Retatrutide, the first peptide to simultaneously target GLP-1, GIP, and glucagon receptors, produced up to 18% weight loss in 24 weeks — but head-to-head comparisons with semaglutide and tirzepatide are notably absent.
Up to ~18% weight loss in 24 weeksThe highest dose of retatrutide (12 mg) produced approximately 18% body weight reduction in just 24 weeks — suggesting even greater potential with longer treatment duration
What the researchers found
In a phase 2 clinical trial, retatrutide — the first triple-agonist peptide targeting GLP-1, GIP, and glucagon receptors simultaneously — produced dose-dependent weight loss ranging from 7.2% to approximately 18% over just 24 weeks. These results are remarkable given the short study duration, suggesting even greater weight loss with longer treatment. The most common side effects were gastrointestinal (nausea, diarrhea, vomiting), consistent with GLP-1 receptor agonism.
The author notes a concern: retatrutide increased heart rate by up to 6.7 beats per minute, which may partially offset the cardiovascular benefits of weight loss. Critically, no head-to-head comparator trials against semaglutide or tirzepatide are ongoing, which the author views as a significant gap in the drug's development.
Why it matters
Retatrutide represents the next frontier in peptide-based obesity treatment — moving from single-agonist (semaglutide/GLP-1) and dual-agonist (tirzepatide/GLP-1+GIP) to triple-agonist therapy. Adding glucagon receptor activation to the mix could enhance weight loss through increased energy expenditure and fat burning, potentially outperforming existing drugs. However, without head-to-head comparisons, its place in the treatment hierarchy relative to semaglutide and tirzepatide remains unclear.
The numbers in context
Weight loss: -7.2% to -~18% over 24 weeks · Doses: 1 mg to 12 mg · Heart rate increase: up to +6.7 bpm · 3 receptor targets: GLP-1, GIP, glucagon · Most common AEs: nausea, diarrhea, vomiting
How the study worked
This is an expert opinion commentary reviewing results from a phase 2 dose-ranging clinical trial of retatrutide (LY3437943) in obesity. The primary endpoint was percentage weight change from baseline to 24 weeks across dose groups.
Who was studied
Adults with obesity (phase 2 clinical trial population)
What this study cannot tell us
This commentary reviews phase 2 data only — the trial had a relatively short 24-week duration. No head-to-head comparator studies with semaglutide or tirzepatide exist, making it impossible to directly compare efficacy. The heart rate increase raises cardiovascular safety questions requiring long-term monitoring. Phase 3 data and long-term safety outcomes are needed.
How to read the evidence
This is an expert commentary on phase 2 clinical trial data. While phase 2 results are encouraging, they involve fewer patients and shorter duration than definitive phase 3 trials. The lack of comparator arms limits interpretation. Evidence is moderate — promising but not yet definitive.
When this study was published
Published in 2023, this commentary covers the earliest phase 2 data for retatrutide. Phase 3 trials may now be underway, and more recent data may provide longer-term efficacy and safety information.
The bigger picture
The obesity drug landscape is evolving rapidly from single-target GLP-1 agonists (semaglutide) to dual agonists (tirzepatide targets GLP-1 + GIP) to now triple agonists (retatrutide adds glucagon). Each generation has produced progressively greater weight loss. Glucagon receptor activation is the key new addition — it increases energy expenditure and promotes fat breakdown, complementing the appetite-suppressing effects of GLP-1 and GIP. However, glucagon also raises blood glucose, so the balance of the three receptor activities is critical. Retatrutide's development will test whether triple agonism truly outperforms dual agonism.
Questions still open
- Will phase 3 trials confirm the magnitude of weight loss seen at 24 weeks, and will it continue with longer treatment?
- Is the heart rate increase of up to 6.7 bpm clinically significant for long-term cardiovascular outcomes?
- When will head-to-head comparator trials with semaglutide and tirzepatide be conducted to establish retatrutide's relative efficacy?
Common questions
What makes retatrutide different from semaglutide and tirzepatide?
Why is the heart rate increase a concern?
Read the original research
Retatrutide showing promise in obesity (and type 2 diabetes).
Expert opinion on investigational drugs, 32(11), 997-1001
Citation
Doggrell, Sheila A. (2023). Retatrutide showing promise in obesity (and type 2 diabetes).. Expert opinion on investigational drugs, 32(11), 997-1001. https://doi.org/10.1080/13543784.2023.2283020