Retatrutide.

Retatrutide is a 39-amino-acid peptide built on a backbone derived from GIP (glucose-dependent insulinotropic polypeptide), modified to activate three G-protein-coupled receptors at once: the GLP-1 receptor (GLP-1R), the GIP receptor (GIPR) and the glucagon receptor (GCGR). A C20 fatty-acid chain conjugated to the peptide extends its half-life to roughly six days in pharmacokinetic models, which is what made the once-weekly schedules used in clinical trials possible.

GLP-1R activation reproduces the incretin pathway: glucose-dependent stimulation of insulin secretion, slowed gastric emptying and a satiety signal at the hypothalamic level. That is the arm retatrutide shares with semaglutide. GIPR activation, shared with tirzepatide, potentiates the insulin response and modulates adipose-tissue metabolism. The third arm — GCGR activation — is what sets retatrutide apart: in preclinical models it raises energy expenditure and hepatic lipid oxidation, a combination that accounts for the magnitude of the weight reductions seen first in animal studies and then in phase 2 trials.

For laboratories, this triple profile makes it an unusually useful tool for studying metabolic signalling: comparing single, dual and triple agonism within one experimental system, and work on energy balance, hepatic lipid metabolism or incretin biology. The phase 3 work in the TRIUMPH programme (obesity, type 2 diabetes and associated comorbidities) keeps adding to the literature and opens new questions for basic research.