Written by Mandy French — Fact checked by Jill Seladi-Schulman, Ph.D.
Eli Lilly’s new experimental weight loss drug retatrutide showed the greatest weight loss in a medication trial to date.
The phase 3 results of the TRIUMPH-1 trial showed the drug yielded up to 28% weight loss, with some participants losing up to 85 pounds.
Retatrutide is a triple hormone agonist administered by once-weekly injection.
The drug activates glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon, whereas weight loss drugs like Ozempic and Wegovy activate only the GLP-1 receptor.
Lilly noted in a press release that at 80 weeks, all the doses of retatrutide “met the primary and key secondary endpoints for obesity, delivering clinically meaningful weight loss.”
“TRIUMPH-1 highlights the importance of options and the potential for retatrutide to help people across various stages of their obesity journey,” Kenneth Custer, PhD, executive vice president and president, Lilly Cardiometabolic Health, said in a press release.
“Together with Zepbound and Foundayo, retatrutide could build on Lilly’s commitment to match treatments to the needs and preferences of patients.”
Experts agreed that retatrutide shows promise as a highly effective first-in-class treatment for obesity.
“These results indicate that retatrutide is a promising new drug that appears more effective than currently available medications,” said Mir Ali, MD, bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA. Ali wasn’t involved in the trial.
Lilly’s new drug yields up to 85 pounds weight loss
In the TRIUMPH-1 trial, participants were given either 4 mg, 9 mg, or 12 mg of retatrutide.
At the end of 80 weeks, participants on each dose lost the following amount of weight on average:
- 4 mg: 19% or around 47 lbs
- 9 mg: 25.9% or about 64 lbs
- 12 mg: 28.3% or around 70 lbs
These numbers compare to participants who received a placebo and lost an average of 2.2%, or about 5.5 lbs.
At 104 weeks, participants with a baseline body mass index (BMI) of at least 35 achieved an average weight loss of 30.3% (85 lbs).
“It was impressive to see that every dose of retatrutide resulted in clinically meaningful weight reduction for nearly all participants, and people with severe obesity on the highest dose lost on average 30% of their body weight over two years,” lead investigator Ania Jastreboff, MD, professor of medicine and pediatrics at the Yale School of Medicine and director of the Yale Obesity Research Center, said in a press release.
“Importantly, treatment with retatrutide not only resulted in robust weight reduction, but also in clear improvements in assessed cardiometabolic health measures. For patients I see in [the] clinic, retatrutide may potentially be a highly impactful future tool to treat their obesity and transform their health trajectory.”
Participants also saw significant improvements to certain cardiovascular risk factors, including:
“While this medication has the potential to be the most effective option, long-term studies are not yet available,” Ali told Healthline.
“Side-by-side comparisons with currently available medications have yet to be determined. Like all weight loss medications, this drug will require long-term use as obesity is a chronic medical condition. At this point, the biggest hurdles for widespread implementation will be availability and insurance coverage,” he said.
Side effects of Lilly’s new weight loss drug
The most common side effects of retatrutide among participants were similar to those of other GLP-1 medications:
- nausea
- diarrhea
- constipation
- vomiting
- upper respiratory tract infection
A small number of participants also experienced dysesthesia and urinary tract infections (UTIs).
Incidents of dysesthesia and UTIs were generally mild to moderate. The majority of them resolved during treatment, and most participants continued taking retatrutide.
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