Retatrutide Produces Greatest Weight Loss

A systematic review of 26 randomized controlled trials (RCTs) finds that among glucagon-like peptide 1 (GLP-1) receptor agonists and co-agonists on the market or still being investigated, the experimental drug retatrutide (Eli Lilly and Company) produces the greatest weight loss.

The review, conducted by researchers at McGill University, Montreal, Quebec, Canada, examined three commercially available medications in the class and nine that have not yet received regulatory approval.

In healthy adults with overweight or obesity who did not have diabetes, the highest mean reductions in relative and absolute body weight were achieved with once-weekly triple glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 and glucagon receptor agonist retatrutide, followed by the dual GIP/GLP-1 agonist tirzepatide (Eli Lilly and Company) and lastly by the GLP-1 agonist semaglutide (Novo Nordisk), according to the authors.

The use of all the GLP-1s or co-agonist medications “led to decreased body mass index (BMI), waist circumference, SBP (systolic blood pressure), and DBP (diastolic blood pressure),” wrote the authors in the Annals of Internal Medicine. All the medications had a similar safety profile.

The researchers did not find any head-to-head studies, so instead examined the results from 26 RCTs that enrolled more than 15,000 patients. Only trials with a treatment duration of at least 16 weeks were included, to ensure that patients had at least a month of a fixed dose.

Not surprisingly, the review found that, except for semaglutide, trials with “dual and triple agonists generally reported numerically greater mean weight losses than single GLP-1 agonists.”

They caution, however, against drawing conclusions about comparative efficacy, as the populations, control groups, and contexts of the various studies might not be directly comparable. All the trial enrollees also received lifestyle modification along with drug therapy or placebo, but the interventions and protocols varied across the studies.

The authors found that individuals on retatrutide (12 mg once-weekly injection) lost 22% of body weight from baseline after 48 weeks. Tirzepatide (15 mg once-weekly injection) recipients lost almost 18% of body weight after 72 weeks, while those on semaglutide (2.4 mg once-weekly injection) lost about 14% after 68 weeks. Both tirzepatide and semaglutide are commercially available.

Patients taking liraglutide (3 mg once-daily injection), also on the market, lost up to 6% of body weight after 26 weeks.

The authors also examined studies of investigational agents and reported that the greatest loss, aside from retatrutide, was with the dual glucagon/GLP-1 agonists survodutide (Boehringer Ingelheim; 6%-15%) and the mazdutide (Innovent Biologics; 7%-11%).

Orforglipron (Eli Lilly and Company), a once-daily pill, produced weight loss of 9%-15%, depending on the dose.

The study found that four investigational drugs did not produce as much weight loss: Beinaglutide (0.2 mg injection three times daily, 6%), efpeglenatide (4-8 mg injection once weekly, about 7%), exenatide (10 mcg injection twice daily, 5 kg change in weight), and noiiglutide (once-daily injection, 9%).

The most common adverse events for all GLP-1s were gastrointestinal (GI), such as nausea, diarrhea, constipation, and vomiting. Across all agents, 60%-80% of patients taking the medications experienced a GI adverse event, although most were transient, according to the authors. A total of 6%-26% of patients discontinued treatment as a result of a side effect.

The authors said that no serious GI disorders, such as bowel obstruction or gastroparesis, were reported in any of the 26 trials.

The review also shows that it is likely that GLP-1s would have to be used chronically to have the greatest effect, said the authors. They noted that they found that trials “with longer treatment durations demonstrate similar weight loss results to those with shorter follow-up, reinforcing the idea that continuous treatment may be required.”

Michael Tsoukas, MD, reported receiving payments or honoraria from Boehringer Ingelheim, Eli Lilly and Company, Janssen Pharmaceuticals, and Novo Nordisk. The study was carried out independently without any grant or other funding.

Alicia Ault is a Saint Petersburg, Florida-based freelance journalist whose work has appeared in many health and science publications, including Smithsonian.com. You can find her on X @aliciaault and on Bluesky @aliciaault.bsky.social.