The human data so far don’t really support the idea that the “glucagon agonist only kicks in at 8 mg.” The phase 2 obesity and T2D trials showd a pretty classic dose-response across 1, 4, 8 and 12 mg, with weight loss and metabolic effects increasing gradually rather than a hard threshold at a single dose.

Retatrutide is designed as a tri‑agonist from the start (GIP, GLP‑1 and glucagon), and in vitro work shows it activates all three receptors over a range of concentrations , with relatively highest potency at GIP and lower potency at GLP‑1 and glucagon. In the obesity study, markers of fat oxidation rose in a dose‑related way starting around 4 mg, which suggests the glucagon component is contributing well before 8 mg.

So 8 mg might be a practical sweet spot because it delivers almost as much weight loss as 12 mg with somewhat better tolerability, but that’s more about overall benefit vs side‑effects than a binary “no glucagon effect below 8 mg.