But these are powerful medications that affect very highly conserved areas of tetrapod biology. We discovered GLPs in the mouths of gila monsters, after all. So you then can infer that that the mechanism is at least 300 million years old (our last common ancestor with lizards).
Actually, I tried looking this up, and glucagon is likely 5-600 million years old, back to all chordates, the Cambrian explosion essentially, though likely even before that. So, incredibly conserved. Like, if you are a multicellular animal, odds are you have some glucagon-like thing for digestion regulation.[0]
We're strongly messing with a system that is just tremendously old. Biology and evolution are ruthless about this stuff, it edits it out as fast as it possibly can. That it's been so closely held is a very big sign for us that we need to tread extremely carefully.
Like, clearly, other countries do not have these issues with weight. Yes, they are developing them, I know. But even the US didn't have these issues near as bad just two generations ago, a blink in biological terms. You and I both know that the solution is not a pill, but the root cause of the obesity epidemic itself. These injections and pill are just band-aids for a much deeper and more pernicious problem.
But then again, you and I both know that we're not going to get at the root cause anytime soon either.
[0] This is biology so you'll find exceptions everywhere though