Retatrutide vs Tirzepatide
Category
Metabolic & GLP-1
Metabolic & GLP-1
Class
Triple GIP/GLP-1/glucagon receptor agonist (investigational peptide)
Dual GIP/GLP-1 receptor agonist (synthetic peptide)
Regulatory status
Not FDA-approved; investigational, in clinical trials
FDA-approved (Mounjaro for type 2 diabetes; Zepbound for weight management)
Mechanism
Retatrutide is a single peptide designed to activate three receptors involved in metabolism: GIP, GLP-1, and the glucagon receptor.
Tirzepatide is a single peptide that activates both the GIP and GLP-1 receptors, two incretin pathways involved in glucose control and appetite.
Evidence summary
Retatrutide has promising but still early human evidence. Phase 2 trials reported large average weight reductions over several months, and phase 3 studies are underway. Because the long-term efficacy and safety profile is not yet established, the overall evidence is best described as moderate.
Tirzepatide has strong human evidence from the SURPASS (diabetes) and SURMOUNT (obesity) trial programs, which showed large reductions in HbA1c and body weight, in several comparisons exceeding those seen with single GLP-1 agonists. It is a well-studied, approved medicine.
Reported safety
Reported side effects in trials have been mainly gastrointestinal (nausea, diarrhea, vomiting), consistent with the drug class. As an investigational agent, its full safety profile, including long-term and rare effects, is not yet established.
The most common side effects are gastrointestinal (nausea, diarrhea, vomiting, constipation), typically dose-related. Like other incretin drugs it carries a boxed warning about thyroid C-cell tumors based on rodent data and requires medical supervision.