Eli Lilly announced that its next-generation anti-obesity drug has successfully completed a pivotal late-stage clinical trial for obesity, demonstrating significant weight loss across all dosage groups.
The weekly injectable drug, known as retatrutide, has moved a step closer to submitting its application for market approval. Its mechanism of action differs from existing injectable and oral anti-obesity medications.
Participants in the highest dosage group achieved an average weight reduction of 28.3% over 80 weeks, equivalent to 70.3 pounds.
Eli Lilly disclosed on Thursday that its next-generation anti-obesity drug successfully passed a critical Phase III clinical trial for obesity, with various dosages showing substantial weight loss results.
The trial outcomes advance the weekly formulation, retatrutide, toward the regulatory approval process. The drug's mechanism differs from Eli Lilly and Novo Nordisk's current range of injectable and oral anti-obesity drugs and offers superior efficacy.
Analyzing data only from participants who adhered to the treatment throughout the trial, the highest dosage group achieved an average weight loss of 28.3% over 80 weeks, equivalent to 70.3 pounds, while the placebo group saw a mere 2.2% reduction.
This Phase III trial involved 2,500 participants, with approximately 45% achieving a weight loss of 30% or more.
In an extension study focusing on high-risk obese individuals with a body mass index of 35 or higher, the highest dosage group showed an average weight reduction of 30.3% after 104 weeks. This BMI range is associated with a higher risk of cardiovascular diseases and diabetes.
The drug presents some gastrointestinal side effects, with nausea and diarrhea being more common at higher doses. The overall adverse reaction profile aligns with a previous Phase III trial involving obese patients with knee osteoarthritis. Industry analysis suggests that these side effects indirectly indicate the drug's rapid onset and potent efficacy.
The lower-dose version tested in this trial resulted in a lower discontinuation rate due to adverse reactions.
Dan Skovronsky, Eli Lilly's Chief Scientific and Medical Officer, stated that a 30% weight reduction is exceptionally impressive, a level previously only attainable through bariatric surgery.
"Conventional weight-loss medications have never achieved such a degree of weight reduction," he added.
After 80 weeks of treatment, about 65% of participants in the highest dosage group reduced their BMI to below 30, moving out of the obesity classification.
Market expectations had previously anticipated that this drug would surpass the weight loss efficacy of Eli Lilly's blockbuster drug, Zepbound, which achieves approximately 20% to 22% weight reduction.
This marks the third successful late-stage clinical trial for retatrutide. Earlier this year, its diabetes clinical trial concluded successfully, and in December last year, it completed a smaller trial for obesity combined with knee osteoarthritis. Following injectable Zepbound and the new oral drug, orforglipron, Eli Lilly views retatrutide as a core new product in its obesity drug pipeline.
Cowen Securities forecasts that the drug could achieve sales of $3.8 billion by 2030.
The market for weight loss and diabetes medications continues to expand, with industry estimates projecting the overall market value to exceed $100 billion by the 2030s. Retatrutide is a key product for Eli Lilly to maintain its dominant market share and compete against Novo Nordisk.
New Low-Dose Regimen
This trial tested a 4 mg low-dose formulation for the first time, with participants achieving an average weight loss of 19% over 80 weeks, equivalent to 47.2 pounds.
This low-dose weight loss effect matches the high-dose performance of Zepbound, with tolerability exceeding expectations. Gastrointestinal adverse reactions are common with GLP-1 class drugs, but this low-dose formulation demonstrated excellent tolerability.
The discontinuation rate due to side effects in the 4 mg dosage group was about 4%, lower than the nearly 5% discontinuation rate in the placebo group. The highest dosage group had a discontinuation rate of 11.3%.
Skovronsky noted that both high and low doses delivered outstanding data, marking a milestone. Weight loss varies among individuals, and some patients may not require maximum reduction; selecting doses based on need can adequately meet health requirements.
Medication Safety
Overall safety performance is consistent with similar GLP-1 drugs, with adverse reactions primarily being gastrointestinal discomfort.
In the highest dosage group, 42% of participants experienced nausea, with diarrhea and constipation occurring at rates of 32% and 26.1%, respectively. Over 13% developed upper respiratory infections, and more than 12% reported abnormal neurological sensations.
The market had previously expressed concerns about potential cardiac issues, such as arrhythmias. The drug acts on three gut hormones, including glucagon, which increases energy expenditure.
Eli Lilly reported that the trial found no adverse cardiac or liver-related conditions. The incidence of urinary tract infections was slightly higher in the treatment group compared to the placebo group, with most cases being mild and resolving during treatment. The infection rate in the high-dose group exceeded 8%. The exact cause remains unclear but is speculated to be linked to rapid weight loss, a phenomenon also observed with bariatric surgery.
Mechanism of Action
Retatrutide is a triple-target drug, simultaneously acting on GLP-1, GIP, and glucagon hormones. Compared to traditional drugs targeting only one or two pathways, it offers stronger appetite control and satiety regulation.
Zepbound's active ingredient, tirzepatide, targets GLP-1 and GIP, while Novo Nordisk's Wegovy, with semaglutide, acts solely on the GLP-1 target.
Financial reports indicate that in the first quarter of this year, Eli Lilly held a 60.1% share of the U.S. weight loss and diabetes drug market, with Novo Nordisk accounting for 39.4%.
As retatrutide nears market entry, Novo Nordisk is accelerating its competitive efforts. In March 2025, Novo Nordisk invested up to $2 billion to secure the rights to an early-stage trial drug from China's United Laboratories.
This new drug also employs a triple-action mechanism to regulate blood sugar and reduce weight, posing potential competition to retatrutide. However, it lags significantly in development progress and is several years away from market availability.
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