The glucagon signal

Retatrutide switches on the glucagon receptor, the arm that tirzepatide does not have. In the liver, glucagon turns on fat burning and ketone production and pulls stored fat out of liver cells. Across the body it raises energy use, so you burn more fuel at rest. The GLP-1 and GIP arms hold blood sugar steady while the glucagon arm burns fat, which is why the three together work better than any pair.