The weekly injectable therapy produced levels of weight reduction rarely seen outside bariatric surgery, reinforcing expectations that the drug could become one of the most powerful obesity treatments developed so far.
According to trial data released Thursday, patients taking the highest dose of retatrutide lost an average of 28.3% of their body weight over 80 weeks — equivalent to roughly 70 pounds. By comparison, participants receiving placebo treatment lost just 2.2%.
Even more notably, nearly 45% of the approximately 2,500 participants achieved at least 30% weight loss during the Phase 3 study, a benchmark experts have historically associated with surgical intervention rather than medication.
Dan Skovronsky, Lilly’s chief scientific and product officer, described the outcome as unprecedented for obesity drugs.
“We haven’t seen that level of weight loss before with these kinds of medicines,” Skovronsky said in an interview with CNBC.
He added that seeing patients reach 30% weight loss was “an incredible number to see,” emphasizing that such results had previously been linked mainly to bariatric surgery.
The findings place Lilly in a stronger competitive position against Danish rival Novo Nordisk, whose blockbuster obesity drug Wegovy currently dominates parts of the global market. Analysts had anticipated retatrutide would outperform Lilly’s own hit medication, Zepbound, which typically delivers around 20% to 22% weight loss.
A Different Kind of Weight-Loss Drug
Retatrutide has drawn intense attention because of how it works. Unlike current obesity medications that target one or two gut hormones, the experimental drug acts on three: GLP-1, GIP, and glucagon.
The so-called “triple G” approach appears to amplify appetite suppression while also increasing energy expenditure, potentially explaining the dramatic reductions in body weight observed in trials.
By comparison, Lilly’s Zepbound contains tirzepatide, which targets GLP-1 and GIP, while Novo Nordisk’s Wegovy relies solely on GLP-1.
Researchers say the broader hormone-targeting strategy may give retatrutide a significant edge in effectiveness, although questions remain about long-term tolerability and side effects.
Lower Dose Also Shows Promise
Beyond the headline-grabbing results from the highest dose, Lilly also tested a lower 4-milligram version of retatrutide — one that had not been used in previous studies.
Patients on that lower dose still lost an average of 19% of their body weight, or about 47 pounds, over the same 80-week period. Importantly, the lower dose appeared easier for patients to tolerate.
Only about 4% of participants on the 4-milligram dose discontinued treatment because of side effects, compared with nearly 5% in the placebo group. Meanwhile, discontinuation rates climbed to 11.3% among patients receiving the highest dose.
Skovronsky said the lower-dose data may prove just as important as the high-dose findings.
“For some patients, 30% weight loss may be more than what they’re seeking,” he explained. “For other patients, that may be what they need to get healthy.”
He added that not every patient would necessarily remain on the highest dose long term.
Safety Concerns Remain Under Watch
As with other GLP-1-related medications, gastrointestinal side effects were the most common issues reported during the trial.
Among patients receiving the highest dose:
- Around 42% experienced nausea
- Roughly 32% reported diarrhea
- About 26% dealt with constipation
More than 13% also developed upper respiratory tract infections, while over 12% experienced dysesthesia — an unpleasant nerve sensation previously observed in earlier studies of the drug.
Analysts had been especially focused on whether retatrutide might trigger heart-related complications because of its glucagon component, which affects energy expenditure and metabolism. However, Lilly said the study revealed no significant cardiac or liver safety concerns.
The company did observe slightly elevated rates of urinary tract infections among patients on the drug. More than 8% of participants taking the highest dose experienced UTIs, though Lilly noted that most cases were mild and resolved while treatment continued.
Skovronsky suggested the infections may be linked to the rapid pace of weight loss itself.
“It may be the result of the velocity of weight loss,” he said, noting similar patterns have also been seen following bariatric surgery.
Lilly Strengthens Its Lead in the Obesity Drug Race
The latest trial marks the third successful late-stage study involving retatrutide. Earlier this year, the drug also showed positive outcomes in diabetes patients, following another successful study in obesity patients suffering from knee arthritis pain.
The momentum further strengthens Lilly’s position in what analysts believe could become a $100 billion global obesity and diabetes drug market by the 2030s.
According to company data, Lilly controlled approximately 60.1% of the U.S. obesity and diabetes drug market during the first quarter, compared with Novo Nordisk’s 39.4%.
Industry analysts at TD Cowen have projected that retatrutide alone could generate roughly $3.8 billion in annual sales by 2030.
Meanwhile, Novo Nordisk is racing to respond. In March 2025, the company agreed to pay up to $2 billion for rights to an experimental triple-action obesity drug from Chinese pharmaceutical firm United Laboratories International.
Still, Novo’s candidate remains in much earlier stages of development, meaning Lilly may enjoy a substantial head start if retatrutide secures regulatory approval in the coming years.