Eli Lilly's New Weight Loss Drug Achieves Phase III Success, with Weight Loss Approaching Surgical Outcomes

According to Bloomberg's report on Thursday, Eli Lilly's new generation weight loss drug, retatrutide, has achieved breakthrough results in a key Phase 3 clinical trial. The trial included approximately 2,500 patients who were either obese or overweight, testing three dose groups ranging from 4mg to 12mg. All doses met the primary endpoint of clinical meaningful weight loss.

The highest dose group of patients achieved an average weight loss of 28.3%, equivalent to about 31.9 kilograms, within 80 weeks, with about 45% of participants experiencing a weight reduction of 30% or more. In patients with a BMI of 35 or above, participating in an extended study, the highest dose group achieved an average weight loss of 30.3% within 104 weeks. Approximately 65% of the patients saw their BMI drop below 30, moving out of the obese category.

The president of Eli Lilly's Cardiovascular and Metabolic Health division, Kenneth Custer, stated, "We are in the historical range associated with weight loss surgery, and you are achieving it through a medication." In contrast, Eli Lilly's existing star weight loss drug, Zepbound, has a weight loss range of about 20% to 22%, which has been significantly surpassed by the highest dose group of retatrutide.

The low-dose group also performed impressively. Patients in the 4mg dose group achieved an average weight loss of 19%, comparable to the high dose effect of Zepbound, but with superior tolerance — the proportion of patients discontinuing the medication due to side effects was about 4%, even lower than the nearly 5% of the placebo group. Eli Lilly's Chief Scientific and Product Officer, Dan Skovronsky, called this result "remarkable".

In terms of safety, the most common side effects were gastrointestinal reactions. About 42% of patients in the highest dose group experienced nausea, and about 32% experienced diarrhea. There had been market concerns that the drug might cause arrhythmia and other heart issues due to its targeting of glucagon. Eli Lilly stated that no heart or liver issues were observed during the trial.

The core differentiating advantage of retatrutide lies in its triple hormone mechanism — targeting GLP-1, GIP, and glucagon simultaneously, whereas Zepbound targets two, and Novo Nordisk's Wegovy targets only one. This mechanism is considered key to achieving its stronger weight loss effects.

Analysts from RBC Capital Markets called the results an "unambiguous win" for Eli Lilly. TD Cowen previously estimated that retatrutide could achieve sales of $3.8 billion by 2030. With Zepbound and oral medication Foundayo, Eli Lilly positions it as the next core pillar of its obesity product line. The success of the Phase 3 trial brings it a step closer to formally submitting regulatory approval.