nausea, vomiting, diarrhoea and constipation, but The New York Times reports that these problems were more common and intense at higher doses.

About 11 per cent of participants on the highest dose dropped out of the trial because of side effects, a higher discontinuation rate than has been seen with current obesity injections.

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At lower doses, however, tolerability was better. In an unexpected twist described in the Times report, more people on placebo stopped taking their injections because of perceived side effects than those on the lowest dose of retatrutide.

At that dose, patients still lost about 19 per cent of their body weight -- roughly the amount achieved with the maximum dose of Zepbound -- suggesting the drug could be both powerful and reasonably well tolerated at modest strengths.

How retatrutide works

Retatrutide is injected once a week, with the dose gradually increased over time to limit stomach‑related side effects, following a titration strategy similar to Wegovy and Zepbound. But biologically, it goes further than those medicines.

As described by The New York Times, retatrutide is a "souped‑up" version of the GLP‑1 drugs: it acts on three hormones involved in appetite, energy balance and metabolism.

* GLP‑1, the hormone targeted by Wegovy and Zepbound

* GIP, an additional hormone also targeted by Zepbound

* Glucagon, a third hormone that neither Wegovy nor Zepbound affects

This "triple agonist" design appears to amplify weight loss beyond what has been seen when only one or two of these hormones are targeted, although researchers interviewed by the Times said it is still unclear exactly why the combination is so effective.

Dr Ania Jastreboff, an obesity specialist at Yale and principal investigator for the study, told The New York Times that retatrutide's results were "very impressive, no doubt". However, she stressed that obesity is a chronic disease, and that the key question is not only how many kilograms patients lose in the short term but how the drug affects their health over a lifetime.

Demand, knockoffs and regulatory battles

Retatrutide has not yet been submitted for regulatory approval, but the scale of weight loss reported has already sparked intense interest and some unintended consequences.

As word of early trial results spread, some Americans began ordering purported versions of the drug from unregulated online suppliers in China, a trend that has alarmed doctors and researchers quoted by The New York Times, who worry that patients are taking copycat compounds without medical supervision and could be harmed.

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If eventually approved, retatrutide would enter an increasingly crowded obesity‑drug market, yet some clinicians told the Times they expect it could be particularly valuable for the heaviest patients who need to lose the most weight but are reluctant to undergo bariatric surgery.

For Eli Lilly, the drug also carries major commercial stakes. The company's revenues have already surged thanks to Zepbound for obesity and Mounjaro for diabetes, helping it become the first health‑care firm to reach a $1 trillion market value last year, The New York Times reported.

Lilly is simultaneously embroiled in a legal fight with the US Food and Drug Administration over how retatrutide should be classified. According to the Times, the company sued the FDA in 2024, arguing that the agency wrongly treated retatrutide as a traditional small‑molecule drug rather than a biologic, in a dispute centred on its precise amino‑acid structure.

A reclassification as a biologic could grant Lilly longer market exclusivity, potentially worth billions of dollars, by delaying when competitors can sell similar versions and allowing the firm to charge higher prices for more years.

Big promise, big unknowns

Experts quoted in The New York Times cautioned that important questions remain: whether the impressive weight loss will plateau or wane over time, how safe the drug will prove in real‑world use outside controlled trials, and whether patients will be willing or able to stay on long‑term therapy despite side effects and cost.

If retatrutide's benefits hold up, and its real‑world performance matches the clinical trial, the drug could expand what doctors and patients expect from weight‑loss medicines, potentially offering a non‑surgical path to surgery‑like results for many people living with severe obesity, the New York Times analysis suggested.